,,the ,,petrol ,,engine ,,books ,,for ,,motor ,,engineers4 ,electrical ,ignition for ,internal ,combustion ,engines4 ,by ,m4 ,a4 ,codd4 #aji illus41 #afc pp41 cr4 #hvo4 #cs4 net4 ,introduction--,principle of ,electric ,flow--,batteries--,switches--,coils--,a uto-,tremblers--,lodge ,ignition--,distributors--,magneto ,ignition--,high ,tension ,magnetos--,faults and ,remedies--,magneto ,repairs--,induction ,coil ,design--,index4 ,dynamo ,lighting for ,motor ,cars4 ,by ,m4 ,a4 ,codd1 ,author of 8,electrical ,ignition for ,internal ,combustion ,engines40 #abh illus41 vi #if pp4 #hvo4 #bs4 #f;d4 net4 ,introduction and ,general ,principles--,fitting the ,system--,wiring the ,car--,permanent ,magnet ,system--,permanent and ,electro-,magnet ,system--,electro-,magnetically ,governed ,system--,electro-,magnetically ,controlled ,system--,mechanically ,controlled ,system--,hot ,wire ,controlled ,system--,some useful ,accessories--,upkeep1 ,maintenance1 and ,location of ,faults--,index4 ,english-,french and ,french-,english ,dictionary of the ,motor ,car1 ,cycle and ,boat4 ,by ,frederick ,lucas4 #aga pp41 cr4 #hvo4 #bs4 net4 ,motor ,cycles1 ,side ,cars and ,cycle ,cars1 ,construction1 ,management and ,repair4 ,by ,v4 ,w4 ,page1 ,m4,e4 ,a comprehensive non-technical treatise1 defining all forms of the lighter self-propelled vehicles1 principles of operation1 construction1 and practical application of component parts4 #hvo1 #cdd illus41 #eej pp4 7,new ,york47 #fs4 #f;d4 net4 ,the ,modern ,gasolene ,automobile1 its ,design1 ,construction1 ,maintenance and ,repair4 ,by ,victor ,w4 ,page1 ,m4,e41 late ,technical ,editor of the 8,automobile ,journal40 #ejj illus41 #fic pp41 #hvo4 7,new ,york47 #abs4 net4 ,drawings for ,medium ,sized ,repetition ,work1 with ,examples of ,drawings for ,motor-,car ,parts4 ,by ,r4 ,d4 ,spinney1 ,a4,m4,i4,mech4,e4 #dg illus41 #acj pp41 #hvo4 #cs4 #f;d4 net4 ,motor ,body ,building in all its branches4 ,by ,c4 ,w4 ,terry1 ,organizer and ,inspector of the ,city and ,guilds of ,london ,institute4 ,with additional matter by ,arthur ,hall1 ,graduate member of 8,the ,institute of ,british ,carriage ,manufacturers10 #ast class certificate in honours of the ,city and ,guilds of ,london ,institute1 and other awards2 ,instructor in ,motor ,body ,building1 ,municipal ,technical ,college1 ,brighton1 etc41 etc4 ,medium #hvo1 #bef pp41 #ae illus41 #e plates4 #ajs4 #f;d4 net4 ,e4 ,f4 ,n4 ,,spon1 ,,ltd41 #eg ,,haymarket1 ,,london1 ,s4,w4 ,the ,petrol ,engine ,a ,text-book dealing with the ,principles of ,design and ,construction1 with a ,special ,chapter on the ,two-stroke ,engine ,by ,,francis ,,john ,,kean ,b4,,sc4 7,,lond472 ,m4,i4,m4,e4 ,first-,class ,honourman in ,engineering2 ,head of the ,motor ,car ,engineering ,department of the ,polytechnic ,school of ,engineering1 ,regent ,street1 ,london1 ,w42 ,formerly ,lecturer on ,experimental ,engineering at ,mc,gill ,university1 ,montreal1 ,canada #ga ,,illustrations ,colophon ,london ,e4 ,f4 ,n4 ,,spon1 ,,limited1 #eg ,,haymarket ,new ,york ,,spon ,,chamberlain1 #abc ,,liberty ,,street #aiae ,,contents ,,page ,,list ,,of ,,illustrations ix ,,preface xiii ,,chapter ,i ,,general ,,principles-- ,explosive ,mixtures #a ,the ,meaning of ,suction #b ,the ,meaning of ,compression #c ,the ,meaning of a ,stroke #c ,the ,otto ,cycle #e ,,chapter ,,ii ,,description ,,of ,a ,,typical ,,petrol ,,engine-- ,the ,cylinder #h ,,chapter ,,iii ,,engine ,,details-- ,the ,piston #ag ,the ,connecting ,rod #ba ,the ,crankshaft #bc ,the ,flywheel #be ,,chapter ,,iv ,,the ,,valves-- ,poppet ,valves #bi ,sleeve ,valves #ca ,the ,camshafts and ,eccentric ,shafts #cc ,the ,timing ,wheels #cg ,the ,crankchamber #ch ,,chapter ,v ,,the ,,carburettor ,,and ,,carburation-- ,the ,float ,chamber #dd ,the ,petrol ,jet and ,choke ,tube #df ,the ,mixing ,chamber and ,throttle ,valve #dg ,recent ,improvements in ,carburettors #dg ,pressure ,feed and ,gravity ,feed #ej ,,chapter ,,vi ,,ignition ,,and ,,ignition ,,devices-- ,the ,sparking ,plug #ea ,the ,high ,tension ,magneto #eb ,the ,ignition ,coil #eg ,wiring ,diagram for ,magneto ,ignition ,system #fj ,wiring ,diagram for a ,coil ,ignition ,system #fj ,timing the ,ignition #fb ,,chapter ,,vii ,,lubrication-- ,properties of ,oils #fc ,splash ,system of ,lubrication #fc ,improved ,system of ,splash ,lubrication #fd ,forced ,lubrication #fe ,,chapter ,,viii ,,cooling-- ,natural or ,thermo-,syphon ,circulation #fi ,forced or ,pump ,circulation #ga ,,chapter ,,ix ,,the ,,points ,,of ,a ,,good ,,engine-- ,choosing the ,number of ,cylinders #ge ,the ,question of the ,valves #gg ,economy and ,durability #gi ,,chapter ,x ,,two-,,stroke ,,engines-- ,the ,two-port ,two-stroke ,engine #hj ,the 8,kean0 ,duplex ,air ,scavenging ,engine #he ,the ,twin-cylinder ,two-stroke ,engine #if ,,chapter ,,xi ,,horse-,,power ,,and ,,the ,,indicator ,,diagram-- ,work #ih ,power #ih ,brake ,horse-power #ii ,rated ,horse-power #ajj ,indicated ,horse-power #aja ,the ,indicator ,diagram #ajb ,,chapter ,,xii ,,liquid ,,fuels-- ,petrol #ajh ,benzol #ajh ,alcohol #aji ,paraffin #aji ,thermal ,efficiency #aaj ,,appendix ,,engine ,,troubles #aac ,,timing ,,the ,,ignition #aae ,,index #aag ,,list ,,of ,,illustrations ,,fig4 ,,description4 ,,page #a4 ,diagram to explain the meaning of ,suction #a #b4 ,diagram to explain the meaning of ,compression #b #c4 ,otto ,cycle4 ,the ,suction ,stroke #c #d4 ,otto ,cycle4 ,the ,compression ,stroke #d #e4 ,otto ,cycle4 ,the ,power ,stroke #e #f4 ,otto ,cycle4 ,the ,exhaust ,stroke #f #g4 ,general arrangement of a ,modern ,petrol ,engine #i #h4 ,sectional ,drawing of a ,t-headed ,cylinder #ab #i4 ,outside ,view of a ,water-jacketed ,cylinder #ac #aj4 ,stud #ad #aa4 ,bolt #ad #ab4 ,setscrew #ad #ac4 ,motor-cycle ,engine with air-cooled ,cylinder #ad #ad4 ,aeroplane ,engine ,cylinder #ae #ae4 ,cast-iron ,piston #ah #af4 ,method of fixing ,gudgeon ,pin #ai #ag4 ,three forms of ,piston-head #ai #ah4 ,connecting ,rod in the form of a ,stamping #bj #ai4 ,connecting ,rod turned from a solid ,bar of ,steel #ba #bj4 ,crankpin and ,crankwebs #bb #ba4 ,four-throw ,crankshaft #bc #bb4 ,motor-cycle ,crankpin #bd #bc4 ,balanced ,crank #be #bd4 ,sketch showing the unbalanced portion of a ,crank #be #be4 ,balanced ,two-throw ,crankshaft #bf #bf4 ,force acting on a ,flywheel ,rim #bf #bg4 ,built-up ,steel ,flywheel #bg #bh4 ,flywheel turned from a ,steel ,stamping #bh #bi4 ,general arrangement of a ,poppet ,valve #cj #cj4 ,sectional ,drawing of the ,cylinder of a ,sleeve-valve ,engine #ca #ca4 ,sectional ,drawing of the ,cylinder of a ,sleeve-valve ,engine #cb #cb4 ,poppet ,valve-head1 showing ,slot for ,grinding-in purposes #cd #cc4 ,inlet and ,exhaust ,valve ,cams #cd #cd4 ,eccentric ,sheave and ,rod for a ,sleeve ,valve #cf #ce4 ,a ,pair of ,timing ,wheels #cg #cf4 ,a ,crank ,chamber1 outside end view #ci #cg4 ,a ,crank ,chamber1 sectional view #ci #ch4 ,general arrangement of the ,carburetting ,plant #dc #ci4 ,sectional ,drawing of a ,carburettor of the ,jet ,type #dd #dj4 ,plain ,form of the ,choke ,tube #dg #da4 ,petrol ,jet for atomising the ,petrol #dh #db4 ,compensated ,petrol ,jet #dh #dc4 ,automatic ,spring-controlled ,extra-air ,valve #di #dd4 ,plan ,view of ,automatic ,extra-air ,valve #di #de4 ,sectional ,drawing of a ,sparking ,plug #ea #df4 ,a ,sparking ,plug #eb #dg4 ,outside ,view of a ,high-tension ,magneto #eb #dh4 ,view of ,high ,tension ,magneto showing ,distributor and ,contact ,breaker #ec #di4 ,end ,view of ,high ,tension ,magneto #ed #ej4 ,an ,ignition ,coil #ef #ea4 ,an ,ignition ,coil ,case #eg #eb4 ,low ,tension ,contact ,breaker for ,coil ,ignition 7,wipe ,form7 #eh #ec4 ,wiring ,diagram for ,four ,cylinder ,engine with ,magneto ,ignition 7,high ,tension7 #fj #ed4 ,wiring ,diagram for ,four ,cylinder ,engine with ,trembler ,coil ,ignition #fa #ee4 ,improved ,system of ,splash ,lubrication #fd #ef4 ,sectional ,view of ,connecting ,rod end1 showing ,scoop and ,oil ,trough #fe #eg4 ,forced ,lubrication ,system #ff #eh4 ,sectional ,view of ,rotary ,oil ,pump #fg #ei4 ,a ,rotary ,oil ,pump #fg #fj4 ,thermo-syphon ,water ,cooling ,system #fi #fa4 ,forced ,water ,circulation by means of a ,pump #gj #fb4 ,forms of ,water ,piping #gd #fc4 ,two-port ,two-stroke ,engine with ,crankchamber ,compression #ha #fd4 ,diagrammatic ,sketch of a ,duplex ,two-stroke ,air ,scavenging ,engine #hg #fe4 ,general ,arrangement of the 8,kean0 ,two-stroke ,engine #ia #ff4 ,twin-cylinder ,two-stroke ,engine with ,crankchamber ,compression #ig #fg4 ,petrol ,engine ,brake #ajj #fh4 ,force-space or 8,work0 ,diagram #ajc #fi4 ,petrol ,engine ,indicator ,diagram ,four-stroke ,cycle #aje #gj4 ,petrol ,indicator ,diagram for a ,two-stroke ,engine #ajf #ga4 ,diagram of ,valve-setting #aaf ,,preface ,this book deals with principles4 ,there are many books which give a descriptive account of existing types of engines1 but my object in writing this volume has been to assist the reader to obtain thoroughly sound notions of the principles of design and construction which underlie all current practice4 ,if a man understands1 for example1 the construction of the elements of a carburettor and how they ought to perform their several functions1 he should have no difficulty in understanding any special type of carburettor placed upon the market4 ,in dealing with the subject of ignition ,i have purposely avoided any detailed explanation of the manner in which the spark discharge is produced1 because ,i felt that it introduces new ideas and probably causes the reader to lose sight of the fact that the magneto is only1 after all1 an accessory1 although of course a most important one4 ,i hope that the accounts of my experiments with the two-stroke will be of some service to inventors and others2 the many extraordinary breakdowns1 defects and adventures encountered during this period of my career have not been inserted because they would undoubtedly cause the reader to forget1 for the time being1 his fundamental principles4 ,my colleague1 ,mr4 ,oliver ,mitchell1 who lectures at the ,polytechnic on 8,motor ,car ,management and ,inspection10 has read through the proofs for me and very kindly suggested several small additions to the text1 which ,i have incorporated2 he also suggested the insertion of the valve-setting diagram in the ,appendix4 ,my thanks are due to ,mr4 ,mitchell for his services and also to my wife for her assistance in the preparation of the ,index4 ,,francis ,,john ,,kean4 ,,the ,,polytechnic ,,school ,,of ,,engineering1 ,,regent ,,street1 ,,london1 ,w4 ,july1 #aiae4 ,,the ,,petrol ,,engine ,,chapter ,i ,,general ,,principles ,illustration3 ,,fig4 #a4--;,,diagram ,,to ,,explain ,,the ,,meaning ,,of 8,,suction40 ,explosive ,mixtures4--,if a small quantity of liquid petrol or benzol be placed in an open vessel and exposed to a current of air it will quickly disappear or evaporate4 ,we say that the liquid petrol has been vaporized or turned into petrol vapour4 ,a mixture of air and petrol vapour can be ignited and burnt1 the rate of burning being affected by the strength of the mixture4 ,the strength of the mixture is determined by measuring the respective volumes of air and petrol vapour present in a known volume of the mixture4 ,it is possible to form a mixture of air and petrol vapour in such proportions that when ignited by an electric spark it will be completely burnt at such a rate that the combustion is almost instantaneous1 i4e41 it will explode4 ,this mixture of air and petrol vapour would then be referred to as an explosive mixture and would be suitable for supplying to the cylinder of a petrol engine4 ,illustration3 ,,fig4 #b4--;,,diagram ,,to ,,explain ,,the ,,meaning ,,of 8,,compression40 ,the ,meaning of ,suction4--,imagine an iron cylinder ,a 7,fig4 #a7 held down on a rigid base ,c and fitted with a gas-tight piston ,b4 ,if we pull the piston down sharply to the position shown in ,fig4 #b we will realize that there is apparently some force inside the cylinder which is trying to suck the piston up again4 ,the fact that the piston is being withdrawn and no more air or gas admitted above it to fill up the volume it has displaced on its descent causes a partial vacuum in the cylinder4 ,now if by means of a tap or valve of some kind we could put the cylinder in communication with the atmosphere1 air would rush in and fill up the cylinder until the pressure of the gases in it became equal to atmospheric pressure1 when no more air could enter1 because there would be no excess of pressure to force it in4 ,in technical language we would say1 8the piston has sucked in a charge of air0 through the tap or valve4 ,illustration3 ,,fig4 #c4--,,otto ,,cycle4 ,,the ,,suction ,,stroke4 ,the ,meaning of ,compression4--,close the tap or valve and push the piston up again sharply to its original position of ,fig4 #a4 ,you will now encounter considerable resistance and experience a force pushing down against you because you are reducing the volume of the gas and thereby increasing its pressure2 that is to say1 you are compressing the gas1 because you are now making an amount of gas that recently occupied the whole cylinder fit itself into the small space between the top of the cylinder and the crown of the piston4 ,in technical language you would say1 8the piston has now compressed the charge0 of gas within the cylinder4 ,illustration3 ,,fig4 #d4--,,otto ,,cycle4 ,,the ,,compression ,,stroke4 ,the ,meaning1 of a ,stroke4--,in an engine such as is shown diagrammatically in ,figs4 #c and #d1 when the piston ,p moves from its topmost position in the cylinder down to its very lowest position we say it has completed a downstroke1 and when it moves upwards from its lowest to its highest position we say the piston has completed an upstroke4 ,the length of the piston's stroke is equal to twice the length of the crank radius ,r1 and is measured by observing the distance moved by the piston in travelling from its highest position in the cylinder to its lowest or vice versa4 ,the space existing above the piston between it and the cylinder head when the piston has reached its highest position in the cylinder is called the clearance space4 ,it is also referred to as the combustion chamber1 or chamber in which the petrol gas is exploded4 ,when the piston is either at the top or bottom of its stroke the crank radius ,r and connecting rod ,t are in one and the same straight line2 under these conditions we say the crank is on its inner or outer dead-centre4 ,the ,otto ,cycle4--,most petrol engines operate on what is known as the 8,otto0 cycle1 in which the cycle of events is completed once in every four strokes 7or two revolutions7 made by the engine4 ,the 8,otto0 cycle is therefore usually referred to as the four-stroke cycle4 ,in the accompanying diagrams 7,figs4 #c1 #d1 #e1 and #f7 we show in diagrammatic form the interior of a petrol engine cylinder fitted with mushroom type valves4 ,illustration3 ,,fig4 #e4--,,otto ,,cycle4 ,,the ,,power ,,stroke4 ,in studying the figures we assume the engine is being cranked round by hand in the direction of the arrow while we view it from the 8flywheel0 end 7i4e4 the end adjacent to the driver's seat71 then ,a is the pipe which leads the mixture of air and petrol vapour from the carburettor to the cylinder and is called the induction pipe4 ,c is the cylinder1 ,p the piston1 ,i the inlet valve1 ,e the exhaust valve1 ,t the connecting rod1 ,r the crank1 and ,s the sparking plug4 ,the pipe ,b which leads the burnt gases from the exhaust valve to the silencer is called the exhaust pipe4 ,the cycle of operations is as follows3-- ,illustration3 ,,fig4 #f4--,,otto ,,cycle4 ,,the ,,exhaust ,,stroke4 7#a7 ,on the first downstroke made by the piston a suction effect or partial vacuum is produced in the cylinder2 the air and petrol vapour in the induction pipe being at atmospheric pressure1 which is in excess of that now existing in the cylinder1 flow into the cylinder as soon as the inlet valve ,i is opened by the engine mechanism4 ,at the end of this1 the suction stroke1 the inlet valve closes and traps the charge of explosive mixture in the engine cylinder4 ,this is shown in ,fig4 #c4 7#b7 ,on the first upstroke made by the piston the charge of explosive mixture is compressed ready for firing4 ,both valves are shut4 ,this is shown in ,fig4 #d4 7#c7 ,on the second downstroke made by the piston the sparking plug ,s passes a spark which explodes the charge at the very commencement of the downward movement of the piston4 ,the force of the explosion drives the piston downwards1 doing useful work4 ,both valves are shut4 ,this is the power stroke1 and sufficient power must be developed on this stroke not only to do the work required from the engine but also to tide it over the other three idle strokes4 ,on this stroke the piston drives the crank by means of the connecting rod1 but on the other three strokes of the cycle the crank has to drive the piston by means of the power or energy stored in the engine flywheel on the power stroke4 ,towards the end of the power stroke 7or explosion stroke7 the engine mechanism opens the exhaust valve ,e and allows part of the burnt gases to escape to the silencer along the exhaust pipe4 ,this is shown in ,fig4 #e4 7#d7 ,on the second upstroke of the cycle the piston pushes the remaining burnt gases out of the cylinder through the exhaust valve4 ,when the piston reaches the top of its stroke the exhaust valve closes4 ,this is shown in ,fig4 #f4 ,the cycle of operations then begins again1 giving one power stroke and three idle strokes each time as already described4 ,,chapter ,,ii ,,description ,,of ,a ,,typical ,,petrol ,,engine ,for the purpose of explaining the cycle of operations we have considered only a diagrammatic sketch of an imaginary motor-car engine1 but in ,fig4 #g we illustrate an up-to-date motor-car engine4 ,in the first place we note the position and arrangement of the four water-cooled cylinders1 ,a#a1 ,a#b1 ,a#c1 ,a#d1 containing their pistons and mushroom type valves4 ,these are conveniently placed in a vertical position and mounted on top of the crankchamber ,c1 to the bottom of which is attached the oil-base ,b4 ,at the front of the engine are shown the timing wheels in their casing ,e1 and at the rear end the flywheel ,f4 ,the starting-handle connexion is at ,s1 the fan pulley being shown at ,m4 ,the high tension magneto which supplies the current to the sparking plugs is shown at ,h1 and ,i is the induction pipe connected to the carburettor ,k4 ,the water circulating pump is on the off side of the engine and does not appear in the illustration1 but ,l#a is the inlet water pipe leading from the radiator 7not shown7 to the water pump1 and ,l#b is the delivery pipe from the pump to the respective cylinder jackets1 ,l#c being the outlet water pipe4 ,the exhaust pipe is shown at ,d1 and the oil pump at ,p4 ,the valve springs1 valve tappets and guides can also be clearly seen4 ,in examining the several parts of the engine in detail we must not lose sight of their respective positions in the general arrangement view of ,fig4 #g4 ,illustration3 ,,fig4 #g4--;,,general ,,arrangement ,,of ,a ,,modern ,,petrol ,,engine4 ,the ,cylinder4--,probably one of the most important parts of an engine is the cylinder4 ,as we have already seen1 it is inside the cylinder that the charge of petrol vapour and air is exploded and completely burnt4 ,the heat energy of the petrol mixture which is liberated by the explosion is immediately transformed into mechanical work and propels the piston forward like a projectile from a gun4 ,but we must also notice that our present-day arrangements 7clever as they are7 are by no means perfect1 and we cannot1 even under the most favourable circumstances1 convert more than about one-third of the heat energy of the petrol mixture into the mechanical energy of the moving piston4 ,of the remaining two-thirds of the heat1 part is used up in heating the cylinder walls1 the piston and the valves1 and the remainder goes out with the exhaust gases to the silencer1 finally escaping to the outside air4 ,thus two important facts are brought to our notice3-- 7#a7 ,the reason why we use petrol to drive our motor-cars is because petrol 7and certain other liquid fuels such as benzol1 etc47 contains within itself a store of energy which can be liberated as heat when the fuel is burnt or exploded in the presence of air in the engine cylinder4 7#b7 ,at the present day1 even with our most up-to-date contrivances1 we cannot make use of two-thirds of the available heat in our petrol4 ,instead of being able to turn this heat into useful mechanical work1 we are compelled to throw it away--to waste it4 ,further than that1 we have to make special provision to ensure that it shall be wasted as quickly as possible and as easily as possible4 ,we take out the greatest amount that we can possibly turn into work and then hasten to dissipate the remaining two-thirds4 ,we cast hollow chambers on the outside of our cylinders through which we circulate cold water to keep down the heat in the cylinder walls2 if our cylinder walls and piston get too hot our engine may seize up1 therefore we must cool them to ensure satisfactory running4 ,again we make large exhaust valves and provide a free escape through the silencer for the exhaust gases1 so that when we have snatched our useful one-third of the heat supply we may throw the remainder away into the atmosphere as rapidly as possible4--this part is of no use to us1 we cannot turn it into work1 then why let it stay here and heat our cylinder walls and piston still further8 ,it is a good plan to extend this hollow chamber1 containing the water in circulation1 at least round the whole of the combustion chamber and all round the inlet and exhaust valve passages and down the barrel of the cylinder as far as the walls are likely to come into contact with the hot gases from the explosions4 ,we refer to this hollow chamber1 with its circulating water1 as the water-jacket of the cylinder4 ,it is not absolutely essential to have our cylinder water-jacketed1 especially with small engines for motor-cycles and engines for aeroplanes which have revolving cylinders1 but it is practically essential in nearly all other cases4 ,even in the special cases mentioned it is found necessary to form special heat radiating fins on the outside of the heated walls to assist in dissipating or getting rid of the surplus heat and preventing seizure of the piston within the cylinder4 ,these fins are clearly seen on the cylinder of the motor-cycle engine shown in ,fig4 #ac4 ,thus we may say that motor-car engine cylinders are bound to be water-jacketed1 i4e41 to have a hollow space round them containing water in circulation4 ,the cylinders themselves are nearly always made in the form of iron castings and the jacket spaces form part of the cylinder casting as a general rule1 but occasionally the water-jacket space is formed by attaching plates or tubes to the cylinder casting by means of bolts or screws--not an easy thing to arrange successfully1 as it requires water-tight joints4 ,the procedure for manufacturing a motor-car cylinder is first of all to design and calculate the proportions of the various parts and get out a set of working drawings4 ,from these drawings we get patterns and core-boxes made in wood4 ,the patterns are the exact shape of the finished cylinder on the outside1 and the core-boxes are the exact shape of the inside of the finished cylinder 7except in so far as allowance has to be made for parts which must afterwards be machined74 ,the patterns are pushed down into the moulding sand in the foundry1 and when withdrawn leave their impression1 thus forming moulds4 ,the core-boxes are filled with sand1 which when withdrawn furnishes us with masses of sand that are the counterpart of the interior of the cylinder in shape4 ,these cores are supported centrally in the mould 7which is usually in halves1 or more than two parts71 while the molten iron is poured into the intervening space to form the iron casting4 ,when the casting has cooled down the sand can be cleaned off quite easily4 ,one set of patterns and core-boxes will thus produce quite a number of cylinder castings1 each being similar in every respect to the other1 the process being a quick and fairly cheap method of reproduction4 ,later on the cylinder barrel has to be machined and bored out true to very fine limits by the use of boring tools and some kind of boring machine or lathe4 ,the