,,gas ,,and ,,oil ,,engines ,,simply ,,explained ,an ,elementary ,instruction ,book for ,amateurs and ,engine ,attendants ,,by ,,walter ,c4 ,,runciman ,,fully ,,illustrated ,,london ,model ,engineer ,series4 ,the ,model ,engineer ,series1 no4 #bf4 #aije ,,contents ,,chap4 ,,page ,,preface #e ,i4 ,,introductory #g ,,ii4 ,,the ,,component ,,parts ,,of ,,an ,,engine #ac ,,iii4 ,,how ,a ,,gas ,,engine ,,works #bb ,,iv4 ,,ignition ,,devices #cc ,v4 ,,magneto ,,ignition #dg ,,vi4 ,,governing #ea ,,vii4 ,,cams ,,and ,,valve ,,settings #fc ,,viii4 ,,oil ,,engines #ha ,,preface ,my object in placing this handbook before the reader is to provide him with a simple and straightforward explanation of how and why a gas engine1 or an oil engine1 works4 ,the main features and peculiarities in the construction of these engines are described1 while the methods and precautions necessary to arrive at desirable results are detailed as fully as the limited space permits4 ,i have aimed at supplying just that information which my experience shows is most needed by the user and by the amateur builder of small power engines4 ,in place of giving a mere list of common engine troubles and their remedies1 ,i have thought it better to endeavour to explain thoroughly the fundamental principles and essentials of good running1 so that should any difficulty arise1 the engine attendant will be able to reason out for himself the cause of the trouble1 and will thus know the proper remedy to apply4 ,this will give him a command over his engine which should render him equal to any emergency4 ,,walter ,c4 ,,runciman4 ,,london1 ,e4,c4 ,,gas ,,and ,,oil ,,engines ,,simply ,,explained ,,chapter ,i ,,introductory ,the history of the gas engine goes back a long way1 and the history of the internal combustion engine proper further still4 ,it will be interesting to recount the main points in the history of the development of the class of engine we shall deal with in the following pages1 in order to show what huge strides were made soon after the correct and most workable theory had been formulated4 ,in #afgh ,abbe ,hautefeuille explained how a machine could be constructed to work with gunpowder as fuel4 ,his arrangement was to explode the gunpowder in a closed vessel provided with valves1 and cool the products of combustion1 and so cause a partial vacuum to be formed4 ,by the aid of such a machine1 water could be raised4 ,this inventor1 however1 does not seem to have carried out any experiments4 ,in #afhe ,huyghens designed another powder machine2 and ,papin1 in #afhh1 described a similar machine1 which was provided with regular valves1 as devised by himself1 in the ,proceedings of the ,leipsic ,academy1 #afhh4 ,from this time until #agia1 when ,john ,barber took out a patent for the production of force by the combustion of hydrocarbon in air1 practically no advancement was made4 ,the latter patent1 curiously enough1 comprised a very primitive form of rotary engine4 ,barber proposed to turn coal1 oil1 or other combustible stuff into gas by means of external firing1 and then to mix the gases so produced with air in a vessel called the exploder4 ,this mixture was then ignited as it issued from the vessel1 and the ensuing flash caused a paddle-wheel to rotate4 ,mention is also made that it was an object to inject a little water into the exploder1 in order to strengthen the force of the flash4 ,robert ,street's patent of #agid mentions a piston engine1 in the cylinder of which1 coal tar1 spirit1 or turpentine was vaporised1 the gases being ignited by a light burning outside the cylinder4 ,the piston in this engine was thrown upwards1 this in turn forcing a pump piston down which did work in raising water4 ,this was the first real gas engine1 though it was crude and very imperfectly arranged4 ,in #ahja ,franzose ,lebon described a machine to be driven by means of coal-gas4 ,two pumps were used to compress air and gas1 and the mixture was fired1 as recommended by the inventor1 by an electric spark1 and drove a piston in a double-working cylinder4 ,the atmospheric engine of ,samuel ,brown1 #ahbc1 had a piston working in a cylinder into which gas was introduced1 and the latter1 being ignited1 expanded the air in cylinder whilst burning like a flame4 ,the fly-wheel carried the piston up to the top of its stroke1 then water was used to cool the burnt gases1 which also escaped through valves1 the latter closing when the piston had reached the top of its stroke4 ,a partial vacuum was formed1 and the atmospheric pressure did work on the piston on its down stroke4 ,a number of cylinders were required in this engine1 three being shown in the specification all connected to the same crank-shaft4 ,according to the ,mechanic's ,magazine1 such an engine with a complete gas generating plant was fitted to a boat which ran as an experiment upon the ,thames4 ,a two-cylinder engine working on to a beam was built in ,paris1 but no useful results were obtained4 ,wright's engine of #ahcc used a mixture of combustible gas and air1 which operated like steam in a steam engine4 ,this engine had a water-jacket1 centrifugal governor1 and flame ignition4 ,in #ahch ,barnett applied the principle of compression to a single-acting engine4 ,he also employed a gas and air pump1 which were placed respectively on either side of the engine cylinder1 communication being established between the receiver into which the pumps delivered and the working cylinder as the charge was fired4 ,the double-acting engines which ,barnett devised later were not so successful4 ,from this time to about #ahfj very few practical developments are recorded4 ,a number of ,french and ,english patents were taken out1 referring to hydrogen motors1 but are not of much practical value4 ,lenoir's patent1 dating from #bdth ,january #ahfj1 refers to a form of engine