flanges or flat faces have to be planed true in a planing machine and the valve stem guides and valve seatings must be carefully and truly machined to correct size and shape4 ,illustration3 ,,fig4 #h4--,,sectional ,,drawing ,,of ,a ,t-,,headed ,,water-,,jacketed ,,cylinder4 ,,valves ,,on ,,opposite ,,sides ,,of ,,cylinder4 ,illustration3 ,,fig4 #i4--,,outside ,,view ,,of ,a ,,water-,,jacketed ,,cylinder4 ,figs4 #h and #i show two views of a single motor-car engine cylinder1 the water-jacket forming part of the cylinder casting4 ,in the figures ,c is the cylinder barrel or bore2 ,j the water-jacket2 ,i the inlet for the jacket water2 ,o the outlet for the jacket water2 ,d is for the compression tap2 ,s for the sparking plug2 ,v#a1 ,v#b are the valve seats2 ,g#a1 ,g#b are the valve stem guides2 ,h#a1 ,h#b are caps which may be removed when the valves are being put in or taken out2 f#a1 f#b1 f#c1 f#d1 f#e are called flanges4 ,the flange f#a is used for attaching the cylinder to the crankchamber2 while it is quite true that the force of the explosion within the cylinder drives the piston downwards1 it is equally true that it also tends to force the cylinder head off or to blow the cylinder casting upwards off the crankchamber1 unless it is securely fastened to it by means of screws or bolts passing through the flange f#a4 ,the flanges1 f#b1 f#c are for the inlet and outlet water pipe attachments1 and f#d1 f#e are for the induction pipe and exhaust pipe connexions4 ,generally the pipes will have flanges and be held tight against the flanges on the cylinder casting by means of screws or studs4 ,figs4 #aj1 #aa1 and #ab show how two metal flanges are held in contact by means of screws or studs or bolts1 and they also show the packing materials between the metal surfaces which keep the joint tight and prevent water or gas leaking across the flanges and escaping to the outside air1 or air leaking in if the internal pressure is below that of the atmosphere4 ,illustration3 ,,stud ,,fig4 #aj4 ,illustration3 ,,bolt ,,fig4 #aa4 ,illustration3 ,,setscrew ,,fig4 #ab4 ,illustration3 ,,fig4 #ac4--,,motor-,,cycle ,,engine ,,with ,,an ,l-,,headed ,,air-,,cooled ,,cylinder4 ,,valves ,,both ,,on ,,same ,,side ,,of ,,cylinder4 ,illustration3 ,,fig4 #ad4--,,sectional ,,drawing ,,of ,a ,,built-,,up ,,cylinder ,,suitable ,,for ,,an ,,aeroplane ,,engine4 ,in ,figs4 #h and #i the valves are placed one on each side of the cylinder1 this form of cylinder being known as a ,t-headed cylinder1 but it is rather more usual here in ,england to place both valves on the same side of the cylinder and next to each other as indicated in ,fig4 #ac1 this form of cylinder being known as an ,l-headed cylinder4 ,the chief object is of course to avoid the use of two valve shafts and also to produce a neater looking engine1 but the ,t-headed design is better cleaned or scavenged by the passage of the inlet and exhaust gases4 ,when a motor-car engine has two cylinders we frequently find them both in a single casting1 having a common water-jacket1 and then we say they are cast in pairs4 ,a four-cylinder engine may thus have3 7#a7 ,cylinders cast separately2 7#b7 ,cylinders cast in pairs2 7#c7 ,cylinders cast en bloc2 or all four in a single large casting4 ,the third method is cheapest in first cost1 but in the event of breakage will become the most expensive4 ,the second method is a sound compromise4 ,an example of a built-up cylinder and water-jacket is shown in ,fig4 #ad1 the cylinder barrel being of steel tube with steel flanges1 and the water-jacket being formed by copper tube slipped over the outside of the steel cylinder4 ,its great advantage lies in the reduction of weight1 and it is thus largely used for aeroplane work4 ,the valves would then be fitted in the top cover of the cylinder and driven by overhead gearing4 ,,chapter ,,iii ,,engine ,,details ,the ,piston is perhaps the most important detail to consider1 for it is on the piston that the force of the explosion acts when the heat energy is converted into mechanical energy4 ,it must be made sufficiently strong to withstand the bursting effect of successive explosions1 and yet if we make the metal too thick it will retain too much of the waste heat and the piston may seize in the cylinder due to expansion4 ,to understand why the piston is likely to seize in the cylinder we have only to remember that when a metal body is heated it gets larger in every direction1 but if cooled it returns to its original size4 ,now if we make the metal of the piston too thick so that the waste heat cannot pass quickly through it and dissipate itself at cooler parts of the engine1 then the bulk of this heat will be concentrated in the piston head1 causing it to expand and become a tight fit in the cylinder1 as the cylinder walls are fairly thin and in contact with the jacket water which keeps them fairly cool and prevents them expanding much above their normal size4 ,the actual amount of expansion is very small of course1 but there is very little clearance between the piston and the cylinder walls1 even when the engine is all cold--perhaps five-thousandths of an inch4 ,the piston therefore must be strong1 yet as light as we can make it1 having regard to the necessity for its being amply stiff and rigid and able to stand up to its work4 ,illustration3 ,,fig4 #ae4--,,two ,,views ,,of ,a ,,cast ,,iron ,,piston ,,with ,,gudgeon ,,pin ,,and ,,packing ,,rings4 ,generally it will be an iron casting in the form of a small cylinder 7see ,fig4 #ae71 having provision in it for the packing rings ,p1 and the gudgeon pin ,g1 with its fastening screws ,s#a1 ,s#b4 ,the piston itself1 as we have observed1 must be a nice sliding fit in the bore of the cylinder without any shake or side play when there are no packing rings in the grooves4 ,the packing rings are turned to size so as to fit the cylinder exactly and prevent any gas leaking past the piston into the crankchamber4 ,these rings are very light1 are made from cast iron1 and arranged to break joint1 as indicated1 by cutting the middle ring in the opposite direction to the two outer ones4 ,bosses are cast on the inside of the piston and afterwards bored out to receive the steel gudgeon pin or wrist pin ,g4 ,this pin is best made of plain parallel cylindrical form ground true1 and the bosses in the piston should be reamered out to the exact size of the pin4 ,when the pin has been inserted the tapered screws are screwed hard up by means of a special spanner and bear against the pin1 preventing it from coming loose or from shaking or knocking4 ,there are many other methods of fixing the gudgeon pin which are not shown here2 each has some special point in its favour1 but the one illustrated is undoubtedly the best and affords a positive adjustment for wear4 ,illustration3 ,,fig4 #af4--,,method ,,of ,,fixing ,,the ,,gudgeon ,,pin ,,which ,,allows ,,for ,,adjustment ,,after ,,wear4 ,illustration3 ,,fig4 #ag4--,,three ,,forms ,,of ,,piston ,,head4 ,an enlarged view of one of the bosses1 showing the taper pin in detail and how the split pin ,q prevents it from slacking back by contact with the wall of the piston1 is shown in ,fig4 #af4 ,sometimes the lower part of the piston is made lighter by drilling holes through the walls4 ,it is very important to reduce the weight of the piston as much as possible1 otherwise the engine cannot attain a high speed1 so that it becomes essential to bear this in mind when constructing engines for racing purposes4 ,frequently we find steel pistons used1 as they may be made lighter for the same strength1 and then steel piston rings may be used2 they are not much in favour for ordinary motor-car engines because the steel pistons expand at a greater rate than the cast iron of the cylinder1 so that there is more liability to seizure4 ,the crown of the piston is sometimes curved upwards and at other times curved downwards1 but more often it is flat as shown in ,fig4 #ag4 ,the gudgeon pin is sometimes made of mild steel1 and the surface is then case-hardened in the centre where the connecting rod end bears4 ,at the present time it is quite as common to find gudgeon pins made of special nickel steel or other steel alloys that do not require case-hardening4 ,on the whole these special steels make the best gudgeon pins and stand the hardest wear4 ,illustration3 ,,fig4 #ah4--;,,connecting ,,rod ,,in ,,the ,,form ,,of ,a ,,phosphor ,,bronze ,,stamping4 ,the ,connecting ,rod is another very important detail of the engine mechanism1 its function being to transmit the force of the explosion from the piston to the crankshaft4 ,illustration3 ,,fig4 #ai4--,,steel ,,connecting ,,rod ,,turned ,,out ,,of ,,the ,,solid ,,bar4 ,one end of the connecting rod moves up and down with the piston and oscillates 7or swings to and fro7 on the gudgeon pin1 while the other end of the connecting rod travels in a circle1 being pivoted at the crankpin and rotating in a circle which has for its centre the centre line of the engine crankshaft4 ,this is clearly indicated in ,fig4 #ah4 ,on the suction stroke of the engine the piston has to be pulled down1 as we have already seen2 on the explosion stroke the greatest pressure acts on the piston and pushes the connecting rod down4 ,thus sometimes the connecting rod is being pulled and at other times it is being pushed2 in each case it has to overcome the resistance of the engine and drive the car4 ,it is evident1 therefore1 that the character of the load carried by a connecting rod is just about as complex and dangerous as it is possible for a system of loading to be1 and great care has to be taken in the design of such rods to ensure adequate strength without undue weight1 as this would tend to keep down the maximum speed of the engine4 ,another important consideration is the cost of production1 and for this reason one often finds it in the form of a phosphor bronze stamping of ,i section1 although the ideal form is a round section of steel with a straight taper from gudgeon pin to crankpin end1 and having a hole bored right up the centre to reduce the weight without sacrificing much strength4 ,when the rod is made in the form of a stamping between dies it is possible to turn out great quantities at very low cost and at a very rapid rate1 whereas the round steel rods would require to be machined from the solid bar to compete in price with the others4 ,when phosphor bronze is used it is only necessary to bore out carefully and face the bearings at the two ends for the gudgeon pin and crankpin2 the bearing at the crankpin end is always formed with a removable cap to facilitate fitting it nicely to the crankpin1 journal and also to allow for adjustment as the bearing wears4 ,with steel rods it is necessary to cast a white-metal lining in the crankpin end and then bore it out to form the bearing1 but the crosshead bearing is usually formed by a phosphor bronze bush4 ,it is evident1 therefore1 that the steel rods are more expensive1 but they make a splendid mechanical job4 ,a steel connecting rod is shown complete in ,fig4 #ai4 ,stamped steel rods of ,i section are also commonly used and are much better and stronger than those made entirely of phosphor bronze4 ,illustration3 ,,fig4 #bj4--;,,crankpin ,,and ,,crankwebs4 ,illustration3 ,,fig4 #ba4--;,,four-,,throw ,,crankshaft ,the ,crankshaft1 as its name implies1 is a shaft with one or more cranks or right-angled bends in it4 ,its function is to convert the sliding motion of the piston into the rotary motion of the flywheel and revolving shaft4 ,a crankshaft with a single throw 7or single crank7 is shown in ,fig4 #bj2 a four-throw crankshaft is shown in ,fig4 #ba2 and ,fig4 #bb shows how an equivalent motion can be obtained by a single pin fixed into the face of a flywheel4 ,this device 7,fig4 #bb7 is frequently used for motor-cycle engines4 ,crankshafts are always made of steel2 sometimes mild steel is used1 but more usually special alloys of steel containing chrome1 nickel1 vanadium1 etc41 are used4 ,the general practice at the present time is to machine the crankshaft direct out of a solid bar of steel2 this requires special jigs for holding the work and special tools for cutting the metal1 but is the quickest1 cheapest1 and most satisfactory method to adopt4 ,a few firms specialize in this class of work with high-grade steel and can supply crankshafts from stock4 ,illustration3 ,,fig4 #bb4--,,motor-,,cycle ,,crankpin ,,fixed ,,into ,,the ,,flywheel4 ,it is easily seen by examining ,fig4 #ah that the crankshaft is being twisted in overcoming the engine resistance1 while ,fig4 #bj shows that the crankshaft is being bent under the push from the connecting rod1 so that we say the material of a crankshaft is subjected to combined bending and twisting1 and as such a combination is not easy to resist we see now why special steel alloys are required for safety1 combined with economy in material and reduction of weight4 ,in ,fig4 #bj the crankpin is shown at ,a1 the crank cheeks or webs at ,b#a1 ,b#b and the crankshaft proper at ,c4 ,the portions of the crankshaft ,c which work in the bearings ,d#a1 ,d#b are termed journals4 ,a crankshaft must be very stiff and not bend or twist sensibly1 otherwise the shaft will vibrate when the engine runs up to speed--which would be very undesirable4 ,it must be perfectly true with all the bearings absolutely in line and the journals well bedded down in their respective brasses 7or bearings71 otherwise mechanical troubles will arise4 ,each crank with its crankpin and webs forms a lop-sided or unbalanced mass1 so that either 7#a7 each crank must have its own balance weight as in ,fig4 #bc1 or 7#b7 special balancing masses must be fitted at each end of the crankshaft4 ,a convenient method of balancing the crankshaft is to have a fan pulley at one end and the flywheel at the opposite end1 so that by drilling holes in the faces of these discs an amount of metal may be removed from them sufficient to balance the excess weight of the respective crankpins and webs4 ,in ,fig4 #bd the shaded area indicates that portion of the crank which constitutes an unbalanced mass4 ,crankshafts for high-speed engines have always to be very carefully balanced1 otherwise the engines will never run satisfactorily1 the want of balance being greatly aggravated as the speed of rotation increases4 ,fig4 #be shows how the crankshaft of a two-cylinder engine may be balanced by drilling holes in the flywheel and fan pulley respectively1 but the same effect may be produced by attaching balancing masses--this latter method would1 however1 be more inconvenient and expensive4 ,the crankpins and journals are ground truly circular after being turned in the lathe as true as possible4 ,illustration3 ,,fig4 #bc4--,,sketch ,,of ,a ,,balanced ,,crank4 ,illustration3 ,,fig4 #bd4--,,sketch ,,showing ,,the ,,unbalanced ,,portion ,,of ,,the ,,crank ,,by ,,shaded ,,lines4 ,illustration3 ,,fig4 #be4--,,two-,,throw ,,crankshaft ,,balanced ,,by ,,drilling ,,holes ,,in ,,flywheel ,,and ,,fan ,,pulley4 ,illustration3 ,,fig4 #bf4--,,sketch ,,to ,,illustrate ,,the ,,forces ,,acting ,,on ,a ,,flywheel ,,rim4 ,the ,flywheel4--,we have already described how the force driving the piston of a motor-car engine varies during the four strokes of the cycle1 but we must note that it also varies considerably during each individual stroke4 ,thus1 on what is known as the explosion stroke 7or power stroke7 of the cycle1 the pressure at the commencement of this stroke may be exceedingly great and yet towards the end of the stroke the gases have expanded and the exhaust valve has been opened1 so that the pressure acting on the piston is then very small4 ,again1 on the compression1 suction1 and exhaust strokes1 the piston has to be pushed or pulled by some means1 as no power is being generated4 ,therefore1 if the engine is to be self-acting and run continuously1 some means must be provided for storing up the great force of the explosions and giving it out again on the idle strokes4 ,the function of the flywheel is to store any energy given to it over and above that required to drive the car and to give it out again when required for performing the functions of compressing1 exhausting1 and sucking in gas1 as well as to keep the car running steadily4 ,it is simply a heavy wheel mounted on the end of the crankshaft which1 when once started revolving at a high speed1 is not easily stopped1 and which will give up part of its energy each time its speed is reduced owing to the demands of the engine2 but when the engine is generating power the wheel will speed up and store the excess--the mere fact that the wheel is heavy causes these changes in speed to occur slowly1 and therefore on the whole the fluctuation of speed is not great when a suitable flywheel is fitted4 ,the flywheel does not limit the maximum speed of the engine1 as it could go on slowly increasing in speed if no resistance was encountered until the wheel finally burst or flew to pieces4 ,thus the flywheel does not regulate the speed of the engine2 it merely smooths out the inequalities in the several strokes of the 8cycle40 ,flywheels of motor-car engines are now always made of steel1 so that they can be safely run at speeds up to #c1jjj revolutions per minute without fear of the rim bursting4 ,all parts of the rim tend to fly off radially in the direction of the arrows as shown in ,fig4 #bf under the action of centrifugal force4 ,a built-up flywheel is shown in ,fig4 #bg1 and one made from a single stamping of steel is shown in ,fig4 #bh4 ,generally speaking1 when a coned clutch is fitted one portion of it is formed on the inside of the flywheel rim as indicated in these two figures4 ,when the construction shown in ,fig4 #bh is adopted the lining would be inserted after the clutch cone had been put into place2 very often the lining is made up of sections which can be readily inserted or withdrawn after the cone is in position4 ,illustration3 ,,fig4 #bg4--;,a ,,flywheel ,,built ,,up ,,from ,,steel ,,forgings4 ,illustration3 ,,fig4 #bh4--;,a ,,flywheel ,,turned ,,from ,a ,,steel ,,stamping4 ,,chapter ,,iv ,,the ,,valves ,poppet ,valves4--,valves are provided for the purpose of controlling the admission of the mixture to the cylinder and also for controlling the exhaust or ejection of the burnt gases at the end of the firing stroke4 ,the most common form of valve is the mushroom or poppet type of valve shown in ,fig4 #bi1 in which ,a is the valve head1 ,b is the valve stem1 ,c is the valve seating1 and ,d is the cotter hole for the cotter ,e4 ,it will be seen that the general appearance of the valve is a disc of steel with a fine stem to it similar to a mushroom in general outline--hence its name4 ,the valve has a coned face which is kept pressed down on a coned seating by means of the pressure of a powerful spring ,f acting on the washer ,g1 which bears against the cotter ,e and thus presses down the valve stem4 ,to ensure that the valve shall always come down correctly on its seating and make a gas-tight joint1 the valve stem guide ,m is provided4 ,illustration3 ,,fig4 #bi4--;,,general ,,arrangement ,,of ,a ,,poppet ,,valve 7,a7 ,,with ,,tappet 7,k7 ,,and ,,cam 7,h74 ,the cam ,h raises the valve off its seat at the required instant when the motion of the camshaft brings the cam under the roller ,r4 ,the cam lifts the roller vertically and with it the tappet or push rod ,k1 which slides vertically upwards in the guide ,p and lifts the valve4 ,the tappet is provided with an adjustable head ,s kept in position by the locknut ,t4 ,to adjust the clearance between the head of the tappet and the underside of the valve stem the locknut ,t must first be slackened back and then the head ,s can be screwed up or down as desired1 the best clearance being about #a_/fd of an inch2 the locknut is then tightened down again4 ,during this operation the valve must be down on its seat4 ,sometimes to reduce the noise arising from the tappet striking the valve stem1 the head of the tappet is padded with some material such as hard vulcanite fibre1 but this wears down more quickly than steel and requires frequent adjustment4 ,the latest device for reducing the noise arising from the valve mechanism consists in totally enclosing the valve gear and springs either by metal plates bolted to the cylinder casting or by extending the crankchamber to cover it all in1 and then it is certain to be well lubricated4 ,the exhaust valve is always liable to give trouble either from leakage or seizure or other causes due to the great heat of the exhaust gases1 so that the valves are often made now of tungsten steel alloy which is not much affected by heat4 ,if a mushroom type valve leaks it can be ground in and made a tight fit on its seating1 provision usually being made for this in the form of a slot cut in the valve head1 as shown in ,fig4 #cb1 for the insertion of a screwdriver or special tool4 ,to grind in a valve1 remove the cap ,q by unscrewing it1 raise the spring ,f by pushing up the washer ,g and then withdraw the cotter ,e4 ,lift out the valve and smear the coned face with fine emery powder and oil 7or water74 ,put the valve back and turn it to and fro on its seating by means of the screwdriver1 keeping a firm pressure down on it2 continue the operation until by examining the valve you ascertain that it touches on the seating all the way round1 then couple up the spring again1 after carefully removing all traces of the emery powder4 ,illustration3 ,,fig4 #cj4--,,sectional ,,drawing ,,of ,,the ,,cylinder ,,of ,a ,,sleeve ,,valve ,,engine1 ,,with ,,inlet ,,forts ,,uncovered4 ,illustration3 ,,fig4 #ca4--,,sectional ,,drawing ,,of ,,the ,,cylinder ,,of ,a ,,sleeve ,,valve ,,engine1 ,,with ,,exhaust ,,ports ,,uncovered4 ,sleeve ,valves4--,another form of valve which has come very much into favour is the sleeve valve1 two views of which are shown in ,figs4 #cj and #ca4 ,in this case the gases enter the cylinder through ports or slots ,p cut in the cylindrical cast iron sleeves ,s#a1 ,s#b1 which are placed between the piston ,k and the walls of the water-jacketed cylinder ,c4 ,these sleeves are moved up and down inside the cylinder1 while the piston travels up and down inside the inner sleeve ,s#b just as though it constituted the cylinder ,c4 ,some engines have two sleeves1 as shown in the figure1 but others have only one sleeve1 and there is very little to choose between the two types on the score of efficiency4 ,the great claim made for the sleeve valve is that it is almost noiseless in action and gives very much fuller openings for inlet and outlet of the gases4 ,the piston has the usual number of packing rings to keep it gas-tight1 and there is also a deep packing ring provided in the head of the cylinder ,h to keep the sleeve ,s#b gas-tight and prevent loss of compression pressure4 ,the head of the cylinder is usually detachable1 and has often separate water connexions in the form of pipes leading from the cylinder jackets4 ,the sleeves receive their reciprocating motion from eccentrics and rods attached to pins shown at the bottom right-hand corner of each sleeve4 ,it might be expected that the sleeves would get very hot or very dry and seize up1 or the piston might seize1 but in actual practice this has not occurred to any great extent1 and on the whole they have been very successful4 ,it is1 however1 necessary to keep the engine well lubricated1 especially when the sleeves get worn1 as the oil prevents loss of gas by leakage past the sleeves and piston4 ,in ,fig4 #ca the two sleeves have come together in such a position that the ports coincide with the exhaust ports cut in the cylinder walls and therefore the exhaust is full open1 and as the sleeves travel at times in opposite directions quick opening and closing of the ports is secured4 ,the cylinder head is held down to the cylinder casting by screws or bolts and can be readily detached for cleaning or inspecting the interior of the cylinder4 ,the great objection raised against the sleeve valves is their excessive weight and the unmechanical manner in which they are operated4 ,illustration3 ,,fig4 #cb4--,,sketch ,,showing ,,slot ,,in ,a ,,poppet ,,valve ,,head ,,for ,,grinding-,,in ,,purposes4 ,illustration3 ,,fig4 #cc4--;,,inlet 7,a7 ,,and ,,exhaust 7,b7 ,,valve ,,cams ,,for ,a ,,slow-,,running ,,petrol ,,engine4 ,the ,camshafts and ,eccentric ,shafts4--,these are usually made from the same material as the crankshaft and machined from the solid bar1 the projecting cams or eccentrics being afterwards cut to the correct shape4 ,in the case of a camshaft it is very important that the shape of the cams should be such that they lift the valves quickly off their seats to the full extent of their opening 7or lift71 keep them open for as long a period as desirable1 and then allow them to close quickly but without shock4 ,cams which have straight sides are more in favour than those with curved sides1 but if the action of the cams is to be theoretically correct the side of the cam should be curved in such a manner that the valve is lifted at first with a uniformly increasing speed and afterwards with a uniformly decreasing speed1 so that it will be at rest in its top position4 ,if this is not done the valve tappet may jump a little above the cam each time the valve is lifted4 ,in ,fig4 #cc the cam ,a is intended for the inlet valve and the cam ,b for the exhaust valve1 the essential difference being that the exhaust valve must be kept open longer than the inlet valve1 and therefore the exhaust valve cam is the wider of the two4 ,the timing of the inlet and exhaust valves of an up-to-date engine may be explained by considering the crankpin circle as divided into #cfj parts or degrees4 ,if there were no lag or lead in the opening of the valves1 then they would open when the crank was on its dead-centre and close when the crank was on its dead-centre4 ,the inlet valve would open when the crank was on its top dead-centre and close when it had reached its bottom dead-centre1 this representing the suction stroke of the engine4 ,then would follow compression and explosion1 giving two strokes or one revolution before the exhaust valve commenced to open4 ,the exhaust valve would then open when the crank was on its bottom dead-centre and close when the crank reached its top dead-centre corresponding to the completion of the exhaust stroke4 ,it is very important that the pressure of the gases above the piston when it commences to move upwards on the exhaust stroke should be as low as possible1 and this can only be secured by opening the exhaust valve towards the end of the explosion or power stroke1 thus allowing the bulk of the gases to escape and leaving the piston with little resistance to encounter on its upward exhaust stroke4 ,therefore we give the exhaust valve a lead of about #cj degrees1 which means that it begins to open when the engine crank is #cj degrees from the bottom dead-centre on the downward explosion stroke1 and we give it a lag of about #e degrees in closing4 ,this means that we keep the exhaust valve open until the crank has moved #e degrees over the top centre1 so that we may fully utilize the momentum of the gases to clear out the cylinder or scavenge it4 ,as the piston moves rapidly up the cylinder on the exhaust stroke it pushes the gases in front of it out through the exhaust opening1 but when it gets to the top of its stroke the piston stops and then comes down again for the suction stroke1 whereas the gases will tend to keep on moving if they are not unduly restricted in their passage through the exhaust system1 so that we can generally obtain some slight advantage by giving the exhaust valve a small amount of lag in closing4 ,the pressure of the gases in the cylinder after the exhaust valve closes will nearly always be a little above atmospheric pressure1 and therefore nothing is gained by opening the inlet valve immediately the exhaust closes--we generally allow an interval of #e degrees1 which means that the total lag of the inlet valve is #aj degrees in opening1 or the inlet valve does not begin to open until the crank has moved #aj degrees off its top dead-centre on the downward suction stroke4 ,at the end of the suction stroke the piston will again come to rest before moving up on the compression stroke1 but the gases will continue to rush into the cylinder from the carburettor owing to their momentum if we leave the inlet valve open a little longer1 hence we generally give it a lag of #bj degrees in closing1 which means that the inlet valve does not close until the crank has moved #bj degrees up from the bottom dead-centre on the compression stroke4 ,illustration3 ,,fig4 #cd4--;,,eccentric ,,sheave 7,a7 ,,and ,,eccentric ,,rod 7,b7 ,,for ,,operating ,a ,,sleeve ,,valve4 ,the camshaft requires to be well supported in bearings to prevent it from sagging or bending under its load4 ,if the shaft and the cams are not made from nickel steel or high-grade steel alloy1 they require to be case-hardened 7hardened on the surface7 to prevent wear on the surfaces due to the pressure of the valve springs1 which is considerable and may reach #ajj lb4 per valve easily2 the same applies to the rollers of the tappets4 ,when sleeve valves are fitted to the engine1 eccentric sheaves must be used instead of cams1 as no springs are employed4 ,an eccentric sheave with its strap and rod are shown in ,fig4 #cd4 ,the valve shaft or lay shaft is shown at ,c1 and the sheave with the hole bored eccentrically is shown at ,a1 and ,b is the combined eccentric strap and rod4 ,the pin ,d operates the sleeve valve1 giving it a reciprocating motion in a vertical direction1 the angular movement being taken up by the oscillation of the rod about the pin ,d1 which would be fixed into the sleeve4 ,sometimes a groove is formed round the periphery of the eccentric disc or sheave to keep the strap in position and prevent end movement4 ,as the weight of the sleeves is very considerable1 the pin ,d and the eccentric rod must be well proportioned to prevent breakage or undue wear4 ,illustration3 ,,fig4 #ce4--;,a ,,pair ,,of ,,timing ,,wheels4 ,the ,timing ,wheels4--,as there is only one suction stroke and one exhaust stroke in every two revolutions of the engine crankshaft1 it will be clear that the camshaft or eccentric shaft must be driven at half the speed of the engine crankshaft4 ,this may be done by the use of two gear wheels or wheels having teeth cut on their periphery1 such wheels when used for this purpose being called timing wheels1 because the positions of the cams on the camshaft 7or the eccentrics on the eccentric shaft7 relative to the engine crankshaft when the teeth of the timing wheels are put into mesh determines the timing of the inlet and exhaust valves1 i4e41 the instant at which they will open or close4 ,a pair of timing wheels is shown in ,fig4 #ce4 ,the pinion ,a has twelve teeth and is keyed to the engine crankshaft1 but the wheel ,b1 which is keyed to the valve shaft1 has twenty-four teeth1 and hence the valve shaft runs at half the speed of the crankshaft4 ,the wheels shown are spur gears1 and the teeth run straight across the rim of the wheel2 it is1 however1 quite common to find wheels with curved or helical teeth1 as these run quieter4 ,sometimes when spur gearing is used1 one of the wheels is made of fibre and the other of steel1 but when helical gears are used the wheels are generally made from nickel steel of high tensile strength4 ,the finer the pitch of the teeth 7i4e4 the distance between the centres of consecutive teeth7 the quieter the gears will run1 but the question of strength and the cost of production must also be considered4 ,the latest practice is to use a silent chain drive2 this originated with the introduction of the sleeve valve and eccentric shaft4 ,when chains are used for the timing wheels provision must be made for taking up slack in the chain owing to stretching of the links1 and as this cannot be done in the usual manner 7by sliding the sprocket wheels further apart7 owing to the centres of the crankshaft and the valve shaft being rigidly fixed by the bearings1 a small jockey pulley 7with teeth on it similar to those on the chain sprocket wheels7 is provided attached to a short shaft or spindle1 which can be raised or lowered at will1 and thus keep the correct tension on the chain4 ,the chain drive must be more expensive and require more attention2 moreover1 it cannot be so very much quieter in action than good well-cut helical gearing4 ,illustration3 ,,fig4 #cf4 ,illustration3 ,,fig4 #cg4 ,,two ,,views ,,of ,a ,,crankchamber4 ,the ,crankchamber4--,the crankchamber1 as its name implies1 is the receptacle which contains and supports the crankshaft and also the camshaft4 ,it is generally an aluminium casting1 but frequently for commercial vehicle engines the top portion is made of cast iron and the bottom portion of sheet steel4 ,in either case brass or gunmetal bearings1 often lined with white metal1 are fitted for the shafts to revolve in1 and the engine cylinders are mounted on the top of the chamber4 ,provision should be made on the sides and ends of the crankchamber for fitting the magneto and oil pump and also the water pump1 if required4 ,there must also be some form of housing or extension of the chamber to enclose the timing wheels1 and sometimes the whole of the valve gear is contained within the crankchamber to ensure proper lubrication for it and stop any noise from it reaching the outside world4 ,it is also important that there should be large inspection openings fitted with proper oil-tight covers and some provision for easily pouring large quantities of oil down into the lower portion of the chamber4 ,the design of a crankchamber necessitates careful forethought to ensure ample provision for all the necessary attachments and fittings and to secure the maximum accessibility of all parts4 ,one or two vent pipes1 consisting of upwardly projecting pipes having their outer end covered with wire gauze and screened from dust should be provided to allow hot air and gas to escape from the chamber4 ,two views of a crankchamber of modern design are shown in ,figs4 #cf and #cg4 ,in these figures ,a is the top half of the crankchamber which rests upon the chassis or framework of the car1 being bolted to an underframe at ,b and ,c4 ,the cylinders are attached to the chamber at the flange ,h by means of studs and nuts4 ,this portion1 the top half of the crankchamber1 requires to be very strong and stiff1 because the upward pressure of the explosions acts on the crown of the cylinder and tends to tear the cylinder off the flange ,h1 while at the same time it exerts a great force on the piston1 pushing it downwards and tending to force the crankshaft down out of its bearings4 ,in the best practice the whole weight of the crankshaft is supported from the top half of the crankchamber and is carried on the bearing bolts as shown at ,s1 so that they also receive the downward thrust of the piston and in their turn transmit it to the main casting4 ,the bottom half of the crankchamber then becomes merely an oil container1 or reservoir1 and dust cover2 it should be so arranged and situated that it may be readily removed for inspection of shaft and bearings from underneath4 ,sometimes the crankchamber has long arms1 which can be attached directly to the side members of the chassis1 or it may be supported in the chassis by a tubular cross member4 ,in ,fig4 #cg the camshaft is shown at ,t2 the magneto would be carried on the bracket ,e and driven by gearing from the crankshaft4 ,the facing at ,g is for the water pump1 which1 in this case1 is intended to be mounted on an extension of the camshaft ,t4 ,the oil pump would be fixed at ,f1 preferably towards the rear of the engine1 so as to secure an adequate supply of oil for the pump when the car is climbing a steep hill4 ,the oil could be drawn off and the reservoir emptied by unscrewing the large plug shown in the centre of ,d in ,fig4 #cg4 ,the timing wheel housing or casing is shown at ,q2 the oil ducts and connexions for supplying the main bearings with oil are not shown in these drawings1 nor are the inspection openings and covers4 ,the upper half of the crankchamber frequently becomes very hot1 due to conduction of heat from the metal of the cylinders1 and for this reason it has from time to time been proposed to draw the air supply of the carburettor through the crankchamber to serve the dual purpose of cooling the bearings and heating the air supply to the carburettor2 but the idea has not found favour1 as there is considerable risk of dust and grit finding its way into the bearings and causing trouble due to abrasion4 ,,chapter ,v ,,the ,,carburettor ,,and ,,carburation ,a carburettor is a contrivance for supplying an explosive mixture of air and petrol vapour to a petrol engine4 ,petrol1 although a liquid fuel1 is a combination of carbon and hydrogen which1 when supplied with the necessary air1 can be burnt and thus evolve heat1 which heat is turned into work inside the engine cylinder4 ,what we have to supply to the engine is really a mixture of air and petrol vapour in certain proportions1 such a mixture being often spoken of as carburetted air on account of the carbon contained in it4 ,about two parts of petrol vapour 7by volume7 are required to every one hundred parts of mixture1 or fifteen pounds of air to every pound of petrol vapour 7by weight74 ,this carburetted air must be of the required strength and form a homogeneous mixture in the form of a vapour4 ,the problem of carburation consists in forming a mixture of the correct strength and character4 ,air may be carburetted by passing it over the surface of liquid petrol in a surface carburettor1 or by drawing it over or among wicks saturated with liquid petrol as in the wick type of carburettor1 but both these methods have been largely superseded by the use of what is now known as a jet or spray type of carburettor1 in which the petrol is sprayed from a fine jet and mixes with air which is passing up rapidly round the outside of the jet4 ,in all cases1 however1 the liquid petrol must be vaporized before entering the engine1 and to do this heat must be supplied to the mixture1 just as water has to be heated before it can be vaporized and turned into steam4 ,under ordinary circumstances sufficient heat can be obtained from the incoming air to effect vaporization of the liquid petrol if it issues in the form of a very finely divided spray1 but when the demand for mixture1 from the engine1 is great the air cannot supply the requisite heat without its temperature falling below the vaporization point2 hence most carburettors of up-to-date pattern are fitted with a mixing chamber surrounded by a hot-water jacket4 ,the essential features of the carburetting plant are shown diagrammatically in ,fig4 #ch1 in which ,a is the petrol tank fitted with the petrol tap ,g1 to which is coupled the petrol pipe ,f4 ,some form of petrol filter as indicated at ,b should be placed between the tank and the carburettor ,c4 ,the throttle valve of the carburettor is shown at ,h1 the extra-air valve at ,e1 and the engine induction pipe at ,d4 ,illustration3 ,,fig4 #ch4--;,,general ,,arrangement ,,of ,,the ,,carburetting ,,plant1 ,,showing ,,petrol ,,tank 7,a71 ,,petrol ,,filter 7,b71 ,,carburettor 7,c71 ,,and ,,extra-,,air ,,valve 7,e74 ,the carburettor proper may be constructed in a variety of forms1 but the elements of which it is composed are3 7#a7 the float chamber ,a1 7#b7 the petrol jet ,b1 7#c7 the choke tube ,c1 7#d7 the mixing chamber ,d1 and 7#e7 the throttle valve ,e1 as shown in ,fig4 #ci4 ,illustration3 ,,fig4 #ci4--,,sectional ,,drawing ,,of ,a ,,carburettor ,,of ,,the ,,jet ,,type4 ,the ,float ,chamber is generally cylindrical in form and the liquid enters at the bottom1 the flow being regulated by a pointed rod called a needle valve4 ,a hollow metal float which can slide freely up and down the needle valve stem operates two levers which are pivoted on the float chamber cover4 ,it is well known that when a body is immersed in a liquid the liquid exerts an upward pressure on the body equal to the weight of liquid displaced by the body4 ,the float being hollow and made of very thin sheet metal1 displaces a very large quantity of liquid in proportion to its own weight1 and is therefore very buoyant4 ,the buoyancy of the float will1 of course1 depend on the density of the liquid in the float chamber1 and it will naturally sink deeper down into petrol than it would into a heavier spirit such as paraffin or benzol4 ,the action of the float is as follows3--,supposing the petrol to be turned off and the needle valve lifted up off its seating1 then on turning on the petrol supply the petrol will run into the float chamber1 and as the level of the liquid rises the float will rise too1 lifting up the outer ends of the levers and depressing the needle valve down on to its seating by means of the collar which is rigidly attached to the spindle of the needle valve4 ,if at any time the level of the liquid in the chamber falls1 the float will fall also1 thus allowing the outer ends of the levers to drop and raise up the needle valve from its seating2 this allows more petrol to enter the chamber and raises the float again1 thus keeping a constant level in the chamber4 ,the height of the orifice in the top of the petrol jet above the bottom of the float chamber determines the height at which we require the liquid to stand in the chamber4 ,as a general rule the level of the liquid in the float chamber should be slightly below the top of the jet orifice to prevent the liquid oozing over and causing flooding or continuous dripping of petrol from the jet1 even when the engine is not running4 ,the height of the collar on the needle valve spindle must be adjusted until the float closes the valve down on its seating when the liquid has risen to the desired height in the float chamber4 ,hence1 if a carburettor has been adjusted to work with petrol1 it will require to have some slight extra weight added to the float when working with heavier spirits to cause it to sink to the required depth in these denser spirits4 ,the ,petrol ,jet and ,choke ,tube4--,the petrol jet generally consists of a short tube of fine bore1 one end of which contains a very small orifice for the purpose of spraying the petrol into the choke tube4 ,when the engine is at rest it is easily seen that the pressure of the air in the choke tube is atmospheric1 and that the pressure above the liquid in the float chamber is also atmospheric1 but when the engine is running it draws air up the choke tube at a very high speed and thus causes a partial vacuum round the petrol jet1 and therefore the petrol spurts out of the jet under the pressure difference which then exists and issues in the form of a fine spray which is readily vaporized4 ,the choke tube is purposely made of rather small diameter1 in order to get a high air speed1 which results in a low pressure round the jet and ensures a good driving force to spray the petrol out of the jet4 ,the speed of the engine is controlled by the position of the throttle valve or disc ,e1 which regulates the amount of air flowing up the choke tube1 and therefore incidentally checks the quantity of petrol issuing from the jet by regulating the vacuum in the neighbourhood of the jet orifice4 ,at low engine speeds there is very little suction or vacuum effect on the jet1 but at high engine speeds with full throttle opening the maximum suction of the engine is exerted upon the jet4 ,thus at low speeds with this type of carburettor we do not get enough petrol out of the jet1 and at high speeds we get too much1 which results in too weak a mixture at low speeds and too rich a mixture at high speeds4 ,one reason for this is that the air flows out of the choke tube faster than it flows into it1 owing to the fact that its volume increases as the pressure decreases1 and hence the pressure round the jet falls very rapidly indeed as the air velocity increases and causes too much petrol to issue from the jet in proportion to the quantity of air flowing through the tube4 ,the choke tube is often a plain piece of pipe1 as shown in ,fig4 #dj1 instead of being tapered as in ,fig4 #ci4 ,the ,mixing ,chamber and ,throttle ,valve4--,the throttle valve is usually a plain flat disc of metal mounted on a spindle which can be rotated and thus regulate the size of the air passage to the engine4 ,it is placed above the petrol jet and situated in the mixing chamber1 which is simply a short length of pipe 7of the same bore as the engine induction pipe7 surrounded by a hot-water jacket1 the supply of hot water being drawn from the engine cooling system4 ,the heat from this jacket should be sufficient to make up for the fall in temperature that would otherwise result due to the vaporization of the petrol as explained above4 ,illustration3 ,,fig4 #dj4--,,plain ,,form ,,of ,,choke ,,tube4 ,recent ,improvements in ,carburettors4--,another defect of this simple type of carburettor becomes apparent in the larger sizes required for multi-cylinder engines4 ,to pass the requisite quantity of petrol to keep the engine running at high speeds without creating too great a suction effort and thereby hampering the engine1 necessitates the use of a jet of larger calibre1 so that the liquid is no longer sprayed but issues in the form of a fine stream which is not readily vaporized4 ,this has been overcome by the use of multiple-jet carburettors which have several jets each surrounded by its own choke tube1 but all controlled by one throttle valve and supplied from one common float chamber4 ,in this case the total cross-sectional area of all the jet orifices together could be made sufficient to pass the necessary quantity of fuel1 but the bore of each individual jet orifice would be comparatively small and spraying would result as before4 ,another very successful device is shown in ,fig4 #da1 in which ,a is the petrol jet which1 in this case1 has no special orifice and is surrounded by a larger tube ,b containing small holes for the inlet of air and outflow of petrol4 ,as the petrol issues from the jet it strikes against the pointed cone on the end of the screw ,c1 and is thus very successfully atomized and broken into small particles which can be readily vaporized4 ,illustration3 ,,fig4 #da4--,,petrol ,,jet1 ,,specially ,,arranged ,,for ,,atomising ,,the ,,petrol4 ,illustration3 ,,fig4 #db4--;,,compensated ,,petrol ,,jet4 ,a ,,is ,,the ,,main ,,jet ,,and ,b ,,the ,,compensating ,,jet ,,supplied ,,through ,,the ,,orifice ,c4 ,there are several devices for keeping the strength of the mixture constant at all engine speeds irrespective of the amount of vacuum in the choke tube4 ,one of the best of these is illustrated in ,fig4 #db1 and consists in the use of a compensating jet4 ,the main petrol jet ,a is of sufficient size to supply the requirements of the engine under full speed and with the resulting high vacuum2 it is fed directly from the float chamber in the usual manner4 ,the compensating jet ,b surrounds the main jet and is supplied with petrol through an orifice ,c1 so arranged that it offers a greater resistance to flow than the passage up the centre of the main jet4 ,at all engine speeds up to a certain predetermined maximum the compensating jet will supply most of the petrol1 but as the demand increases the main jet will also begin to supply1 and simultaneously the compensating jet will commence to go out of action owing to its supply of petrol becoming partly or wholly exhausted due to the restriction of the orifice ,c4 ,the simple jet-in-tube carburettor has been greatly improved by the addition of an automatic extra-air valve1 of which a simple form is shown in ,figs4 #dc and #dd4 ,it consists of a small mushroom type valve ,a1 with its seating ,b so arranged that it can be screwed into the induction pipe of the engine4 ,the valve is held up against its seating by a light spring ,c1 so that at high engine speeds when there is a good vacuum in the induction pipe the pressure of the atmosphere will open the valve against the tension of the spring and allow air to pass into the induction pipe1 thus reducing the amount of vacuum and simultaneously weakening the mixture4 ,illustration3 ,,fig4 #dc4--;,,automatic ,,spring ,,controlled ,,extra-,,air ,,valve4 ,illustration3 ,,fig4 #dd4--,,plan ,,view ,,of ,,automatic ,,extra-,,air ,,valve4 ,the points of a good carburettor3-- ,these may be set out in the following order-- 7#a7 ,complete atomization and vaporization of the liquid fuel at all engine speeds4 7#b7 ,the supply of an adequate quantity of gas of the correct proportions with all throttle openings and at all temperatures4 7#c7 ,sufficient mechanical strength and durability to withstand road shocks and to ensure freedom from breakdowns without undue weight or complications4 7#d7 ,ability to continue working correctly when the car is on an incline or affected by the camber of the highway4 7#e7 ,moderate first cost4 ,pressure ,feed and ,gravity ,feed4--,in ,fig4 #ch we showed a gravity-fed system or one in which the petrol is fed from the tank to the float chamber of the carburettor by the action of gravity only4 ,for this system to be successful at all times the carburettor must be placed low down to obtain a good head for the flow of petrol in the connecting pipes1 as there is a practical limit to the height at which the petrol tank can be fixed4 ,also the pipes must have a continuous run down towards the float chamber to prevent air-locks in them1 and they must be kept away from the hot exhaust system4 ,when all these points can be secured this system is perfect4 ,an alternative system is to force the petrol into the float chamber by maintaining an air pressure 7of #b or #c lb4 per square inch7 on the surface of the liquid in the petrol tank4 ,with this arrangement the carburettor may1 if desired1 be situated above the level of the petrol tank in a more accessible position1 but it necessitates the fitting of a small air pump on the engine and the use of a hand air pump for starting4 ,,chapter ,,vi ,,ignition ,,and ,,ignition ,,devices ,we have already stated that the charge of explosive mixture is ignited in the cylinder at the end of the compression stroke by means of an electric spark4 ,the electric spark takes place as the result of an electric discharge across the gap between the electrodes of the sparking plug4 ,illustration3 ,,fig4 #de4--,,sectional ,,drawing ,,of ,a ,,sparking ,,plug4 ,the ,sparking ,plug4--,two views of a typical sparking plug are shown in ,figs4 #de and #df1 in which ,a is the high tension electrode which is periodically charged with electricity at high voltage 7or electrical pressure7 from a high tension magneto or a high tension coil1 and ,b#a1 ,b#b are electrodes which1 being in metallic contact with the cylinders and framework of the engine1 are thus at zero potential4 ,the electric discharge occurs across the gap ,c#a1 ,c#b in the form of a spark or flash4 ,the electrode ,a is heavily insulated from the metal casing ,d of the sparking plug by porcelain insulators ,e and ,f4 ,the locknuts ,g and ,h serve to keep the plug gas-tight and hold the several portions together mechanically4 ,the terminal ,k is used for clamping the wire 7or lead7 which brings the supply of high tension electricity4 ,the high tension electric current may be supplied either by 7#a7 a magneto machine or 7#b71 a coil and accumulator ignition system4 ,illustration3 ,,fig4 #df4--;,a ,,sparking ,,plug4 ,illustration3 ,,fig4 #dg4--,,outside ,,view ,,of ,a ,,high ,,tension ,,magneto4 ,illustration3 ,,fig4 #dh4--;,,end ,,view ,,of ,a ,,high ,,tension ,,magneto1 ,,showing ,,high ,,tension ,,distributor ,,and ,,low ,,tension ,,contact ,,breaker4 ,the ,high ,tension ,magneto4--,in ,figs4 #dg1 #dh and #di we show a modern high tension magneto suitable for a four-cylinder engine4 ,it consists of the stationary magnets ,a1 the driving spindle ,b1 the high tension electrode ,d1 the high tension distributor ,c1 and the low tension contact breaker ,e4 ,the armature1 condenser1 and distributor gear wheels are not shown in the drawings1 but are situated inside the machine in the space between the high tension electrode ,d and the low tension contact breaker ,e4 ,as the spindle ,b is rotated by gearing driven from the engine crankshaft the armature attached to it generates a high tension current and a low tension current4 ,the high tension current passes to the high tension electrode ,d and thence across the machine to the carbon brush ,h of the high tension distributor ,c4 ,the low tension current passes through the platinum-tipped contact screws ,f#a1 ,f#b of the low tension contact breaker4 ,twice during each revolution of the armature these contacts are separated owing to the fibre block attached to the bell crank lever ,g passing over the stationary cams ,t#a1 ,t#b2 this constitutes the make-and-break device for interrupting the primary current4 ,the momentary interruption of the primary current in this way causes a very great increase in the electrical pressure 7or voltage7 of the secondary or high tension current which is sufficient to bring about the spark discharge across the gap between the electrodes of the sparking plug4 ,since there are two of these cams on the low tension contact breaker it will be understood that the armature can supply current for two sparks in every revolution it makes4 ,if we bear this fact in mind we will have no difficulty in determining the relative speeds of the magneto armature and the engine crankshaft for any type of engine4 ,a four-stroke engine requires one spark in every two revolutions made by the crankshaft1 so that a four-cylinder engine of this type requires two sparks per revolution1 and the magneto armature must run at crankshaft speed4 ,a six-cylinder engine working on the four-stroke cycle would require three sparks per revolution1 but the armature of the magneto only supplies two1 therefore it must be driven at one-and-a-half times the crankshaft speed4 ,illustration3 ,,fig4 #di4--;,,end ,,view ,,of ,a ,,high ,,tension ,,magneto1 ,,showing ,,the ,,earthing ,,terminal 7,p74 ,the high tension distributor consists of the carbon brush ,h driven by gearing from the magneto armature and the metal segments ,m#a1 ,m#b1 ,m#c1 ,m#d1 which are mounted in a block of insulating fibre4 ,there must be as many segments on the distributor as there are cylinders on the engine1 one segment for each sparking plug2 but the armature cannot supply more than two sparks per revolution1 and therefore if the distributor has four segments it must be driven at half the armature speed1 and if it has six segments it must be driven at one-third of the armature speed4 ,each metal segment is electrically connected to a sparking plug lead such as ,l#a1 ,l#b1 ,l#c1 ,l#d4 ,the high tension electrode ,d is attached to a light carbon brush which presses on a gunmetal collector ring at the high tension end of the armature winding4 ,a special terminal is provided at ,p1 so that when a wire is attached to it and connected to the frame of the engine 7usually through a switch7 the low tension windings are short-circuited or closed on themselves1 and the make-and-break has no effect1 because there is always the path through the switch until it is opened again4 ,under these circumstances the voltage of the high tension circuit is not sufficient to cause the spark discharge1 and the ignition is then said to be switched off4 ,the instant at which the spark occurs may be advanced or made earlier by moving the rocker arm ,k1 which carries the stationary cams ,t#a1 ,t#b backwards1 whereas if it is moved forward the ignition is retarded and occurs later in the stroke4 ,normal ignition occurs when the lever is midway in its range of movement and corresponds to the position of the piston when the crank is on the top dead-centre1 whereas advanced ignition occurs just before the piston has completed the compression stroke1 and retarded ignition will take place after the crank has passed the dead-centre and when the piston has moved down a little on the power 7or explosion7 stroke4 ,advancing the ignition increases the speed1 and retarding the ignition reduces the speed1 except when the engine is overloaded1 and then it may pick up speed a little or run better if the ignition is slightly retarded--but the exact behaviour will depend on the temperature of the metal walls and piston within the cylinder4 ,illustration3 ,,fig4 #ej4--;,,an ,,ignition ,,coil1 ,,showing ,,the ,,trembler ,,mechanism4 ,we have mentioned that normal ignition occurs when the crank is exactly on the dead-centre and the piston at the top of its stroke4 ,if we set the magneto when the engine is at rest so that ignition ought to occur on dead-centre when the arm ,k is in its mid position the actual sparking will be late on account of the time lag of the electric current4 ,the current takes time to flow and in that brief element of time the crank has moved a few degrees off the dead-centre1 at high speeds4 ,hence the ignition must be advanced if the charge is to be correctly fired when the engine is running fast4 ,if the ignition is too far advanced it will cause the engine to 8knock10 especially under heavy loads4 ,if the ignition is retarded the charge is not fired at the commencement of the stroke so that a portion of the power theoretically available in the fuel is lost to exhaust at the end of the stroke4 ,retarded ignition always causes overheating of the exhaust system4 ,if the arm ,k is fixed mechanically in its mid position so that the ignition can neither be advanced nor retarded1 we have what is known as fixed ignition4 ,illustration3 ,,fig4 #ea4--;,,ignition ,,coil ,,case4 ,illustration3 ,,fig4 #eb4--,,low ,,tension ,,contact ,,breaker ,,for ,,single ,,cylinder ,,coil ,,ignition ,,system 7,,wipe ,,contact74 ,an ,ignition ,coil suitable for a single cylinder engine is shown in ,figs4 #ej and #ea1 in which ,a and ,b are the low tension terminals and ,c is the high tension terminal4 ,the trembler blade is shown at ,d1 with the adjusting screw ,f and the platinum-tipped contacts ,g#a1 ,g#b4 ,the iron core of the coil projects a little above the case1 as shown at ,e in ,fig4 #ej4 ,the strength and character of the spark may be varied considerably by slightly screwing ,f up or down4 ,when current is supplied to the low tension terminals of the coil it flows through the primary winding and magnetizes the iron core1 completing its circuit by passing across the platinum contacts4 ,when the trembler blade is attracted to the iron core the primary circuit is broken by the temporary separation of the platinum contacts1 and therefore the magnetism ceases1 the trembler is released1 and the circuit is completed again4 ,thus the trembler blade is set rapidly vibrating and making and breaking the primary circuit as long as the roller attached to the rotating arm ,h of the low tension contact breaker shown in ,fig4 #eb is in contact with the metal segment ,k1 and this results in the production of a succession of sparks at the sparking plug which is connected to the terminal ,c of the high tension winding4 ,this is very useful especially when starting an engine1 but with modern high-speed engines the trembler has only time to give one spark at high engine speeds1 and therefore the magneto has the advantage except for easy starting4 ,this has led to the introduction of dual ignition systems1 and in particular to that system in which the main ignition is by magneto1 but there is a supplementary coil fitted to supply high tension current to the ordinary high tension magneto distributor when the engine is at rest1 the coil being cut out after the engine has got up speed4 ,but this has been largely superseded by the use of electric motors for starting the engine1 although the magneto is still relied upon for the ignition of the charge in the cylinders4 ,the contact breaker and coil just described would be very suitable for a single cylinder petrol engine1 or a non-trembler coil might be used in conjunction with a contact breaker of the quick break type used on magnetos and illustrated in ,fig4 #dh4 ,in the case of a multi-cylinder engine having coil ignition we may use separate coils without a high tension distributor1 or a single coil and a high tension distributor having as many segments as there are engine cylinders and arranged similarly to the magneto distributor of ,fig4 #dh4 ,when no high tension distributor is fitted there must be a separate coil for each cylinder1 and the high tension wire runs direct from the coil to the sparking plug1 so that the character of the spark as well as the exact instant at which it occurs may not be the same in each of the cylinders4 ,if there is a high tension distributor it should be mounted on the same driving spindle as the low tension contact breaker1 in order that the ignition may be synchronized1 i4e41 the spark will occur at the same point in the piston's stroke for all the cylinders4 ,the ignition may be advanced or retarded by moving the casing of the low tension contact breaker relative to the roller arm1 thus causing it to make contact either earlier or later in the revolution4 ,at one time it was thought that two-point ignition gave increased power and efficiency4 ,two-point ignition means simultaneous firing of the charge from more than one plug4 ,sometimes two high tension leads were led from each distributor segment and connected to the two plugs in the corresponding cylinder--this constituted the parallel system4 ,another system employed a special plug with both electrodes insulated from the engine frame2 this was coupled in series with an ordinary plug so that the spark jumped the gaps in succession4 ,it is quite evident1 however1 that if the gas is thoroughly mixed up and in a state of violent agitation as the result of rapid compression1 a single well-placed spark will fire it successfully and so no gain results from simultaneous ignition at another and less favoured point4 ,illustration3 ,,fig4 #ec4--,,wiring ,,diagram ,,for ,,four ,,cylinder ,,engine ,,with ,,high ,,tension ,,magneto ,,ignition4 ,wiring ,diagram for ,magneto ,ignition ,system4--,the electrical connexions are extremely simple in the case of a high tension magneto ignition system4 ,in ,fig4 #ec we show a four-cylinder engine fitted with high tension magneto4 ,the only wires required are the four high tension cables from the high tension distributor to the sparking plugs and the earthing wire leading from the short circuiting terminal to the frame of the engine through a switch as indicated4 ,the firing order of the cylinders may be either #a1 #c1 #d1 #b or #a1 #b1 #d1 #c1 as desired 7provided the cranks are arranged in the usual manner1 that is1 in the order shown in ,fig4 #ba74 ,in determining the order of firing of the respective cylinders the engine should be turned round very slowly by hand and careful note made of the order in which the firing strokes occur4 ,to determine the firing stroke the piston should be moving downwards and the position of the valves noted2 if both valves are shut then this is the firing stroke1 but if the inlet valve is opening it is the suction stroke4 ,wiring ,diagram for a ,coil ,ignition ,system4--,the electrical connexions for a coil ignition system are slightly more difficult to follow out2 they are shown in ,fig4 #ed for the same engine illustrated in ,fig4 #ec4 ,in the diagram we show four separate trembler pattern coils1 each of which can give a succession of sparks as long as contact is being made on any one segment of the low tension contact breaker connected to it4 ,all the low tension terminals of the coils are connected together to a common busbar1 which is supplied with current from the accumulator direct4 ,the current flows from the busbar through the low tension windings of each of the coils in turn1 as it comes into operation through the engine-driven contact breaker1 and returns to the battery through the frame of the engine4 ,high tension cables lead from the high tension terminal of each coil direct to the sparking plugs1 and therefore the ignition is not necessarily synchronized4 ,illustration3 ,,fig4 #ed4--,,wiring ,,diagram ,,for ,,four ,,cylinder ,,engine ,,with ,,trembler ,,coil ,,ignition4 ,when the switch in the low tension circuit is opened the ignition is off1 because the current is then permanently interrupted2 when the switch is closed the ignition is on4 ,to economize current a quick make-and-break device should be used instead of the wipe form of contact breaker illustrated1 and a non-trembler coil used4 ,it is very important to fully retard the ignition lever when starting an engine having coil ignition1 because it is very liable to backfire and injure the operator's wrist2 with magneto ignition this is less liable to happen4 ,timing the ,ignition4--,various instructions are given from time to time for correctly timing magneto ignition1 but the following will be found to give satisfactory results4 ,first ascertain the firing order of the cylinders as explained above1 and then bring ,no4 #a piston on to the top dead-centre4 ,rotate the driving spindle of the magneto until the carbon brush ,h of the high tension distributor makes contact on the segment connected to the lead marked 7#a74 ,if the leads are not marked it will be necessary to determine which is ,no4 #a by observing the direction of rotation of the brush4 ,next adjust the position of the driving spindle very carefully by turning it to and fro1 so that when the ignition lever ,k 7see ,fig4 #dh7 is in its mid position the platinum contacts ,fl1 ,f#b are fully separated1 the brush ,h still being on segment ,no4 #a4 ,then push the magneto gear wheel into mesh with the engine gear wheel which is to drive it1 and firmly bolt down the magneto to its bracket4 ,similar instructions may be followed out for the coil ignition system4 ,,chapter ,,vii ,,lubrication ,properties of ,oils4--,owing to the very high speed at which the modern petrol engine runs great attention must be paid to lubricating the moving parts1 otherwise undue wear or even seizure will result4 ,we must be very careful to choose a suitable oil1 one which is chemically pure and retains its lubricating properties at high temperatures4 ,a considerable amount of oil finds its way into the cylinder1 where it comes into direct contact with the hot gases4 ,if an oil is heated a temperature will sooner or later be attained1 when the oil will give off an inflammable vapour1 i4e41 one which will burn4 ,this temperature is called the flash point of the oil4 ,if the oil is likely to get into the cylinder of a petrol engine it should have a very high flash point2 in fact1 most of these oils do not flash until well over #djj ,fahrenheit4 ,also when the oil is burnt it must not leave any appreciable residue4 ,some oils are very defective in this respect1 and leave large quantities of carbon deposit on the metal walls of the cylinder and the valves2 others again are gummy or too viscous even at high temperatures4 ,such oils must be avoided equally with those which lose their viscosity too much under heat4 ,splash ,system of ,lubrication4--,one method of lubricating the working parts is known as the splash system4 ,in this system oil is poured into the crankchamber and the moving parts dip into it1 splashing it all over the interior of the crankcase and the lower portions of the cylinder walls4 ,oil holes are drilled in such positions that as the oil drops down again after being splashed upwards some of it will fall into these holes and lubricate the bearings4 ,this is a very cheap method of lubrication in first cost1 but very wasteful and unsatisfactory in regular use1 hence it has practically died out4 ,as the oil is used up a fresh supply must be admitted by some form of continuous drip-feed arrangement1 the oil being forced over very often from a small tank on the footboard by means of air pressure or the pressure of the exhaust gases from the engine4 ,it is very difficult under these circumstances to estimate how much oil is present in the crankchamber at any given instant1 so that there was usually alternately too much or too little4 ,too little oil meant undue wear on bearings 7perhaps seizure71 and too much oil meant a smoky exhaust which became very obnoxious when the engine was suddenly accelerated4 ,illustration3 ,,fig4 #ee4--;,,improved ,,system ,,of ,,splash ,,lubrication4 ,improved ,system of ,splash ,lubrication4--,this is a combination of the splash system and the forced system1 and is shown in ,figs4 #ee and #ef4 ,in these figures ,a#b and ,a#c represent two of the main engine bearings which support the crankshaft2 ,c#a1 ,c#b1 ,c#c are three of the crankpins2 ,f#a1 ,f#b1 ,f#c are oil troughs placed under the crankpins2 ,d#b1 ,d#c are oil feed pipes to the main bearings4 ,generally speaking1 the oil is drawn from the bottom of the crankcase by means of a pump1 and this pump delivers the oil to some form of indicator mounted on the dashboard of the car4 ,after passing through the indicator the oil flows by two main pipes1 one of which feeds the main bearings by means of branches ,d#b1 ,d#c1 etc41 and the other feeds oil troughs by means of branches such as ,g#b4 ,when the troughs are full the oil overflows into the bottom of the crankchamber1 and so there is always a constant depth of oil for the scoops attached to the connecting rod ends to dip into1 and one great drawback to the splash system is overcome2 also the main bearings are always sure of being amply supplied4 ,the oil pump may be an ordinary plunger type pump or a rotary pump4 ,illustration3 ,,fig4 #ef4--,,sectional ,,view ,,of ,,end ,,of ,,connecting ,,rod1 ,,showing ,,arrangement ,,of ,,scoop ,,and ,,oil ,,trough4 ,forced ,lubrication4--,one system of forced lubrication is shown in ,fig4 #eg4 ,the general arrangement of the system is very similar to the preceding one1 except that there are no troughs in the crankchamber and all the bearings receive an ample supply of oil under pressure so that the journals are supported in their bearings on a film of oil and the metals never come in direct contact with each other4 ,after entering the main bearings the oil passes through holes drilled in the crankshaft and thus positively lubricates the crankpin bearing1 passing up the connecting rod either internally as shown or by an external pipe it lubricates the gudgeon pin and then falls down into the crankchamber4 ,on its way down it gets splashed about and thus lubricates the cylinder walls and piston2 sometimes these are positively lubricated by leading the oil through the centre of the gudgeon pin direct to the surface of the cylinder walls--but this often gives an excess of oil and causes a smoky exhaust4 ,in ,figs4 #eh and #ei we show two views of a very popular form of oil pump for forced lubrication systems4 ,it consists of two gear wheels1 one of which is driven by a spindle from the engine crankshaft1 and it drives the second wheel by means of the projecting teeth4 ,the oil is picked up by the teeth and passed round from the suction to the delivery side of the pump on the outer edge of the wheels2 no liquid can pass direct across between the teeth which are in mesh1 and hence the direction of rotation is as shown by the arrows4 ,illustration3 ,,fig4 #eg4--;,,forced ,,lubrication ,,system4 ,illustration3 ,,fig4 #eh4 ,illustration3 ,,fig4 #ei4 ,,two ,,views ,,of ,a ,,rotary ,,oil ,,pump ,,for ,,forced ,,lubrication4 ,the difficulty of securing a really good lubricant for petrol engines must be apparent from a study of the prices of the various oils4 ,it will be observed that they are all considerably more expensive than petrol1 and therefore we must economize in their use4 ,the old splash system was very wasteful and consumed oil at the rate of one gallon every hundred miles at least1 but a modern system of forced lubrication will not require more than one gallon of oil every thousand miles4 ,perhaps an average everyday figure for ordinary motor-car engines would be one gallon every #bej miles4 ,the pressure of the oil in a forced feed system varies in different makes of engines from #e up to #dj pounds per square inch--a very common figure1 however1 is #aj pounds per square inch4 ,the speed of the oil pump also varies considerably1 and ranges from #ejj up to #b1jjj revolutions per minute at normal engine speed4 ,generally a small relief valve is fitted in the pump casing1 which returns oil to the crankchamber if the pressure tends to rise above the desired limit due to the engine speed increasing4 ,we have mentioned already that the flash point is generally over #djj ,fahrenheit when the oil is new1 but after it has been in the crankcase some time and got used over and over again it is found that the petrol vapour leaking past the piston rings of the engine condenses when the engine cools down after a run and drops into the oil in the sump1 thus lowering its viscosity and its flash point4 ,according to ,mr4 ,morcom it may come down as low as #bjj ,fahrenheit 7about71 but if the oil is heated and the petrol driven off the flash point goes up again4 ,therefore it is a good plan with forced lubrication systems to empty the old oil out periodically and fill up entirely with fresh oil4 ,,chapter ,,viii ,,cooling ,we have already explained the necessity for cooling the cylinders of a petrol engine by means of a water-jacket1 and we now proceed to show how the circulation system may be arranged4 ,there are two forms of circulation in use3 7#a7 ,natural2 7#b7 ,forced4 ,illustration3 ,,fig4 #fj4--,,thermo-,,syphon ,,water ,,cooling ,,system4 ,natural or ,thermo-,syphon ,circulation4--,this system is shown in ,fig4 #fj1 and may be explained as follows3--,the heat generated by the successive explosions within the cylinder causes the water at the top of the cylinder jacket ,a to get hot4 ,as a column of hot water is lighter than one of cold water of equal height1 the heated water rises up the pipe ,b and flows into the top of the radiator ,d1 while colder water from the bottom of the radiator flows up the pipe ,c and into the cylinder jacket ,a4 ,it is important that the height of the water in the radiator ,d should be at such a level that the outlet from the pipe ,b is submerged4 ,illustration3 ,,fig4 #fa4--;,,forced ,,water ,,circulation ,,by ,,means ,,of ,a ,,pump 7,p74 ,in the radiator the water falls through a series of tubes ,e1 having gills or fins on the outside for the purpose of dissipating the heat4 ,the cooling of the water is also assisted by the fan ,f1 which is driven from the fan pulley ,g and draws air past the radiator tubes at high speed4 ,sometimes the water in the radiator is made to fall through a series of cells which are formed of cast aluminium2 such a radiator is called a honeycomb radiator4 ,it is important that the pipe ,c should not have any sharp bends and it should not rise very much in height1 but the outlet pipe ,b may have a considerable rise with advantage4 ,both the inlet and outlet pipes should be of large diameter with this system of circulation1 and the radiator should be so arranged that there is a good head of water above the cylinders4 ,in the drawings ,h is the front cross-member of the chassis1 ,k is the starting-handle clutch1 and ,l is the starting handle4 ,forced or ,pump ,circulation4--,with this system the water is positively circulated through the jackets2 it is drawn from the bottom of the radiator by the pump ,p 7,fig4 #fa71 which is mechanically driven from the valve shaft of the engine1 and delivered under pressure to the jacket ,a4 ,the outlet of the pipe ,b need not be drowned1 and the pipe ,c may be arranged in any way most convenient to the chassis4 ,sometimes when a pump is fitted the pipes are arranged so that the system may be operated as a thermo-syphon in the event of a breakdown of the pump4 ,it is not uncommon to experience trouble due to leakage at the pump gland1 which results in gradual loss of water from the system1 and therefore the thermo-syphon or natural circulation has much to recommend it4 ,also it may be said that the pump represents an additional complication to the engine and means increased first cost4 ,every moving part we add to the engine is of course an additional potential source of trouble1 but the addition of a really first-class water circulating pump of the type shown in ,fig4 #eh cannot be said to be anything but a reasonable precaution4 ,the weight and size of every part of a motor-car engine and chassis have been so much reduced recently1 owing to competition with ,american firms1 that many manufacturers who adopted the thermo-syphon principle experienced great trouble with it owing to the small size of radiator fitted1 as well as faulty arrangement of the connexions4 ,considering any one engine1 it follows that if a certain size of radiator and a given quantity of water in the circulating system will keep the engine cool when a pump is used to give a positive circulation1 then a larger radiator and greater quantity of water will be required for natural circulation4 ,thermo-syphon circulation also means a high radiator and bonnet1 which many people object to on the score of appearance1 without considering its utility4 ,with natural circulation greater care must be exercised to keep the radiator well filled1 but this often leads to other difficulties on bad roads owing to the water splashing from the overflow pipe and finding its way on to ignition appliances4 ,before starting an engine it is always advisable to remove the radiator filling cap and examine the water level2 if it should happen that at any time while the engine is running the circulating system runs quite dry1 owing to a breakdown or leakage1 do not attempt to pour water into the radiator1 but simply raise both sides of the bonnet and leave the engine to cool down first4 ,again1 when filling the radiator for a forced circulating system1 it is desirable to give the engine a turn or two with the starting handle occasionally to operate the pump and prevent air locks2 very often the radiator appears to be full1 but as soon as the engine commences to run the water disappears owing to the system not being full1 due to the above-mentioned cause4 ,in cold or frosty weather all the water should be drained off from the circulating system when the car is in the garage1 unless the garage is heated or some anti-freezing solution is used4 ,glycerine or alcohol added to the water will prevent it freezing1 but as an additional precaution in cold countries one often sees travelling rugs strapped over the radiator and bonnet4 ,occasionally one gets trouble due to the water boiling in the jackets1 and on this account reasonable care should always be exercised in unscrewing the radiator filling cap if the presence of steam is suspected4 ,an engine may have been running well for a long time without trouble and then develop symptoms of overheating in the circulation system4 ,this overheating may be either local or general4 ,local overheating may result from some partial seizure of the piston in the cylinder due to dirt on the walls1 or from the presence of grease on the outside of the cylinder walls1 in the jacket space4 ,if grease is suspected or there is furring up in the passages of the jacket due to bad water supply1 the trouble may be cured by adding some common washing soda to the water in the radiator and running the engine with the car at standstill for half-an-hour or so4 ,after this drain off all the water and sludge1 allow the engine to cool down1 and then fill up again with clean water4 ,general overheating may result from leaky pistons and pistons rings1 or from the use of too weak a mixture in the carburettor1 or from overloading the engine4 ,if the mixture supplied to the engine is very weak1 the overheating will be very marked on the exhaust side of the engine4 ,local overheating causes the engine to 8knock0 badly4 ,in arranging the jackets and the pipes care must be taken to arrange that a cock is placed at the lowest point in the system1 so that the whole may be completely emptied1 and the inlet pipe to the jacket should enter at the very bottom of the jacket chamber for the same reason4 ,it may be thought that all that is necessary is to provide plenty of space in the jackets round the cylinders and plenty of water in the whole system1 but experience shows that it is very important not to make the jacket space too large1 so as to ensure positive circulation and avoid local circulation in any one portion of the jacket4 ,when cylinders are cast in pairs the back pair have a tendency to discharge their hot water into the front pair and so back to the inlet pipe again1 hence this should be guarded against in arranging the outlet pipes4 ,pipes suitable for use with multi-cylinder engines are shown in ,fig4 #fb1 in which 7a7 is an outlet pipe for a monobloc casting1 and 7b7 and 7c7 are inlet and outlet pipes respectively for engines having separate cylinders4 ,it is advisable to modify the diameter of the branches by the insertion of metal orifice plates at the flanges to ensure an equitable distribution of the water among the several cylinders4 ,illustration3 ,,fig4 #fb4--;,,forms ,,of ,,water ,,piping4 ,the weight of water carried in the circulation system for a fifteen horse-power engine would be about #cj lb4 with pump circulation1 whereas #fj lb4 would be required for thermo-syphon cooling4 ,it is not desirable to cool the engine too much4 ,the jacket water temperature may be allowed to reach #ahj ,fahrenheit at full load1 but if this is exceeded there is liability to boiling4 ,given two similar engines of equal power and equally loaded1 one of which was operated with a jacket temperature of #ajj ,fahrenheit and the other at #ahj ,fahrenheit1 the hotter engine would show a gain in economy of from five to ten per cent4 in fuel consumption4 ,in considering the type of radiator to adopt1 one would not recommend the honeycomb variety 7except for appearance7 owing to the difficulty of cleaning the passages after it has been in use some time2 and the gilled tube would be more efficient than the plain tube4 ,the amount of tube required depends of course on its diameter1 but a rough approximation would be twelve feet of gilled tube or eighteen feet of plain tube 7of half-inch diameter7 per brake horse-power4 ,,chapter ,,ix ,,the ,,points ,,of ,a ,,good ,,engine ,choosing the ,number of ,cylinders4--,it is a very difficult problem to select the best engine for a particular purpose1 as there are so many factors which influence one's choice4 ,a single cylinder engine would only be used for a motor-cycle or a small car of low power2 the vibration and noise resulting from the use of a single cylinder petrol engine of even six horse-power are most objectionable1 and difficulties of starting and risk of engine unexpectedly pulling up and stopping are greatly enhanced4 ,the two-cylinder engine offers better prospects1 and was for some time considered quite good enough for most purposes1 but owing to its comparatively bad balance and its low torque it has fallen into disfavour4 ,we have seen how the rotating parts of the engine can be balanced1 but we have not considered the reciprocating parts4 ,to understand this question of balancing we must talk about 8inertia forces40 ,all bodies possess inertia1 that is1 they resent changes in their state of rest or motion4 ,if a body is moving uniformly it tends to keep on doing so1 whereas if it is at rest it tends to remain so4 ,to start the body off from rest1 or to stop the body and bring it to rest1 requires a force to be exerted1 and this force may be called the inertia force4 ,when a petrol engine is running at high speed the piston has to be started and stopped at the top and bottom of its stroke every time the crankshaft revolves once1 and to do this very large forces are needed1 because it has to be done so quickly4 ,these inertia forces take the form of pushes or pulls on the shaft and framework of the engine1 and thus cause vibrations to be set up4 ,if the periodicity or frequency of these forced vibrations happens to coincide with the natural period of vibration of the shaft material the shaft will commence to whip1 and may possibly break under the excessive strain4 ,in a two-cylinder engine with cranks #ahj degrees apart 7or half a revolution7 one piston is moving upwards and the other piston is moving downwards1 both at very high speed2 and both have to be brought to rest when the cranks come on their respective dead-centres4 ,the piston which is moving up tends to lift the shaft up with it1 and the one which is moving down tends to pull the shaft down with it1 because the connecting rods check the progress of the pistons and bring them to rest at the top and bottom of their strokes4 ,if these two pulls acted in line with each other they would balance1 but the cylinders are usually mounted side by side1 and then the two pulls virtually act at the ends of a bar whose length is the longitudinal distance between the vertical centre lines of the two cylinders4 ,thus these two inertia forces tend to rotate the whole engine first in a clockwise direction and then in a counter-clockwise direction1 according to which piston is moving up or down4 ,the only way to balance these forces under these conditions is to extend the crankshaft longitudinally and place another pair of cylinders and cranks in line with the first1 but so arranged that the inertia forces tend to turn the engine in the opposite direction to the first pair4 ,this gives us the well known four-cylinder arrangement so much in evidence at the present time1 the arrangement of cranks being shown in ,fig4 #ba4 ,a six-cylinder engine gives perfect balance if all the parts are of equal weight1 and the cranks at #abj degrees to each other in opposed pairs4 ,again1 a single-cylinder engine gives one power stroke in every two revolutions of the shaft1 a two-cylinder gives a power stroke in every revolution1 a four-cylinder gives two power strokes1 and a six-cylinder gives three power strokes in every revolution of the shaft4 ,hence a six-cylinder engine is very flexible 7i4e41 can accommodate itself easily to varying loads71 is perfectly balanced1 and can be made both powerful and economical4 ,one objection to the use of engines with multiple cylinders 7exceeding1 say1 four in number7 is that the crankshaft is more liable to vibrate and cause very harsh running at high speeds on account of the fact that the periodicity of the power impulses imparted to the shaft approaches the natural period of vibration of the shaft4 ,this effect arises from torsional oscillations and is distinct from the periodicity due to inertia forces which acts in the vertical plane4 ,a four-cylinder engine is nearly as good as a six-cylinder of equal power1 and is of course much cheaper in first cost1 takes up less room1 and weighs less4 ,a good four-cylinder engine will often prove more economical in running costs than a six-cylinder1 as it will probably be running a greater length of time at or near its full output1 and the work done on the idle strokes of the cycle will be less owing to the smaller number of cylinders4 ,another feature to consider is the arrangement of the cylinder castings4 ,a monobloc casting 7cylinders all in one casting7 gives a very short engine and reduces the length of the crankshaft1 but in the event of one cylinder bore being damaged the advantage lies with the separate cylinder construction4 ,the ,question of the ,valves4--,the question as to which is the better engine1 the sleeve valve or the poppet valve1 cannot be said to have been definitely decided yet4 ,the great feature of the poppet valve used to be its very quick opening and closing1 but nowadays engines turn over so fast that very strong springs are needed to close the valves in a reasonable time4 ,one complete revolution of the engine means that the crank has turned through #cfj degrees1 and the inlet valve is open while the crank turns through #aij degrees 7on the average71 but during part of this time it is being lifted or opened1 and during an equal period it is being closed4 ,the question then is1 8,how long does it remain fully open80 ,the answer is--not more than ten degrees at the most6 ,to keep the inlet valve open longer than this would require excessively stiff springs and throw a great strain on the valve gear4 ,now this is where the sleeve valve managed to get a look in--as one might say4 ,with two sleeves moving in opposite directions1 or one sleeve receiving a special form of motion1 we can open and close the ports and keep them fully open for just as long period or even longer than the poppet valve4 ,if it were not for the fact that sleeve valves are heavy and not so easy to keep gas-tight as poppet valves1 it is perfectly obvious that the poppet valve would have disappeared or taken second place long before this4 ,another great advantage of the sleeve valve is that by making large ports we can easily secure larger valve openings than are possible1 for practical reasons1 with a poppet valve4 ,it is now claimed also that the interior of the cylinders keeps free from carbon deposit much longer with sleeve valves than with poppet valves1 this carbon deposit being due chiefly to the use of too rich a mixture which causes the combustion to be imperfect and results in the deposit of solid carbon on the walls and sides of the combustion chamber4 ,carbon deposit is also caused by using unsuitable lubricating oil1 but it principally arises from the use of too rich a mixture for the purposes of securing quick acceleration4 ,perfect combustion is only secured by the use of a relatively weak mixture1 which would prevent the maximum power being developed and give rather a feeble acceleration4 ,modern engines have to be very carefully designed to reduce this nuisance of the carbon deposit to a minimum1 and also with a view to its speedy and efficient removal when it does take place4 ,detachable cylinder heads have been introduced principally to allow of rapid removal of carbon deposit from pistons and valves and the combustion chamber4 ,if the carbon deposit is allowed to accumulate1 pinking or sharp knocking commences1 due to pre-ignition of the charge by red-hot particles of carbon4 ,this results in loss of power1 and is first noticed by inability to climb steep hills that were formerly negotiated with ease4 ,mention must also be made of the great claim for silence of running of sleeve valve engines1 and this is thoroughly justified with high-class engines of the sleeve valve type1 provided they are in the hands of skilled drivers4 ,in unskilled hands one finds that the poppet valve is safer1 and will stand more knocking about without much increase in noise resulting4 ,rotary valves have fallen into disuse on account of the difficulty of keeping them gas-tight4 ,there is nothing to choose between poppet and sleeve valves on the score of economy in running4 ,economy and ,durability4--,a good modern petrol engine of reasonable size--say over #c in4 bore--will give one brake horse-power for an hour from the consumption of two-thirds of a pint of petrol4 ,this means that an engine giving #ab horse-power on the brake would use a gallon of petrol every hour4 ,but economy in petrol consumption is not the only desirable feature of a petrol engine4 ,there must be economy in lubricating oil and in cost of replacements or repairs4 ,nowadays the tendency with high grade steel alloys and other modern metals of high strength and durability is to cut everything down to its minimum size with a view to reducing the cost of production4 ,this often leads to many serious troubles in running on the road4 ,in choosing an engine one should carefully examine such points as provision for wear and adjustment1 strength and rigidity1 and whether the engine impresses one with a sense of its durability and also its general accessibility4 ,,chapter ,x ,,two-,,stroke ,,engines ,in the two-stroke type of petrol engine the cycle of operations is completed in two working strokes of the piston instead of the four required by the 8,otto0 cycle2 there is thus one explosion or power stroke in every revolution of the crankshaft4 ,theoretically this represents a great advance over the 8,otto0 cycle1 but difficulties and complications arise in the practical carrying out of the cycle4 ,the cycle on which it is desired to operate the engine is3 #ast stroke--,compression2 #bnd stroke--,explosion4 ,the charge would be introduced on the compression stroke and exhausted towards the end of the explosion stroke4 ,now the charge of gas required by the engine consists of a mixture of petrol vapour and air1 and it must either be sucked in or pushed in under pressure4 ,in the 8,otto0 cycle the charge is sucked in1 and in the two-stroke cycle it is delivered to the cylinder under pressure2 hence in the two-stroke cycle some form of pump is required which will suck in the charge of air and gas1 compress it a small amount1 and deliver it to the working cylinder at a pressure of #e or #f lb4 per square inch above atmospheric pressure4 ,this is where the complications commence2 if we fit a separate pump for each cylinder1 which is what would generally be done1 or if we made one pump serve for two cylinders1 we have to provide pump cylinders1 pistons1 rods and valves1 and therefore there is practically no gain over the four-stroke engine4 ,hence it is that inventors all try to avoid the use of a separate charging pump and turn their attention to the production of an engine in which one or more of the existing portions is made to serve as a pump for charging the working cylinder or cylinders with gas4 ,a favourite and fairly successful device is to make the crankchamber gas-tight and use it as the cylinder of the pump1 the underside of the engine piston then forming the pump piston which draws the charge from the carburettor into the crankchamber on its upstroke and compresses it on its downstroke1 delivering it to the working cylinder through the inlet port as soon as the piston has uncovered it by its downward movement4 ,,fig4 #fc4--,,two ,,port ,,type ,,of ,,two-,,stroke ,,engine ,,with ,,crankcase ,,compression4 ,there is no exhaust valve1 as the piston uncovers the exhaust ports a little before the inlet ports are opened4 ,to prevent the new charge escaping directly across the top of the piston from the inlet ports to the exhaust ports1 a deflector is fitted on the top of the piston equal in height to the height of the exhaust opening and situated immediately in front of and facing the inlet ports4 ,a two-stroke engine of the type referred to is shown diagrammatically in ,fig4 #fc4 ,e is the gas-tight crankchamber1 upon which the water-cooled cylinder ,a is mounted in the usual manner and fixed by studs or bolts4 ,the piston ,p carries the deflector ,h1 which is equal in height to the height of the exhaust opening ,g4 ,the piston rings are prevented from turning by pins so arranged that the joint of the rings does not pass across the ports4 ,the connecting rod ,d is of usual form1 and also the crankshaft ,c4 ,the carburettor1 or induction pipe leading from the carburettor1 would be attached to the flange ,l1 and the automatic valve ,f controls the admission of gaseous mixture from the carburettor to the crankchamber4 ,the inlet ports ,n are often only half the height of the exhaust ports4 ,on the upstroke of the piston a partial vacuum will be formed in the air-tight crankchamber1 which will allow the atmospheric pressure to force open the valve ,f against the pressure of the spring and enable the air to flow into the crankchamber through the carburettor and induction pipe1 carrying the charge of petrol vapour with it4 ,we must note1 however1 that no vacuum can be formed until the port ,n has been covered up by the piston1 so that a portion of the stroke is idle4 ,on the downward stroke of the piston the charge in the crankchamber is compressed1 and as soon as the piston uncovers the ports ,n the charge from the crankchamber flows up into the working cylinder1 displacing the burnt gases as it comes into the cylinder4 ,exactly what happens next it is difficult to say2 the probability is that this new charge rises in the cylinder a short distance 7but not a sufficient amount to displace all the dead gases from the top end of the cylinder7 and that some of it gets squeezed out of the exhaust opening as the piston rises and before it has had time to cover the exhaust ports4 ,thus1 owing to the idle portion of the stroke during admission to the crankchamber and to the low compression pressure adopted in the crankchamber1 the pumping portion of the engine has what is termed a very low volumetric efficiency4 ,it can be proved that this type of engine which endeavours to draw sufficient gas to fill its working cylinder into the crankchamber by means of a piston having only the same diameter as the diameter of the working cylinder itself1 and which cannot avoid some idle movement during the operation together with further loss from the exhaust opening1 is incapable of retaining more than a little over one-half a cylinder full of fresh combustible gas at the instant when compression commences2 the remainder of the contents must be dead exhaust gas4 ,thus1 even allowing for the double number of power impulses resulting from the use of the two-stroke cycle1 it is difficult to see how this form of engine could ever give more than about one and a quarter times the power of a four-stroke engine having the same bore and stroke even when the many difficulties experienced in the practical working of two-stroke engines have been overcome4 ,to use a high compression pressure in the crankchamber would increase the volumetric efficiency1 but would result in lost work during the pumping process1 besides being undesirable at the delivery stage of the process2 it is much better for the transfer of the gases to take place as gently as possible4 ,if too high a delivery pressure is used the fresh gas will enter in a sharp gust and get badly contaminated by mixture with the foul exhaust products instead of gently displacing them in bulk4 ,the use of an automatic valve is very desirable for the gas inlet to the crankchamber1 but unfortunately it limits the speed of the engine and also its flexibility or ability to pull well at all speeds4 ,an engine with an automatic valve runs best at that speed for which the tension of the spring is most suitable4 ,if the spring is weak the speed will be low4 ,tightening the tension on the spring will allow the engine to speed up1 but will prevent it running well at low speeds4 ,at high speeds and with correspondingly high tension the valve does not give enough opening1 and therefore limits the power of the engine4 ,it will1 therefore1 readily be seen that when a two-stroke engine with automatic inlet valves is pitted against a four-stroke engine with mechanically-operated inlet valves1 the comparison is unfair to the two-stroke cycle4 ,with the position and arrangement of ports shown in the drawings1 one must have a deflector on the piston head to prevent excessive loss of fresh gas through the exhaust opening4 ,after the engine has been running for some time at a high speed this deflector becomes very hot1 and as a general rule the cooling effect of the incoming gases is not sufficient to prevent it attaining a red heat on the compression stroke1 thus igniting the charge before the piston reaches the top of the stroke4 ,this defect1 which is called pre-ignition1 causes the engine to knock1 and results in a loss of power2 it may be partly overcome by admitting lubricating oil with the charge1 the oil then serving to cool the deflector as the charge enters the cylinder4 ,at high engine speeds there is great risk of the hot exhaust gases in the working cylinder setting fire to the incoming charge in the inlet ports1 thus causing backfiring into the crankchamber4 ,to avoid all possibility of backfire1 some form of air scavenging must be adopted1 but the general arrangement of this form of two-stroke engine does not lend itself to such an addition--it would merely reduce still further the quantity of gas reaching the cylinder4 ,a difficulty that is peculiar to multi-cylinder engines of the two-stroke type arises from the use of open exhaust ports4 ,the several cylinders generally discharge their exhaust gases into a common exhaust pipe or box1 so that if one cylinder happens to be missing fire the exhaust from another cylinder may set fire to the wasted charge--this is usually referred to as flashing-back from the exhaust and results in irregular and spasmodic knocking4 ,it will be clear from the foregoing that this cycle of operations1 which is so attractive from the theoretical point of view1 is not by any means so encouraging from the practical standpoint1 as many inventors have discovered4 ,the difficulties and failures of the early inventors which were so discouraging for them have only encouraged their successors and spurred them on to further efforts4 ,after a time the attempt to produce a simple two-stroke engine was abandoned generally1 and inventors turned their attention to improved forms of two-stroke engines1 some of which were very costly and complicated1 and none of which have survived for motor-car purposes4 ,the writer of this volume became interested in the problem of the two-stroke in connexion with one of these inventions for an improved engine1 and at a later stage patented and designed an improved engine of the two-stroke air scavenging variety1 which by that time had become a recognized type of two-stroke engine4 ,this engine was constructed and exhibited at one of the motor shows held in ,london some years ago4 ,a vast amount of experimental and research work was carried out on it by the writer1 but the work had to be abandoned when incomplete owing to the ,syndicate which financed the venture having exhausted its resources4 ,the promoters of the ,syndicate were anxious to produce an engine that would give double the power of a four-stroke engine1 but their early attempts were not at all successful4 ,one of their four-cylinder engines1 which would have been rated at #ce horse-power on the four-stroke cycle1 only gave #ab brake horse-power when tested by the writer4 ,the engine designed by the writer1 which we may call the ,kean two-stroke engine1 would have been rated at #be horse-power on the four-stroke cycle1 and gave approximately #ce brake horse-power4 ,although this result was excellent1 so much advance had been made in the four-stroke engine that it did not quite come up to the best results obtained on that system1 and hence we were unable to show any marked advantage to be gained from its adoption4 ,my experiments clearly pointed out the road to further success1 but owing to the partial failure of my attempt to beat the four-stroke engine we could not influence sufficient capital to reorganize and reconstruct the ,syndicate4 ,my engine had not been designed to secure a high speed of rotation but rather for strength and durability1 but it exceeded my expectations by turning up to #a1ejj revolutions per minute4 ,the four-stroke had1 however1 got well ahead of me by that time1 and #b1jjj was becoming common for it1 hence ,i was heavily handicapped in the race for horse-power4 ,illustration3 ,,fig4 #fd4--;,,diagrammatic ,,sketch ,,showing ,,how ,,the ,,duplex ,,type ,,of ,,two-,,stroke ,,engine ,,operates ,,with ,,air ,,scavenging4 ,a description of my engine will probably prove of interest4 ,to understand the principle of the engine we must turn to the diagrammatic sectional view of ,fig4 #fd4 ,instead of using the crankchamber of the engine as a gas pump1 this type of engine has a duplex piston1 and the pump chamber is formed by an annular extension of the main engine cylinder4 ,at first sight one would say this resulted in a very high engine1 but as a matter of fact the increase in height is not more than about #be per cent4 in the cylinders1 and there is no difference in the crankchamber height to that of a four-stroke engine4 ,the outstanding feature of the invention is the provision of a pump piston of larger effective diameter than the main piston and the arrangement of transfer pipes by which one pump feeds its neighbour's power cylinder1 and vice versa4 ,these are the basis of the invention1 and were being used a long time before the writer had even heard of this type of engine1 but it was left for him to seize upon their capabilities and correctly proportion the area of the annulus with respect to the main engine piston4 ,a careful study of the two-stroke problem revealed the inherent defect of the low volumetric efficiency and the tremendous possibilities of having an unlimited volume for the pump chamber by simply increasing the area of the lower or annular piston4 ,then followed the writer's attempt to tackle the outstanding practical difficulties enumerated above4 ,the engines already employed air scavenging1 but could not really use it effectively until proper proportions had been fixed upon for the respective pipes1 valves1 and ports4 ,the cycle of operations is as follows3--,on the downstroke of ,no4 #a piston the annular portion draws a charge of gas from the carburettor into the annular chamber ,d#a 7,fig4 #fd7 through the inlet valve ,b#a and at the same time pure air is drawn into the transfer pipe by the valve ,a#b4 ,on the upstroke the charges of air and gas are compressed into the transfer pipe1 and as soon as the piston ,p#b uncovers the inlet ports the air and gas enter the working cylinder4 ,in my engine ,i used a relatively high compression pressure for the transfer of the charge and curved the inlet ports up towards the head of the cylinder as shown4 ,the head of cylinder ,i made curved1 and the exhaust ports were carefully rounded and curved also4 ,the deflector on the head of the piston ,i inclined1 to curl the gases back against the wall of the cylinder1 and ,i reduced the height of the deflector to that of the inlet port 7instead of the exhaust port74 ,my ultimate aim was to abolish the deflector entirely by suitably shaping the inlet ports1 and ,i estimated that the path of the gases would be in the direction of the arrows4 ,the object of raising the compression pressure in the lower cylinder was twofold4 ,first of all ,i aimed at an increase of volumetric efficiency there1 and secondly ,i hoped to propel the scavenging air and the new charge right up to the head of the cylinder and so clear out all the dead gases4 ,then by suitably curving the head of the cylinder ,i expected to compel the scavenging air to keep going ahead of the gaseous mixture and curl round and down1 then following the exhaust gases out of the exhaust port4 ,my efforts in this direction were very unfortunately frustrated to a large extent by the fact that the cylinders of my engine had already been cast before ,i fully realized the tremendous importance of curving the cylinder head and giving a very steep inclination to the inlet ports4 ,we did our best to rectify matters in the machining and finishing stages1 but any engineer will understand the limitations now imposed upon us4 ,it was impossible to get new cylinders cast owing to lack of time and funds1 as we were intending to exhibit the completed engine4 ,thus ,i cannot say that my ideas were ever given a really satisfactory test2 the inlet ports were curved and inclined and the cylinder head was rounded off1 but not to such an extent that ,i can feel certain no further improvement could ever be made in those directions4 ,other improvements which ,i introduced were an improved automatic inlet valve for the gases1 which was fitted inside the induction pipe and whose spring tension could be adjusted while the engine was running without letting any air leak into the induction pipe2 also an improved air scavenging valve1 which could be set to give the full amount of air to the engine and yet be controlled from the dashboard of the car to give any desired quantity of scavenging air from no air up to full air4 ,very large inlet valves were fitted1 but when indicator diagrams were eventually obtained from the engine they showed that they were not nearly large enough and that the carburettor opening was too restricted1 thus cutting down the power 7and very likely the speed7 of the engine by probably over #be per cent4 ,high tension magneto ignition was fitted and thermo-syphon cooling4 ,arrangements were made to carry #hj lb4 of water in the system1 so that the engine never showed any tendency to boil even when the car had been running for long periods on the low gear4 ,a pump was afterwards fitted1 but it did not effect the cooling of the water any better than the natural circulation1 which was quite satisfactory4 ,the range of speed was from #aej revolutions per minute up to #a1ejj revolutions per minute2 the lower figure is very good indeed1 and can be attributed to the large number of impulses obtained due to the two-stroke cycle4 ,at the highest speed the crankshaft received #f1jjj impulses per minute1 or equivalent to a four-stroke engine running at #c1jjj revolutions per minute4 ,the effective pressure in the cylinder was1 however1 only just over #dj pounds per square inch1 due to the throttling at inlet already explained4 ,in a four-stroke engine we would expect just double that figure4 ,the extraordinary thing about this was that1 under heavy load1 when the speed was brought down to about #cjj revolutions per minute1 the effective pressure had risen to nearly #bjj lb4 per square inch1 but this appears to be due to imperfect scavenging 7or cleansing7 of the cylinder under these conditions4 ,the question of silencing the exhaust from the engine had caused me some difficulty in the earlier experiments1 so that ,i now tackled this problem and designed a special form of silencer in which the gases were first expanded to remove their pressure and then afterwards their velocity was taken up without shock4 ,this answered so well that a cut-out made no difference whatever1 and on taking diagrams with the optical indicator ,i discovered that the exhausting process was divided into equal periods of slight pressure and slight vacuum with an average of zero pressure 7just atmospheric74 ,we have seen in the earlier part of this chapter how the fitting of automatic inlet valves is liable to hamper the engine and reduce its flexibility1 and this impressed me very much with the earlier engines so that at one time ,i adopted dual springs for the inlet valves4 ,these springs were mounted one above the other1 the lower one being much stiffer than the upper one4 ,the idea of the invention was that the weak springs would serve for slow running and all loads up to say half the lift of the valve1 and then the stiffer springs would secure correct action at high speeds4 ,further than this1 ,i had them all coupled on a bar which was controlled from the driver's seat1 and by means of which ,i could cut out the weaker springs or reduce their effect at will4 ,it certainly answered well in the older engines1 but my new engine1 shown in ,fig4 #fe1 was so satisfactory that ,i abandoned the idea4 ,about five different systems of lubrication were experimented with and many lubricating oils4 ,finally1 forced lubrication was employed for all the bearings and a drip sight-feed for the pistons4 ,illustration3 ,,fig4 #fe4--;,,general ,,arrangement ,,of ,,the 8,,kean0 ,,four-,,cylinder ,,high ,,speed ,,high ,,compression ,,duplex ,,two-,,stroke ,,engine ,,employing ,,air ,,scavenging4 ,,in ,,this ,,engine ,,there ,,is ,,no ,,crankchamber ,,compression4 ,much trouble was caused at one time in the new engine by knocking of various kinds1 and many hours were spent in locating these troubles and curing them4 ,the first kind of knocking was most violent and almost made one hold one's breath in anticipation of seeing parts of the engine go skywards4 ,this turned out to be partial seizure of a piston owing to a hard spot in the cylinder4 ,after curing this1 general knocking from all cylinders began1 and was found to result from worn gudgeon pins4 ,these had been mild steel and case-hardened2 they were discarded for ,ubas steel of slightly larger diameter1 and this trouble disappeared4 ,then pre-ignition was discovered4 ,when the magneto was switched off the engine slowed down and nearly stopped1 then began to run on again1 knocking and hammering in a most diabolical manner4 ,all cylinders were taken off again1 all parts ground up1 and corners well rounded off1 but still it continued4 ,at first it seemed to be due to the deflectors1 but on several very careful examinations 7which of course meant dismantling the whole engine every time and removing the cylinders7 no trace of overheating or burning could be found on these or anywhere else in the interior of the cylinder4 ,then the trouble was traced to the electrodes of the sparking plugs4 ,this was followed by two or three weeks' continuous experiments on fitting different types of plugs1 and the same type of plug was tried in four different positions inside the cylinder4 ,then the device of fitting the plugs to an adapter and so keeping them at the top of a small hole instead of projecting into the cylinders was tried4 ,they still showed signs of overheating1 and strange to say no loss of power or flexibility was noticeable4 ,finally1 ,i fitted a water tank on the dashboard and allowed the engine to suck water into the induction pipe while it drew its mixture from the carburettor in the usual manner4 ,i had previously fitted separate drip-feed of water to the air scavenging valves with a view to effecting cooling of the engine1 but abandoned it owing to lack of results4 ,very soon ,i discovered that for every gallon of petrol the engine consumed ,i could let it take nearly half a gallon of water into the induction pipe4 ,the engine ran much quieter and very smoothly1 and for a time ,i thought ,i had succeeded1 although the water gave me trouble in restarting if ,i happened to stop the engine while it was in use4 ,it meant that the water had to be shut off some minutes before the engine was going to be stopped4 ,the day after ,i thought ,i had effected a cure for the pre-ignition intermittent knocking began1 and there was also general knocking always for a second or two when accelerating quickly under load4 ,after much loss of time and the expenditure of a large sum of money on experiments1 ,i persuaded the ,syndicate to let me take some diagrams from the engine with an optical indicator1 and eventually after nine months they consented1 but they would not agree to my taking the engine out of the chassis and putting it on the bench for a proper power test4 ,therefore my diagrams were taken while the engine was in the garage in its chassis1 and the load was applied by the propellor shaft brake1 the shaft itself being withdrawn4 ,anyone who has attempted even in a well-equipped laboratory and with the aid of a proper brake to take diagrams from a petrol engine when the indicator is driven by a flexible shaft1 will understand and appreciate my work in securing thirty photographic records under as many conditions of load and speed4 ,after carefully analyzing my diagrams1 ,i came to the conclusion that the intermittent knocking was undoubtedly flashing back from the exhaust1 and the acceleration knocking was due to a cushion of hot gas which accumulated in the head end of the cylinder at times when the engine speed was low and the load on the engine was heavy4 ,having explained these things to the ,syndicate and pointed out the need for still larger valves1 they set about attempting to raise fresh capital for the final attempt at success4 ,they were not successful1 and up to the present nothing more has been done4 ,the ,syndicate was wound up1 the members drifted apart1 and the patents were allowed to lapse4 ,the engine and chassis were eventually sold1 and are still doing good service somewhere in the ,north of ,england4 ,meantime the writer has not rested1 but has steadily formulated his ideas for the improvement of the engine1 which have resulted in the securing of a fresh patent early this year4 ,in the new engine the charge enters at the head end of the cylinder1 there is a special transverse combustion chamber1 and many improvements are introduced in the scavenging and flow of gases2 also there is no deflector at all on the piston head4 ,funds have not yet been secured to enable an experimental engine to be constructed1 but it is to be hoped they will be forthcoming1 for the benefit of the motor-car industry generally1 as the future undoubtedly lies with the two-stroke4 ,during the whole of this time the writer was engaged as ,chief ,assistant in the ,engineering ,department of ,leeds ,university1 being in charge of the experimental work of the students in the laboratories there4 ,many of the drawings were made by students in their vacation1 and the writer is greatly indebted to his friend1 ,professor ,john ,goodman1 for so kindly allowing him the necessary freedom during vacation times when there is often much miscellaneous work that requires attention4 ,before closing this chapter one may add a few words on carburation and ignition for two-stroke engines4 ,a four-cylinder two-stroke engine should have cranks at right angles to secure the maximum torque on the shaft4 ,looked at in end view the cranks form the four arms of a cross and thus four impulses are given every revolution1 but as the ordinary magneto only gives two sparks in every revolution it must be driven at twice the crankshaft speed4 ,this puts a great strain on the machine at top speed1 and also on the insulation of the windings and the plugs1 so that the plugs require constant attention4 ,magneto troubles were found to be eliminated by the use of the special racing pattern magneto supplied by some manufacturers and the choice of high grade sparking plugs4 ,carburation troubles were not so easily dealt with4 ,a multi-cylinder two-stroke engine should undoubtedly have a multiple jet carburettor and some form of hand-controlled extra-air inlet valve on the induction pipe2 also the mixing chamber of the carburettor should be water-jacketed by hot water4 ,it was also found necessary to fit a hot water-jacket round a portion of the induction pipe1 as the demand for petrol vapour was so great and the rate of evaporation so high that frost readily formed on the induction pipe unless the weather was very warm4 ,the two-stroke engine requires its petrol much faster than the four-stroke1 so that the float of the carburettor should be delicately balanced and the height of the petrol in the jet should be quite level with the top of the orifice1 although this often leads to flooding4 ,reviewing the description of what we have designated the ,kean two-stroke engine1 we may sum up the results of these experiments by saying that the engine could have developed considerably more power than it did had diagrams been taken from it in the first instance and the severe throttling in the carburettor and automatic inlet valves been discovered2 moreover1 the flashing back from the exhaust would have been located much sooner and probably cured by a re-arrangement of the exhaust manifold4 ,if the exhaust manifold had been arranged so that there was a separate branch for at least each pair of cylinders1 it would very likely have been stopped1 or at any rate greatly reduced4 ,but what could not have been altered was the acceleration knocking4 ,it must not be imagined because ,i have been very frank in the criticism of my own work that the engine was a failure2 it was a great success1 but not sufficiently successful to represent an improvement on the best four-stroke practice4 ,the car ran well1 was very reliable and efficient in petrol consumption2 the engine was quiet and extremely flexible2 but it had one very objectionable feature in that every time you pressed the accelerator pedal down sharply1 either to put on a spurt for the purpose of passing slower traffic or in rushing a short gradient1 a peculiar knocking or hammering arose from the engine cylinders--this is what ,i describe as acceleration knocking and must not be confused with the knocking or hammering of a four-stroke engine when labouring on a gradient4 ,my engine would be full of life all the time it was knocking like this1 and gradually as the speed increased the noise would ease-off1 even though no change of gear had been made4 ,the diagrams proved to me that this knocking was due to pre-ignition caused by a cushion of hot gases remaining in the top of the working cylinder1 and in my opinion no alteration of the ports or cylinder head would have influenced this defect to any marked extent2 therefore ,i should never attempt again to feed the new charge in at the bottom end of the cylinder of a two-stroke engine if ,i wished to obtain the maximum amount of power from it4 ,it seems to me that other people must also have been impressed with similar misgivings1 for in one or two types of engine using crankchamber compression we see a special attempt made to overcome it1 although the method adopted leads to a rather undesirable arrangement of the engine mechanism4 ,in the type of engine ,i refer to the charge may be drawn into the crankchamber in the usual manner1 if desired1 but the working cylinder is a casting with two bores having two separate pistons and a common combustion chamber4 ,the charge enters above one piston while the crank is on its bottom dead-centre and is exhausted from the space above the other piston simultaneously1 and the path of the gases is from the inlet port up to the top of ,no4 7#a7 bore1 then down to ,no4 7#b7 bore1 and out of the exhaust4 ,this ensures that there shall be no cushion of hot exhaust gases left in the combustion chamber 7or top end of the cylinder74 ,these engines have given quite good results1 and would be much more extensively used but for the fact that there is double compression to overcome in starting1 and their running torque1 due to the number of impulses given to the crankshaft1 is no better than a four-stroke engine4 ,fig4 #ff shows the arrangement of the cylinders and the path of the gases4 ,a#a and ,a#b are the twin pistons working in the water-jacketed cylinder casting ,b1 and having the common combustion chamber ,c4 ,the connecting rods may drive separate cranks in opposite directions or both be coupled together and work a single crank4 ,it will be seen that in this type of engine the piston does not require any deflector4 ,the simple two-stroke engine described at the beginning of this chapter is often constructed in such a form that no automatic inlet valve is required on the crankchamber4 ,in this case the induction pipe is connected to a third set of ports just below and a little to one side of the inlet ports to the working cylinder1 and these are uncovered by the piston towards the completion of its upstroke1 thus allowing the carburetted air to enter the crankchamber4 ,such an arrangement constitutes a three-port two-stroke engine1 which is of course less efficient than a two-port engine with automatic valve1 but has the great merit that it is entirely valveless1 and therefore extremely simple and cheap to manufacture4 ,it is much used for motor boat work1 both in this country and in ,america1 on account of its relatively low speed of rotation4 ,illustration3 ,,fig4 #ff4--,,twin-,,cylinder ,,two-,,stroke ,,engine ,,with ,,crankchamber ,,compression4 ,,chapter ,,xi ,,horse ,,power ,,and ,,the ,,indicator ,,diagram ,a book on 8,the ,petrol ,engine0 would hardly be complete without some reference to horse-power and the indicator diagram4 ,the following definitions must be carefully studied4 ,work4--,a force is said to do mechanical work when it overcomes a resistance in its own line of action4 ,the line of action of a force is a line indicating the direction in which the force acts4 ,engineers measure work in foot-pound units4 ,the product obtained when we multiply the magnitude of the force or resistance 7in pounds7 by the distance through which it has acted or been overcome 7expressed in feet7 gives the quantity of work done in foot-pounds4 ,example3--,a force of #ej lbs4 is exerted in overcoming a resistance through a distance of #ab feet4 ,find the work done4 ,work done ,force 7in lbs47 ,distance 7in ft47 #ej #ab #fjj ft4 lbs4 ,power4--,the rate at which work is done is a measure of the power exerted4 ,one horse-power is exerted when #cc1jjj foot-pounds of work are done in one minute4 ,the work done per minute 7in ft4 lbs47 divided by #cc1jjj gives the horse-power expended4 ,example3--,to propel a motor-car along a level road at a speed of #cj miles an hour requires a tractive effort or pull of #gj lbs4 if the vehicle weighs one ton4 ,find the horse-power required1 at the road surface4 ,work done per minute in ft4 lbs4 ,horse-power ---------------------------------------- ---------------------- #cc1jjj ,force 7in lbs47 ,distance through which it acts per minute 7in ft74 ---------------------------------------- ---------------------------- #cc1jjj #gj #cj #ebhj ---------------------------- #fj #g #bfd ---------------------------- ------------- #ef #cc1jjj #ccj ,example3--,if the car in the preceding example had to climb a gradient which rose one foot for every four feet traversed by the car1 find the additional horse-power needed to keep up a speed of #cj miles an hour while climbing the gradient4 ,here we have to raise a weight of #a ton vertically upwards through a height equal to one-fourth of the road surface covered1 every minute4 ,additional ,horse-power required 7#cj #ebhj #a7 #bbdj 7lbs47 7----------------- -7 ft4 per min4 7 #fj #d7 ---------------------------------------- ---------------------------------------- ------ #cc1jjj #bbdj #ffj -------------------- #ddh #cc1jjj ,total ,horse-power to climb the gradient of #a in #d at #cj miles an hour #ef #ddh #ejd ,brake ,horse-,power4--,the length of the circumference or boundary line of a circle is #fbh times the length of the radius of the circle or #cad times the length of its diameter4 ,hence1 if an engine exerts a pull of ,p lbs4 at the end of a brake arm of length ,r feet when it is maintaining a speed of ,n revolutions per minute 7we may imagine the brake to be fitted round the rim of the flywheel71 we can calculate the brake horse-power thus3-- ,brake ,horse-,power or ,b4,h4,p4 ,work done on the brake per minute in ft4 lbs4_/#cc1jjj ,hence ,b4,h4,p 7,pull at the end of the brake arm 7in lbs477 7#fbh times the radius of the arm 7in feet77 7the number of revolutions made by the engine 7in one minute77_/#cc1jjj ,p #fbh ,r ,n_/#cc1jjj ,illustration3 ,,fig4 #fg4--,,petrol ,,engine ,,brake4 ,example3--,an engine being tested by a brake applied to the flywheel as shown in the sketch 7,fig4 #fg7 exerts a pull of #ej lbs4 at a speed of #b1jjj revolutions per minute4 ,if the length of brake arm is #cj inches1 calculate the brake horse-power developed4 ,work done per minute #ej #fbh #cj_/ab #bjjj ft4 lbs4 ,b4,h4,p4 #ej #fbh #cj_/ab #bjjj_/cc1jjj #dge ,rated ,horse-,power4--,for taxation purposes the ,treasury makes use of a formula for the rating of petrol engines according to their probable horse-power4 ,this formula is based on a certain speed of the piston which was regarded as a limiting value some years ago 7when the formula was first proposed7 and on the attainment of a certain effective pressure in the cylinder4 ,horse-power from the ,treasury formula #jd d#bn4 ,where d diameter of cylinder in inches1 n number of cylinders4 ,with modern engines much greater horse-power is obtained1 and a near approximation to the true output is obtained by using what is now known as the ,joint ,committee's formula4 ,brake ,horse-,power #jdf n 7d s7 7d - #aah7 ,where d diameter of cylinder in inches4 s length of piston's stroke in inches4 ,this formula is only to be used in an attempt to predict the probable maximum horse-power which any engine will give4 ,it must not be confused with the ordinary brake horse-power formula4 ,example3--,find the probable maximum horse-power of an engine having four cylinders each #c in4 bore and a piston stroke of #d in4 ,what would be its horse-power for taxation purposes8 ,by ,joint ,committee's formula-- ,b4,h4,p4 #jdf #d 7#c #d77c - #aah7 #ahd #g #ahb #bcce ,by ,treasury formula-- ,b4,h4,p #jd #cb #d #jd #i #d #add ,indicated ,horse-,power4--,the horse-power which an indicator would show as being developed inside the cylinder of a petrol engine1 above the piston1 would be called the indicated horse-power1 and should always work out a greater number than the brake horse-power or power available at the engine flywheel1 because some of the power liberated from the combustion of the petrol within the cylinder is lost in friction of the piston and bearings4 ,the ,indicated ,horse-,power or ,i4,h4,p4 ,pe ,a ,l x ,ne_/#cc1jjj4 ,where ,pe mean effective pressure from the diagram1 in lbs4 per sq4 inch4 ,a area of piston in square inches #jghed 7diameter of cylinder7#b ,l length of stroke of piston1 in feet4 ,ne number of power impulses per minute delivered to the crankshaft4 ,since a four-stroke engine gives one power impulse to the crankshaft in every two revolutions1 it follows that ,ne is equal to half the number of revolutions per minute for a single-cylinder engine of that type1 and twice the number of revolutions for a four-cylinder engine4 ,a four-cylinder two-stroke engine might be arranged to give either two or four impulses per revolution of the crankshaft--depending upon the arrangement of the cranks4 ,example3--,a four-cylinder four-stroke engine runs at a speed of #b1jjj revolutions per minute and the mean-effective pressure in the cylinders is #ge lbs4 per square inch4 ,calculate the indicated horse-power if the cylinders are #d in4 #d in4 ,i4,h4,p ,pe ,a ,l ,ne_/#cc1jjj #ge #jghed #db 7#d_/ab7 #djjj_/cc1jjj #ge #abef #djjj_/ii1jjj #ch ,the ,indicator ,diagram4--,at the commencement of this chapter we explained that the work done by a force was measured by multiplying the number representing the magnitude of the force 7in pounds7 by the distance through which it had acted 7measured in feet74 ,this product gave us the quantity of work done in foot-pound units4 ,thus 8quantity of work done0 is really the product of two numbers1 just as the area of a rectangular floor space is measured by length times breadth4 ,in symbols we write ,w ,f ,s where ,f is the magnitude of the force or resistance in pounds and ,s the distance through which it has acted1 in feet4 ,it is interesting to contemplate this symbolical expression ,w ,f ,s together with the expression ,area ,length ,breadth1 because it gives us a new idea for measuring work4 ,imagine a diagram of the kind shown in ,fig4 #fh1 in which the curved line ,,ab has been obtained by plotting values of ,f and ,s for any imaginary case4 ,the diagram is supposed to represent pictorially how the particular force under consideration has varied in magnitude as it has traversed a space represented1 to some scale1 by the length ,,dc4 ,it is clearly seen that the force has been decreasing in an irregular manner from some large value represented by the height ,,da to a small value represented by the height ,,cb4 ,we now proceed to show that the shaded area ,,abcd measures the total amount of work done by this force4 ,illustration3 ,,fig4 #fh4--;,,force-,,space ,,or ,,work ,,diagram4 ,considering for a moment just the small strip efdc of the diagram we see that it is easy to find a rectangle abcd equal in area to it4 ,now the height of this rectangle will be the average value of the force while it traversed the space cd1 and hence the area of the rectangle abcd gives the work done by the force in passing from c to d4 ,similarly by dividing up the whole diagram we would obtain a number of little rectangles each equal in area to the magnitude of the work done from point to point4 ,thus the whole area ,,abcd gives the whole work done4 ,to measure the work done in an engine cylinder we must use some form of indicator4 ,an indicator is an instrument which traces out a diagram on which absciss 7or horizontal distances7 represent displacements of the piston and ordinates 7or vertical distances7 represent the pressures acting on the piston4 ,illustration3 ,,fig4 #fi4--,,petrol ,,engine ,,indicator ,,diagram4 ,,four-,,stroke ,,cycle4 ,ordinary steam engine indicators with pencil motion and paper drum are not suitable for use with fast running petrol engines4 ,the moving parts of these indicators are too heavy and their springs too sluggish in action to keep correct time with these high speed engines4 ,again1 there is too much friction between the pencil and the paper drum1 as well as in the lever joints4 ,therefore special indicators have to be used1 in which the diagram is traced out by a beam of light reflected from a mirror on to a ground glass screen or photographic plate4 ,one corner of the mirror is tilted in time with the movement of the engine piston by means of a special reducing mechanism1 and another corner of the mirror is tilted in a direction at right angles to the first by means of a very short thin rod kept in contact with a metal diaphragm subjected to the pressure of the gases in the engine cylinder4 ,a beam of light is thrown on to the mirror from a lamp1 and after reflection traces out the diagram on the screen or plate4 ,such an instrument would generally be described as a manograph4 ,an indicator diagram from a four-stroke engine is shown in ,fig4 #fi4 ,the line ,,abc represents the suction stroke of the piston during which the pressure of the gases in the cylinder falls a little below that of the atmosphere4 ,atmospheric pressure is shown by the height of the line ,,ll above the base1 or line of zero pressure 7perfect vacuum74 ,the inlet valve can be opened at ,b and closed at ,d after the crank has turned the bottom dead-centre and begun the compression stroke4 ,the line ,,cde represents the compression stroke of the engine1 during which the gases are compressed and their pressure rises4 ,the height of the point ,e above the line ,,ll gives the compression pressure to the scale of the diagram4 ,ignition occurs at ,e1 and results in an instantaneous rise of pressure to ,f due to the explosion1 which is1 however1 quickly followed by expansion to ,g4 ,the exhaust valve opens at ,g1 the gases are released1 and the pressure falls still further to point ,h4 ,the line ,,ha represents the exhaust stroke of the piston1 and the exhaust valve would be closed after the crank had passed its upper dead-centre and commenced the suction stroke4 ,the distance marked 7x7 on the diagram measures the clearance volume 7or volume of the space above the piston containing the valves and referred to as the combustion chamber7 to the same scale that the length of the diagram measures the volumetric displacement of the piston4 ,the volume traced out by the piston during any working stroke is measured by multiplying the area of the piston in square centimetres by the length inches of the stroke in centimetres the product giving us inches the capacity of the cylinder in cubic centimetres4 ,the inches area of the diagram ,,hefg gives the work done during one cycle of operations1 and the area of the small diagram ,,abcd gives the work lost in taking in and expelling the charge4 ,the small area should be subtracted from the large one to get the useful work done per cycle of operations4 ,the area of the diagram ,,hefg may readily be obtained by finding its vertical height at a number of equidistant points1 and from these measurements ascertaining the average or mean height of the diagram4 ,the average height of the diagram 7in inches7 multiplied by its length 7also in inches7 gives the area in square inches4 ,illustration3 ,,fig4 #gj4--;,,indicator ,,diagram ,,from ,a ,,two-,,stroke ,,engine4 ,the average or mean height of the diagram also gives what we term the mean effective pressure acting on the piston1 and constitutes the ,pe of the indicated horse-power formula above4 ,the area ,,abcd is always small and generally neglected with four-stroke engines4 ,there are two separate diagrams for a two-stroke engine4 ,the diagram for the working cylinder is ,a#a;,b#a;,c#a;,d#a in ,fig4 #gj1 and that for the crankchamber is ,e#a;,f#a;,g#a;,h#a4 ,the effective work done per cycle is measured by the difference in the area of these two diagrams4 ,the piston uncovers the exhaust port at ,b#a and closes it again at ,c#a2 it uncovers the inlet port at ,f#a and covers it again at ,g#a4 ,from ,f#a to ,g#a the charge is being delivered from the crankchamber to the working cylinder4 ,the area of the loop ,e#a;,f#a;,g#a;,h#a is larger than the corresponding portion of the four-stroke diagram and should not be neglected4 ,,chapter ,,xii ,,liquid ,,fuels ,important factors in the choice of a liquid fuel for use in portable internal combustion engines are3 7#a7 low cost2 7#b7 ease and safety of transportation or storage2 7#c7 high volatility1 i4e41 readily convertible into vapour2 7#d7 non-corrosive action on metals2 7#e7 high heat efficiency2 7#f7 ability to give satisfactory results in existing types of internal combustion engine4 ,petrol is a liquid fuel composed of carbon 7,c7 and hydrogen 7,h7 in chemical combination4 ,the principal method of producing petrol is by distillation of crude petroleum4 ,the best mixture to use in a petrol engine is one composed of #b cubic feet of petrol vapour to every #ih cubic feet of air4 ,petrol does not require any heat to vaporize it under ordinary atmospheric conditions4 ,pre-ignition of the charge is liable to occur if the compression pressure exceeds #ajj lbs4 per square inch4 ,it does not corrode or deteriorate metal parts1 but leaves a black carbon deposit if not properly burned4 ,its volatility is high and its specific gravity is low1 being about #jga4 ,an average figure for the calorific value of petrol would be #bj1jjj ,b4 ,th4 ,u4 per lb4 ,petrol is very expensive and also needs care in handling4 ,private motorists are not allowed to store petrol or benzol4 ,benzol is a liquid fuel containing more carbon 7,c7 and less hydrogen 7,h7 than petrol4 ,the principal method of obtaining benzol is by distillation of coal tar4 ,the strength of the mixture should be such that a little more air is supplied in proportion to the quantity of fuel used than is required for petrol4 ,generally1 it may be said that when an engine has been running on petrol and is changed over to benzol the size of the carburettor jet orifice should be slightly reduced and the weight of the float increased--no other changes need be made anywhere4 ,benzol is very volatile and also highly dangerous to handle1 on account of its low flash-point4 ,it often contains impurities which attack the metal parts of the engine and gum up the valves4 ,it is more liable to deposit carbon than petrol4 ,benzol attacks rubber1 and paint on coachwork4 ,it is as expensive as petrol at the present time4 ,the specific gravity of benzol may be taken as #jhh and its calorific value as #ai1jjj ,b4 ,th4 ,u4 per lb4 ,it may be compressed above #ajj lbs4 per square inch without pre-igniting4 ,alcohol is a liquid fuel composed of carbon 7,c71 hydrogen 7,h71 and oxygen 7,o74 ,the principal method of obtaining alcohol is from the fermentation of vegetable matter1 such as potatoes1 beetroot1 etc4 ,about #f cubic feet of vaporized alcohol to every #id cubic feet of air should be used4 ,the volatility of alcohol is very poor compared with petrol or benzol1 and it generally contains some water in suspension4 ,it will stand double the compression pressure of petrol without pre-igniting4 ,alcohol is not so liable to deposit carbon as petrol or benzol1 but is very liable to cause rust4 ,it is not obtainable as a fuel in ,great ,britain at present1 owing to the high duty on it4 ,engines for use with alcohol ought really to be specially constructed for the purpose4 ,its calorific value is only #ab1jjj ,b4 ,th4 ,u4 per lb41 and its specific gravity is #jhb4 ,alcohol requires to be heated before it will vaporize1 this heat generally being obtained from the exhaust gases after the engine has been first started up4 ,alcohol is fairly safe to handle or store4 ,paraffin is obtained during the distillation of petrol from crude petroleum1 and consists of carbon 7,c7 and hydrogen 7,h7 in almost the same proportions as petrol4 ,its volatility is low1 and it requires heat to vaporize it4 ,the heat required for vaporization is usually obtained from the exhaust gases after the engine has been got running4 ,in starting up a lamp must be used for heating the vaporizer of the carburettor4 ,paraffin will stand a little higher compression than petrol before pre-igniting4 ,the specific gravity of paraffin may be taken as #jhj and its calorific value as #ah1jjj ,b4 ,th4 ,u4 per lb4 ,it is much cheaper than either petrol or benzol1 being only about one-third of the cost4 ,the chief objections to its use are its smell and the greasy character of the stain left by it on coachwork or clothes2 also the difficulty of having to heat the vaporizing chamber of the carburettor4 ,it is much safer to handle and store than either petrol or benzol1 and requires about the same proportion of air to form an explosive mixture as that given for petrol4 ,the range of variation of strength in the mixture which is permissible with paraffin is much less than with either petrol1 benzol1 or alcohol4 ,alcohol has the greatest range of variation in mixture strength4 ,paraffin is also very liable to deposit carbon1 owing to the small range of variation permissible in the strength of the mixture4 ,thermal ,efficiency4--,in the foregoing notes we have used certain terms which have not previously been explained1 and therefore it is necessary to give one or two definitions4 ,the ,specific ,gravity of a fuel is the ratio of the weight of one gallon of the fuel to the weight of one gallon of water4 ,as a gallon of water weighs #aj lbs41 it will be evident from the above notes that a gallon of petrol only weighs #ga lbs41 whereas a gallon of benzol will weigh #hh lbs4 7approx471 hence it is not surprising to learn that more mileage per gallon is obtained with benzol than with petrol1 even though the calorific value of benzol1 per lb41 is less than that of petrol4 ,sometimes the specific gravity is referred to as the density of the fuel1 but this is only correct when grammes and centimetres are being used4 ,the density of any fuel is the weight of #a cubic foot expressed in pounds or1 in general terms1 the mass of unit volume of the fuel4 ,the density of petrol in ,english units would be about #dd lbs4 per cubic foot4 ,one ,british ,thermal ,unit is the quantity of heat required to raise the temperature of #a lb4 of water by #a degree 7,fahrenheit scale7 when the temperature of the water is about #fj;,f4 ,the ,calorific ,value of any fuel 7reckoned on the ,british system of units7 is the amount of heat 7expressed in ,british ,thermal ,units7 which will be given out by #a lb4 of the fuel when it is completely burned4 ,the liquid fuels we have to deal with are hydrocarbon compounds1 and when completely burned the whole of the carbon is burned to carbon dioxide 7,,co#b7 and the hydrogen to steam 7,h#b,o71 leaving no residue4 ,by means of a calorimeter we can experimentally determine the calorific value of any fuel4 ,it has long been known that work can be turned into heat1 and the petrol engine is a good example of the reverse process which consists in turning heat into work4 ,in a steam engine and boiler plant the heat of the fuel is liberated under the boiler1 and then a portion of it gets transferred to the water in the boiler and forms steam1 which is then taken to the engine and does work in the cylinder1 the whole being a wasteful process4 ,the petrol engine is an internal combustion engine1 or one in which the fuel is burnt inside the engine cylinder itself and converted directly into work4 ,from every ,british ,thermal ,unit of heat liberated by the combustion of the fuel in the cylinder we should be able to get #ggh foot-pounds of work if the thermal 7or heat7 efficiency of the engine was #ajj per cent4 ,the thermal efficiency 77 of any engine may be defined as the ratio which the heat equivalent of the work done per minute by the engine bears to the heat which would be liberated by the complete combustion of the quantity of fuel admitted to the cylinder per minute4 ,thus-- 7,horse-power of the ,engine #cc1jjj7_/ggh ---------------------------------------- ---------------------------------------- -------------------------------------- 7,number of pounds of fuel consumed per minute7 7,calorific ,value of the fuel7 ,example3--,an engine developing #cj horse-power uses #jej lb4 of benzol per minute4 ,what is its thermal efficiency8 ,the calorific value of benzol may be taken as #ai1jjj ,b4 ,th4 ,u4 per lb4 7#cj #cc1jjj_/ggh7_/7jej #ai1jjj7 #jacd1 or #acd per cent4 ,,appendix ,,engine ,,troubles ,many of the troubles that are likely to arise have already been referred to in previous chapters1 but the following additional notes may be found useful4 #a4 ,engine refuses to start4 ,care must be taken to observe exactly what happens1 and one cannot do better than ask oneself mentally some of the following questions4 7a7 ,is the ignition 8on08 ,if a magneto is fitted the earth connexion should be open1 but if a coil and accumulator are fitted the earth connexion should be closed4 7b7 ,is the petrol reaching the carburettor jet8 ,before removing the jet for the purpose of examining and cleaning it1 it would be advisable to ascertain whether the petrol was reaching the float chamber4 ,provided there is a reasonable amount of petrol in the tank and the tap is turned on1 there must be a stoppage either in the petrol filter1 the petrol pipe1 or the bottom portion of the float chamber4 ,examine the filter and float chamber before disconnecting any pipes4 7c7 ,is there a good compression in all the cylinders8 ,if there does not appear to be any compression in any of the cylinders1 it is probable that the carburettor throttle is closed and no air or gas can enter the cylinders4 ,if there is a good compression in some cylinders and a poor one or none at all in others then-- 7#a7 ,one or more of the valves may be held off its seat by dirt1 by distortion1 or by some derangement of the valve gear4 ,examine the valve gear externally1 turning the engine slowly to watch its action4 ,afterwards remove valve caps and inspect valves if necessary4 7#b7 ,one or more of the sparking plugs or valve caps may be short of its washer4 ,in this case the blow will be heard as the engine is turned round by hand4 7#c7 ,a piston may be cracked or broken or a cylinder cracked4 7#d7 ,a cylinder may have got badly worn and the rings on the piston jammed so that they no longer keep it gas-tight4 7d7 ,is the engine very stiff to turn over8 ,stiffness is due as a rule to lack of oil on the cylinder walls1 caused by absence of oil in crankchamber or the film of oil on the cylinder walls having been washed off when priming the engine with petrol in attempting to start it4 ,if a connecting rod is bent1 or the crankshaft distorted or a piston ring broken1 stiffness will also be noted4 ,very often by removing the valve caps and pouring a teaspoonful of oil or paraffin into each cylinder the engine may be freed by vigorously turning the starting handle by hand until the cylinders and pistons are well lubricated4 7e7 ,is there any sign of an attempt to fire the charge such as an occasional puff of smoke from the exhaust or inlet1 or an occasional jerk round of the engine as you turn the starting handle1 or an occasional 8bang0 in the exhaust box8 ,if the ignition is 8on0 and the carburettor jet clear1 the compression good and the engine quite free1 yet there is no sign of a 8fire0 from any of the cylinders1 it is possible that air is leaking into the induction pipe through a faulty joint or any one of the following ignition troubles may have occurred3-- 7f7 ,defective sparking plug or plugs4 ,this may arise from water or oil or dirt between the plug points2 or from faulty insulation in the body of the plug4 ,to test whether the plugs are at fault an easy method is to take a screwdriver with a wooden handle and place the metal blade on the terminal of the plug1 letting the point come about one thirty-second of an inch from the metal of the cylinder or any of the pipes2 when the engine is turned by hand the spark will be seen to pass across this improvised gap if the magneto and leads are in order4 7g7 ,defective electrical connexions4 ,the high tension cables may be broken1 or disconnected1 or short-circuited4 ,the earth wire may be short-circuited 7i4e41 in electrical contact with some other wire or metal fitting74 ,there may be a short-circuit in the ignition switch4 7h7 ,defective magneto or coil4 ,the low tension contact breaker lever may be jammed so that the make and break is inoperative1 or one of the carbon brushes may have got broken4 ,occasionally one finds the magnets of the machine have lost their power2 or there is some electrical defect in the armature or condenser4 ,the battery may have become exhausted4 ,the trembler blade may be stuck up4 ,water may have found its way on to the high tension electrode or into the safety spark gap4 #b4 ,engine starts up fairly well1 runs a little1 and then stops4 ,take care to notice the manner in which the engine runs and stops4 ,note whether it runs regularly or irregularly and for how long a time4 ,if the engine runs regularly with all cylinders firing1 then probably the exhaust is choked or the petrol supply fails4 ,failure of the petrol supply may be due to the use of too small a jet in the carburettor1 too low a level in the float chamber1 or to partial stoppage in the pipe line4 ,another cause of this trouble of intermittent running would sometimes be loss of battery power when using coil ignition1 i4e41 batteries want recharging4 ,if the engine runs irregularly the trouble is probably due to too much oil in the cylinders causing the plugs to misfire1 the presence of water or dirt in the petrol1 a defective valve1 a broken carbon brush1 or poor electrical contact somewhere in the magneto1 the low tension contact breaker 7coil71 or high tension distributor 7coil74 ,to ascertain whether the engine is firing regularly on all cylinders1 or to detect which cylinder is misfiring1 the best procedure is to open the compression taps in turn while the engine is running and in each case speed up the engine while you have the tap open4 ,cylinders which are firing well give a sharp cracking noise1 those which are not firing merely give a hissing noise4 ,if no compression taps are provided1 each plug must be short-circuited to the frame in turn by the screwdriver method given above4 ,the short-circuiting process causes a reduction in engine speed except on that plug which is already not firing4 ,the method is not so good as the compression tap process1 because the plugs often get oiled up during the short-circuiting process and the difficulty is accentuated4 #c4 ,timing the ,ignition4 ,my colleague1 ,mr4 ,oliver ,mitchell1 has pointed out to me that it is often impossible to tell directly when the piston is exactly at the top of its stroke1 and he recommends a study of the accompanying ,valve ,setting ,diagram 7,figure #ga74 ,from this it will be seen that it is sufficiently near to bring the engine first of all to such a position that the exhaust valve has just closed2 then make a chalk mark on the flywheel and give the engine one complete turn round2 the piston will then be in the firing position if the flywheel is turned a shade backwards4 ,another method would be to retard the ignition fully and time it so that the spark occurred one complete revolution after the inlet valve had just commenced to open4 ,when either valve is closed its tappet can be felt to be free1 the amount of freedom depending upon the clearance between the tappet head and valve stem4 ,illustration3 ,,fig4 #ga4--;,,diagram ,,of ,,valve ,,setting4 ,,index ,a ,acceleration1 quick1 #gh -- under load1 #ib ,accessibility1 #ci1 #ej ,accumulator1 #fa ,adapter1 #ib ,adjustable tappet head1 #bi1 #cj ,adjusting screws1 #ai ,advanced ignition1 #ee1 #ef1 #ei ,aeroplane engine cylinder1 #aj1 #af ,air1 #a1 #da1 #db1 #df1 #hg1 #hi1 #aad -- carburetted1 #db1 #ig -- lock1 #gb -- pump1 #ej -- -- hand1 #ej -- scavenging1 #af1 #ce1 #hd1 #he1 #hg1 #hh1 #hi -- to petrol ratio1 #db -- valve1 automatic extra1 #dc1 #di -- velocity1 #df1 #gj -- volume of1 relative to petrol vapour1 #db1 #ajh -- weight of1 relative to petrol vapour1 #db ,alcohol1 properties of1 #aji ,anti-freezing solution1 #gb ,armature of magneto1 #eb1 #ed -- relative speeds of engine and magneto1 #ed1 #ee ,atmospheric pressure1 #c1 #ij ,atomization of petrol1 #dh1 #di ,automatic extra-air valve1 #dc1 #di -- inlet valve1 #hb1 #hd1 #hh ,b ,backfire1 #fb1 #hd ,balance1 perfect1 #gf -- want of1 #ge1 #gf -- weight1 #be ,balancing the crankshaft1 #be1 #bf1 #gf ,barrel of cylinder1 #ab ,base1 oil1 #h1 #dj1 #fe ,battery1 #aaf ,bearings1 main1 #bd1 #fd ,benzol1 properties of1 #de1 #ajh ,blade1 trembler1 #eg ,boiling of water in jackets1 #gb ,boxes1 core1 #aa ,brake1 for petrol engine1 #ajj ,brake horse-power1 #ii ,british thermal unit1 #aaa ,brush1 carbon1 #ec1 #ee1 #aaf ,built-up cylinder1 #af -- flywheel1 #bg ,buoyancy1 #de ,burning1 rate of1 of mixture1 #a1 #eg -- of deflector1 #ia ,bursting of flywheel rim1 #bg ,bush1 phosphor bronze1 #bc ,c ,cables1 high tension1 #fa ,calorific values1 #aaa ,cam1 #cj1 #cc ,camshafts1 #bi1 #cc1 #dj ,cams1 stationary1 for magneto1 #ec ,capacity of cylinder1 #ajf ,caps1 valve1 #ac1 #ca ,carbon brush1 #ec1 #ee1 #aaf -- deposit1 #fc1 #gh ,carburation1 #db1 #id ,carburetted air1 #db1 #ig ,carburettor1 #e1 #h1 #db1 #hb -- jet type1 #db -- multiple jet1 #dg1 #id -- points of a good1 #di -- recent improvements in1 #dg -- spray type1 #db -- surface type1 #db -- wick type1 #db ,castings1 cylinder1 #aa ,cast-in-pairs1 cylinders1 #af ,centrifugal force1 #bg ,chaindrive1 silent1 #ch ,charge1 #c1 #hj ,charging pump1 #hj ,chassis1 #dj1 #ga ,choke tube1 #df1 #dg ,chrome steel1 #bj1 #cf ,circulating water pump1 #h1 #ga ,circulation1 forced1 #ga -- local1 #gc -- pump1 #ga -- thermo-syphon1 #fi ,clearance between piston and cylinder walls1 #ag -- of valve tappet1 #bi -- space1 #d1 #aje1 #ajg ,coil ignition1 #eg1 #ei1 #fa -- -- system1 wiring diagram for1 #fa -- non-trembler1 #ei -- supplementary1 for starting1 #eh -- trembler pattern1 #eg1 #fa ,collector ring1 #ee ,combustion1 #gh -- chamber1 #d1 #if ,compensating jet1 #dh ,compression1 meaning of1 #c -- pressure1 #hb1 #hc1 #aje -- stroke1 #f1 #hj ,cone clutch1 #bg ,connecting rod1 #d1 #ba1 #if -- -- forces acting on1 #bj -- -- phosphor bronze1 #bj1 #bb -- -- steel1 #bc ,consumption of fuel1 #gi -- of oil1 #fg ,contact breaker1 low tension1 #ec -- -- wipe form of1 #eh -- screws1 platinum tipped1 #ec1 #eg ,cooling1 #fi ,core-boxes1 #aa ,core1 iron1 of ignition coil1 #eg ,cost of production1 #bb1 #fd1 #gi ,cotter1 #bi ,crank chamber1 #h1 #ci -- -- gas-tight1 #ha1 #hb1 #if -- cheeks or webs1 #bd -- motor-cycle1 #bc -- pin1 #bd -- radius1 #d -- shaft1 #bc1 #bh1 #gg1 #hi ,crank shaft1 balancing the1 #be1 #gf -- -- vibration of1 #gf -- -- whipping of1 #gf ,cushion of hot gas1 #ic1 #if ,cut-out1 #ij ,cycle1 four-stroke1 #e -- motor1 #aj1 #aa -- ,otto1 #e -- two-stroke1 #hj ,cylinder1 #e1 #i -- aeroplane engine1 #ae1 #af -- air-cooled1 #aa1 #ae -- barrel1 #ab -- built-up1 #af -- castings1 #aa -- head1 detachable1 #cb1 #gh -- jackets1 #ab1 #ae1 #fi -- ,l-headed1 #af -- pump1 #hg1 #hh1 #ajg -- revolving1 #aj -- ,t-headed1 #ae -- water-cooled1 #h1 #cb1 #hb1 #if -- working1 #ha1 #hg1 #ajg ,cylinders1 cast en bloc1 #af1 #gg -- cast in pairs1 #af -- cast separately1 #af -- choosing the number of1 #ge -- firing order of1 #fj ,d ,dead centre1 #d1 #aaf -- gases1 #hc ,defective coil1 #aad1 #aaf -- ignition system1 #aad -- magneto1 #aad1 #aaf -- sparking plug1 #aac1 #aad -- valve1 #aac1 #aad1 #aaf ,deflector1 #ha1 #hg1 #ic1 #if -- overheating of1 #hd1 #ia ,density1 #de1 #aaa ,deposit of carbon1 #fc1 #gh ,description of a typical petrol engine1 #h ,detachable cylinder head1 #cb1 #gh ,devices1 ignition1 #ea ,diagram1 indicator1 #ib1 #ajb -- for four-stroke engine1 #aje -- for two-stroke engine1 #ajf -- for valve setting1 #aaf -- work1 #ajc ,difficulties in starting1 #gb1 #ge1 #ib1 #if1 #aac ,discharge1 spark1 #ea1 #ed1 #eh ,distributor1 high tension1 #eb1 #ec1 #eh ,double sleeve engine1 #cb1 #gh ,down stroke1 #d1 #ha1 #hb ,drawings1 working1 #aa1 #ic ,drip feed1 #fd1 #ij1 #ib ,drive1 silent chain1 #ch ,dual ignition1 #eh -- springs1 #ij ,ducts for oil1 #da ,duplex piston1 #hf ,durability1 #di1 #gi ,e ,earthing wire1 #fj ,eccentric1 #cc1 #cf -- rod1 #cc1 #cf -- sheaves1 #cc1 #cf -- straps1 #cc1 #cf ,economy and durability1 #gi ,efficiency1 thermal1 #aaj1 #aaa -- volumetric1 #hc1 #hf1 #hh ,electric spark1 #ea1 #ed1 #eh ,electrodes of sparking plug1 #ea1 #ia1 #ib ,engine1 four cylinder1 #i1 #gf1 #gg1 #id -- internal combustion1 #aaa -- motor car1 #i -- multi-cylinder1 #gg -- points of a good1 #ge -- single cylinder1 #ge -- six cylinder1 #gf1 #gg -- troubles1 #aac -- two cylinder1 #gf -- two-stroke1 #hj1 #ie ,evaporation1 #a ,exhaust pipe1 #f -- ports1 #ha1 #hh -- -- open1 #ha1 #hh1 #if -- smoky1 #ff -- stroke1 #g1 #ce -- system1 overheating of the1 #eg -- valves1 #e1 #aj1 #cg1 #ha -- valves1 timing of the1 #ce1 #cg1 #gh1 #aaf ,explosion stroke1 #g1 #ba1 #bf1 #ce ,explosive mixtures1 #a1 #ajh1 #aji1 #aaj ,extra-air valve1 #dc1 #di1 #id ,f ,fan1 #gj -- pulley1 #h1 #gj ,feed1 drip1 #fd1 #ij1 #ib ,fibre1 tappet head1 #cj -- wheel1 #ch ,film of oil1 #fe ,filter1 petrol1 #dc ,fins1 heat radiating1 #gj ,firing order of the cylinders1 #fj -- stroke1 #fj ,fixed ignition1 #eg ,flanges1 #ab1 #ac ,flash point of lubricating oils1 #fc1 #fg1 #fh ,flashing back from exhaust1 #hd1 #ib1 #ic1 #ie ,flexibility1 #gg1 #hc1 #ib ,float chamber1 #dc1 #dd1 #id ,flooding1 #de1 #id ,fluctuation of engine speed1 #bg ,flywheel1 #h1 #bf -- built-up1 #bg -- function of1 #bf -- rim1 bursting of1 #bg -- single stamping of steel1 #bh ,force1 #ih -- centrifugal1 #bg ,forced circulation1 #ga -- lubrication1 #fe1 #ij ,forces1 inertia1 #ge -- space diagram1 #ajc ,four cylinder engine1 #i1 #gf1 #gg1 #id -- stroke cycle1 #e ,frequency of vibrations1 #gf ,fuel1 consumption of1 #gi ,fuels1 liquid1 #ajh ,furring of tubes and jacket spaces1 #gc ,g ,gap of sparking plug1 #ea1 #ed ,gas1 compressing the1 #c -- pump1 #hj -- tight crankchamber1 #ha1 #hb1 #if ,gearing1 overhead1 #af ,gears1 helical1 #ch --spur1 #cg1 #ch ,general overheating1 #gb1 #gc --principles1 #a ,gilled tube1 #gj1 #gd ,gills1 #gj ,gravity feed1 #ej ,grease in cylinder jackets1 #gb ,grinding in a valve1 #ca ,gudgeon pin1 #ag1 #ah -- -- wear on1 #ai1 #ij ,guides1 valve stem1 #h1 #ab1 #ac1 #cj ,h ,hand air pump1 #ej ,handle1 starting1 #ga ,head1 adjustable tappet1 #cj -- of water1 #fi1 #ga ,heat efficiency1 #aab -- energy of the petrol mixture1 #i1 #ag1 #aaa -- radiating fins1 #aa1 #gj -- surplus1 #i1 #ag ,helical teeth1 #ch ,high tension cables1 #fa -- -- distributor1 #eb1 #ed1 #eh -- -- magneto1 #h1 #ea1 #eb1 #ed1 #hi -- -- terminals1 #ea1 #eg ,holes1 cotter1 #bi -- oil1 #fc ,honeycomb radiator1 #gj1 #gd ,horse-power1 #ih -- brake1 #ii -- indicated1 #aja -- ,joint ,committee's formula1 #aja -- of car1 #ii -- ,treasury formula1 #aja ,hot-water jacket1 #dc1 #dg1 #id ,hydrogen1 #ajh1 #aji ,i ,idle stroke1 #bf1 #hb ,ignition1 advanced1 #ee1 #ef1 #ei -- coil1 #eg1 #ei1 #fa -- devices1 #ea -- dual1 #eh -- fixed1 #eg -- knock1 #eg1 #hd -- normal1 #ee -- retarded1 #ee1 #ei1 #fb -- synchronized1 #ei1 #fa -- timing the1 #fj1 #fb1 #aaf -- two-point1 #ei ,improved system of splash lubrication1 #fd ,improvements in carburettors1 recent1 #dg ,indicated horse-power1 #aja ,indicator diagram1 #ib1 #ajb -- -- for four-stroke engine1 #aje -- -- for two-stroke engine1 #ajf ,indicator1 optical1 #ib ,induction pipe1 #e1 #h1 #dc1 #hb ,inertia forces1 #ge ,inflammable vapour1 #fc ,injection of water to cylinder1 #ib ,inlet ports1 #ha1 #hh -- valve1 air1 automatic1 #dc1 #di1 #hh -- -- automatic1 for gaseous mixture1 #hb1 #hh -- -- mechanically operated1 #e1 #cj1 #ca -- -- timing the1 #cd1 #cg1 #gh1 #aaf -- water pipe1 #h1 #gj1 #gc ,inspection openings1 #ci ,insulators1 #ea ,internal water cooling1 #ib ,j ,jacket1 cylinder1 #ab1 #ae1 #fi -- hot water1 #dc1 #dg1 #id -- space1 too large1 #gc -- water1 overheating of1 #gb -- -- temperature of1 #gd -- -- weight of1 #gd1 #hi ,jet1 atomizing1 #dh -- compensating1 #dh -- petrol1 #dd1 #df ,jet-in-tube carburettor1 #db ,jigs1 #bd ,jockey pulley1 #ch ,joints1 water-tight1 #aa1 #ae ,journals1 #bd ,k ,kean's two-stroke engine1 #he1 #id ,knock ignition1 #eg1 #gc1 #hd ,knocking1 acceleration1 #ib1 #ic1 #ie -- intermittent1 #hd1 #ib1 #ic -- spasmodic1 #hd1 #ia ,l ,l-headed cylinders1 #af ,lag in opening and closing valves1 #cd -- time1 #ef ,lead of valve1 #ce ,leakage of gas past the piston1 #ah1 #aad ,leaky pistons1 #aad ,liquid fuels1 #ajh -- petrol1 #ajh ,local circulation1 #gc -- overheating1 #gb ,lock1 air1 #gb ,lock nuts1 #bi ,low tension contact breaker1 #eb -- -- terminal1 #eg1 #eh -- torque1 #ge ,lubrication1 forced1 #fe1 #ij -- improved system of splash1 #fd -- splash system of1 #fc ,m ,magneto armature1 relative speeds of1 #ed1 #ee1 #id -- for four cylinder engine1 #eb1 #ed1 #fj -- for six cylinder engine1 #ed -- high tension1 #h1 #ci1 #dj -- ignition system1 wiring diagram for1 #fj -- racing pattern1 #id -- two-stroke engine1 #id ,make and break1 #ec1 #eh1 #fb ,manograph1 #ajd ,materials1 packing1 #ae ,mean effective pressure1 #hi1 #ajg ,mechanically operated valve1 #cj1 #hd ,metal segments of distributor1 #ee ,mild steel1 #bc ,mileage per gallon1 #aaj ,misfiring1 #hd1 #aaf ,mixing chamber1 #dc1 #dg ,mixture1 explosive1 #a1 #ajh1 #aji1 #aaj -- heat energy of the1 #i1 #ag1 #aaa -- strength of the #a1 #db1 #ajh1 #aji1 #aaj -- too weak a1 #df -- weakening the1 #di1 #gc ,momentum1 #ce1 #cf ,monobloc casting1 #gg ,motor car engine1 #i -- cycle1 #aj1 #aa -- -- crank1 #bc ,moulds1 #aa ,multiple jet carburettor1 #dg1 #id ,mushroom type valves1 #e1 #h1 #cj ,n ,natural circulation1 #fi ,needle valve1 #dd ,nickel steel1 #bj1 #cf ,noise from valves1 #cj1 #ci ,non-trembler coil1 #ei ,normal ignition1 #ee ,o ,oil base1 #h1 #dj1 #fe -- consumption of1 #fg -- ducts1 #da -- film1 #fe -- holes1 #fc -- pressure1 #fe1 #fg -- price of1 #fg -- properties of1 #fc -- pump1 #h1 #ci1 #dj1 #fe1 #fg -- -- speed of1 #fg -- troughs1 #fe ,open exhaust port1 #ha1 #hh1 #if ,optical indicator1 #ib ,orifice1 #de1 #gc ,oscillations1 torsional1 of the crankshaft1 #gg ,otto cycle1 #e ,outlet water pipe1 #h1 #gj1 #ga1 #gc ,overflow pipe1 #gb ,overhead gearing1 #af ,overheating of deflector1 #hd1 #ia -- of the exhaust system1 #eg -- general1 #gb1 #gc -- local1 #gb ,overloading the engine1 #ee1 #hi ,p ,packing materials1 #ae -- rings1 #ag1 #ah1 #ha1 #hg1 #ig ,paraffin1 properties of1 #aji ,partial seizure1 #ai1 #cc1 #fc1 #fd1 #ij -- vacuum1 #f1 #df1 #hb1 #ij ,passages1 valve1 #aj ,patterns1 #aa ,perfect balance1 #gf1 #gg -- combustion1 #gh ,periodicity1 #gf1 #gg ,petrol1 consumption of1 #gi -- engine1 description of a typical1 #h -- filter1 #dc -- jet1 #dd1 #df -- mixture1 heat energy of1 #i1 #ag1 #aaa -- pipe1 #dc -- properties of1 #ajh -- supply1 failure of1 #aac -- tank1 #dc -- tap1 #dc -- vapour1 #a1 #db1 #dc1 #hj -- -- ratio of air to1 #db ,phosphor bronze bush1 #bc -- -- connecting rod1 #bb ,pinking1 #gi ,pipe1 exhaust1 #f1 #h -- induction1 #e1 #h1 #dc1 #hb -- inlet water1 #h1 #gj1 #ga1 #gc -- outlet water1 #h1 #gj1 #ga1 #gc -- overflow1 #gb -- transfer1 #hf1 #hg -- vent1 #ci ,piston1 #d1 #ag1 #cb1 #hb1 #if -- duplex1 #hf -- leaky1 #gc1 #aad -- ring1 cast-iron1 #ah1 #hb -- -- steel1 #ai -- seizure of the1 #ai1 #cc -- steel1 #ai -- weight of1 #ai ,pitch of the teeth on a gear wheel1 #ch ,plain tube radiator1 #gd ,platinum tipped contact screws1 #ec1 #eg ,plug1 sparking1 #e1 #h1 #ea1 #ia1 #ib ,points of a good carburettor1 #di -- -- good engine1 #ge ,poppet valve1 #bi1 #gg1 #gi ,ports1 exhaust1 #cc1 #gh1 #ha1 #hh -- inlet1 #cc1 #gh1 #ha1 #hh -- open exhaust1 #ha1 #hh1 #if ,power1 #ih -- stroke1 #g1 #fj1 #hj ,pre-ignition1 #hd1 #ij1 #ib1 #ie1 #ajh1 #aji1 #aaj ,pressure1 atmospheric1 #c1 #ij -- compression1 #c1 #hj1 #hb1 #hc1 #hh1 #aje -- feed1 #ej -- mean-effective1 #hi1 #ajg -- of oil1 #fe1 #fg ,prices of oils1 #fg ,primary winding1 #ec1 #eh ,production1 cost of1 #bb1 #fd1 #gi ,properties of fuels1 #ajh1 #aji1 #aaj -- of oils1 #fc ,pulley1 fan1 #h1 #gj -- jockey1 #ch ,pump1 air1 #ej -- charging1 #hj -- circulating1 #h1 #fg1 #ga -- cylinder1 #hg1 #hh1 #ajg -- gas1 #hj -- hand air1 #ej -- oil1 #h1 #ci1 #dj1 #fe1 #fg -- piston1 #hf -- water1 #h1 #ci1 #ga ,push rod1 #bi ,q ,quick acceleration1 #gh1 #ib -- make and break1 #ec1 #ei1 #fb ,r ,racing pattern magneto1 #id ,radiator1 gilled tube1 #fi -- honeycomb1 #gj1 #gd -- size of1 #ga1 #gb1 #gd1 #hi ,rate of burning1 #a1 #eg ,rated horse-power1 #aja ,ratio of air to petrol vapour1 #db ,recent improvements in carburettors1 #dg ,relative speeds of engine and magneto1 #ed1 #id ,release of gases1 #aje ,relief valves1 #fg ,residue1 #fc ,retarded ignition1 #ee1 #eg1 #ei1 #fb ,revolving cylinders1 #aj ,ring1 packing1 #ag1 #ah1 #ha1 #hg1 #ig -- steel piston1 #ai ,roller1 #bi1 #eh ,rotary valves1 #gi ,s ,sagging of camshaft1 #cf ,scavenging1 #af1 #ce1 #hd1 #he1 #hg1 #hh1hi1 #ic ,scoops1 #fe ,screws1 adjusting1 for gudgeon pin1 #ah -- platinum tipped1 for contact breaker1 #ec1 #eg ,seat of valve1 #ac1 #bi ,segments1 metal1 of distributor1 #ee ,seizure of piston1 #ai1 #cc1 #fc1 #fd1 #ij ,shafts1 eccentric1 #cc ,sheaves1 eccentric1 #cc ,short-circuiting terminal1 #ee ,silence in running1 #gi1 #ib1 #ie ,silencer1 #f1 #hi ,silent chain drive1 #ch ,simple two-stroke engine1 #ha1 #he ,single cylinder engine1 #ge1 #gf -- sleeve valve engine1 #cb -- throw crankshaft1 #bc ,six cylinder engine1 #gf -- -- -- magneto for1 #ed ,sleeve valves1 #cb1 #gg1 #gh ,sleeves1 double1 #cb1 #gh ,slots1 #cb ,smoky exhaust1 #ff ,spark1 electric1 #ea1 #ed1 #eh ,sparking plug1 #e1 #h1 #ac1 #ea1 #ia1 #ib ,spasmodic knocking1 #hd1 #ia ,specific gravity of fuels1 #ajh1 #aji1 #aaj ,speed1 fluctuation of engine1 #bg -- of oil pump1 #fg ,speeds of magneto armature and distributor1 #ed1 #ee1 #id ,splash system of lubrication1 #fc -- -- -- improved1 #fd ,split pin1 #ai ,spray type of carburettor1 #db ,springs1 dual1 for automatic valve1 #ij -- valve1 #h1 #bi1 #ij ,sprocket wheels1 #ch ,spur gears1 #ch ,stampings for connecting rods1 #bb ,starting difficulties1 #gb1 #ge1 #ib1 #if -- handle1 #h1 #ga ,stationary cams for magneto1 #ec ,steel1 chrome nickel and chrome vanadium1 #bj1 #cf -- flywheel1 built-up1 #bg -- -- single stamping1 #bh -- mild1 #bc -- pistons1 #ai -- -- rings1 #ai -- tungsten1 for valves1 #cj -- ,ubas1 #ij ,storage of petrol1 #ajh ,strap1 eccentric1 #cd ,strength and character of spark1 #eh -- of mixture1 #a1 #db1 #ajh1 #aji1 #aaj ,stroke1 meaning of1 #c -- suction1 #f1 #ba1 #ce1 #fj1 #hj ,suction1 meaning of1 #b ,supplementary coil1 for starting1 #eh ,surface carburettor1 #db ,synchronized ignition1 #ei1 #fa ,t ,tank1 petrol1 #dc ,tap1 compression1 #ac -- petrol1 #dc ,tappet head1 #bi1 #cj -- valve1 #h1 #bi ,teeth1 helical1 #ch -- pitch of1 #ch ,temperature of jacket water1 #gd ,terminals1 high tension1 #ea1 #eg -- low tension1 #eg1 #eh ,t-headed cylinder1 #ae ,thermal efficiency1 #aaj1 #aaa -- unit1 ,british1 #aaa ,thermo-syphon circulation1 #fi1 #hi ,three-port two-stroke engine1 #ig ,throttle valve1 #dd1 #dg ,time lag1 #ef ,timing the ignition1 #fj1 #fb1 #aaf -- the inlet valve1 #cd1 #cg1 #gh1 #aaf -- the exhaust valve1 #ce1 #cg1 #gh1 #aaf -- wheels1 #h1 #cg ,too rich a mixture1 #df1 #gh ,too weak a mixture1 #df1 #gc1 #gh ,torque1 low1 #ge ,torsional oscillations of crankshaft1 #gg ,transfer pipe1 #hf1 #hg ,treasury rating for horse-power1 #he1 #aja ,trembler blade1 #eg -- coil1 #eg1 #fa ,troughs1 oil1 #fe ,tube1 amount required for radiator1 #gd -- gilled1 #gd -- plain1 #gd ,tungsten-steel valves1 #cj ,twin piston two-stroke engine1 #if ,two cylinder engine1 #gf ,two-point ignition1 #ei ,two-port two-stroke engine1 #ha1 #he1 #ie ,two-stroke cycle1 #hj1 #hc1 #hg -- engine1 ,kean1 #he1 #id -- -- simple1 #ha1 #he -- -- twin piston1 #if -- -- two-port1 #ha1 #he1 #ie -- -- three-port1 #ig -- -- valveless1 #ig ,u ,ubas steel1 #ij ,unbalanced mass1 #be ,underframe1 #dj ,up-stroke1 #d1 #ha ,v ,vacuum1 partial1 #f1 #df1 #di1 #hb1 #ij ,valve1 automatic inlet1 #hb1 #hd1 #hh -- -- extra air1 #dc1 #di1 #hh -- caps1 #ac1 #ca -- defective1 #aac1 #aad1 #aaf -- exhaust1 #e1 #cg1 #ha -- extra air1 #dc1 #di1 #id -- guides1 #h -- head1 #bi -- inlet1 #c1 #e -- mechanically operated1 #e1 #cj1 #hd -- mushroom type1 #e1 #h1 #cj -- needle1 #dd -- passages1 #aj -- relief1 #fg -- seat1 #ac1 #bi -- springs1 #h1 #bi1 #ij -- stem guides1 #h1 #ab1 #ac1 #bi -- tappet1 #h1 #bi -- throttle1 #dd1 #dg -- timing the exhaust1 #ce1 #cg1 #gh1 #aaf -- -- the inlet1 #cd1 #cg1 #gh1 #aaf -- to grind in1 #ca -- tungsten steel1 #cj ,valves1 noise from1 #cj1 #ci -- poppet1 #bi1 #gg1 #gi -- rotary1 #gi -- sleeve1 #cb1 #gg1 #gi ,valveless two-stroke engine1 #ig ,valve-setting diagram1 #aaf ,vanadium steel1 #bj1 #cf ,vaporization1 #a1 #df1 #dh1 #di1 #id ,vapour1 inflammable1 #fc -- petrol1 #a1 #cc1 #db1 #hj ,velocity of air1 #df1 #gj ,vent pipes1 #ci ,vibration of crankshaft1 #gf ,viscosity1 #fc ,volatility1 #ajh ,volume displaced by piston1 #aje1 #ajf1 #ajg -- of clearance space1 #d1 #aje1 #ajg ,volumetric efficiency1 #hc1 #hf1 #hh ,vulcanite fibre tappet head1 #cj ,w ,washer1 #bi ,waste heat1 #i1 #ag ,water boiling in jackets1 #gb -- circulating pump1 #h1 #fg1 #ga -- cooled cylinder1 #h1 #cb1 #hb1 #if -- cooling1 internal1 #ib -- head of1 #fi1 #ga -- hot1 for jacket1 #dc1 #dg1 #id -- injection1 #ib -- jacket1 #aj1 #ab1 #gj1 #gb1 #gc1 #if -- pipe1 inlet1 #h1 #fi1 #gj1 #ga1 #gc -- -- outlet1 #h1 #fi1 #gj1 #ga1 #gc -- pump1 #h1 #ci1 #dj1 #gb ,water-tight joint1 #aa1 #ae ,weakening the mixture1 #di1 #gc ,wear on gudgeon pins1 #ai1 #ij ,webs1 crank1 #bd ,weight of piston1 #ai -- of water in radiator1 #gd1 #hi ,weights1 balance1 #be ,wheels1 fibre1 for timing gear1 #ch -- sprocket1 for chain1 #ch -- timing1 #h1 #cd ,whipping of crankshaft1 #gf ,wick type of carburettor1 #db ,winding1 primary or low tension1 #ec1 #eh1 #fa -- secondary or high tension1 #ec1 #eh ,wipe form of contact breaker1 #eh ,wire1 earthing1 #fj ,wiring diagram for coil ignition system1 #fa -- -- for magneto ignition system1 #fj ,work1 #ih -- diagram1 #ajc ,working cylinder1 #ha1 #hg1 #ajg -- drawings1 #aa1 #ic ,wrist pin1 #ah 7,,pr4 #acae47 ,butler ,tanner ,frome and ,london 99 99 99 99 99 ,transcriber's ,notes ,obvious typographical errors have been silently corrected4 ,variations in hyphenation have been standardised but all other spelling and punctuation remains unchanged4 ,italics are represented thus italic1 bold thus bold and underlining thus underline4 ,in several of the equations the final answer was presented in bold text4 ,to avoid confusion with the mathematics this has not been indicated4