which received considerable commercial support1 and consequently became very popular4 ,a manufacturer1 named ,marinoni1 built several of these engines1 which were set to work in ,paris in a short time4 ,then1 due to sudden demand1 the ,lenoir ,company was formed to undertake the manufacture of these engines4 ,it was claimed that a #d-;horse-power engine could be run at a cost of #c4d shillings per day1 or just one half the cost of a steam engine using #i4i pounds of coal per horse-power per hour4 ,many similar exaggerated accounts of their economy in consumption were circulated1 and the public1 on the strength of these figures1 bought4 ,it was understood that #ag4f cubic ft4 of gas were required per horse-power per hour1 but it was found that as much as #aje cubic ft4 were often consumed4 ,the discrepancy between the stated figures and the actual performance of the engine was a disappointment to the using public1 and1 as a result1 the ,lenoir engine got a bad name4 ,hugon1 director of the ,parisian gas-works1 who1 together with ,reithmann1 a watchmaker of ,muenich1 hotly contested ,lenoir's priority to this invention1 brought out a modification of this engine4 ,he cooled the cylinder by injecting water as well as using a water-jacket1 and used flame instead of electric ignition4 ,the consumption was now brought down to #hg4e cubic ft4 ,at the second ,parisian ,international ,exhibition1 #ahfg1 an atmospheric engine1 invented by ,otto ,langen about this time1 was shown4 ,in this engine a free piston was used in a vertical cylinder1 the former being thrown up by the force of the explosion4 ,the only work done on the up-stroke was that to overcome the weight of the piston and piston rod1 and the latter being made in the form of a rack1 engaged with a toothed wheel on the axle as the piston descended1 causing the fly-wheel and pulley to rotate4 ,barsanti and ,matteucci were engaged in devising and experimenting with an engine very similar to this some years before1 but ,otto ,langen1 no doubt1 worked quite independently4 ,barsanti's engine never became a commercial article2 while ,otto ,langen's firm1 it is said1 held their own for ten years1 and turned out about #djjj engines4 ,in #ahfb the ,french engineer1 ,beau de ,rochas1 laid down the necessary conditions which must prevail in order to obtain maximum efficiency4 ,his patent says there are four conditions for perfectly utilising the force of expansion of gas in an engine4 7#a7 ,largest possible cylinder volume contained by a minimum of surface4 7#b7 ,the highest possible speed of working4 7#c7 ,maximum expansion4 7#d7 ,maximum pressure at beginning of expansion4 ,these are the conditions and principles1 briefly stated1 that combine to form the now well-known cycle upon which most gas engines work at the present time4 ,it was not until #ahgf1 fifteen years after these principles had been enumerated1 that ,otto carried them into practical effect when he brought out a new type of engine1 with compression before ignition1 higher piston speed1 more rapid expansion1 and a general reduction of dimensions for a given power4 ,due to this achievement1 the cycle above referred to has always been termed the ,otto cycle4 ,,chapter ,,ii ,,the ,,component ,,parts ,,of ,,an ,,engine ,having recounted very briefly the chief points in the development of the gas engine from its beginning1 we may proceed to deal with matters of perhaps more practical interest to those who we are assuming have had little or no actual experience in making or working internal combustion engines4 ,the modern gas engine comprises comparatively few parts4 ,apart from the two main castings--the bed and cylinder--a small engine1 generally speaking1 consists of four fundamental members1 viz41 the valves and their operating mechanism1 the cams and levers2 the ignition device for firing the charge2 and the governing mechanism for regulating the supply and admission of the explosive charge4 ,there are innumerable designs of each one of these parts1 and no two makes are precisely alike in detail1 as every maker employs his own method of achieving the same end1 namely1 the production of an engine which comprises maximum efficiency with a minimum of wear and tear and attention4 ,therefore1 before dealing with each of these primary parts in an arbitrary manner1 and with the cycle of operations in detail1 we propose to make the reader familiar with the general arrangement and method of working which usually obtains in the smaller power engines4 ,in the following illustrations these parts are shown4 ,a 7fig4 #a7 is the ignition device which carries the ignition tube to fire the charge4 ,h and ,i 7fig4 #b7 are the main valves1 and ,,gc 7fig4 #a47 is the gas-cock4 ,the side or cam shaft ,n 7sometimes called the #b to #a shaft71 the cams which move the levers ,m1 the latter in turn operating the valves1 and causing them to open and close at the proper time1 are shown in fig4 #aa4 ,a bracket bolted up to the side of cylinder forms a bearing for one end of the side shaft1 and also carries a spindle at its lower end on which the levers oscillate1 transmitting the motion imparted to them by the cams to the valves4 ,the main cylinder casting and the bed need no description4 ,in some cases the bed is in two portions1 though now a great many makers are discarding the lower portion altogether1 having found that it is cheaper1 and quite as satisfactory1 to use a built-up foundation instead1 and1 if necessary1 to cut a trough for the fly-wheel to run it4 ,this arrangement1 however1 only obtains where larger engines are concerned4 ,a half-compression handle by which the exhaust cam is moved laterally on the side shaft as required is not needed on very small engines4 ,illustration3 ,,fig4 #a4--;,general ,arrangement of a ,gas ,engine and ,accessories4 ,further reference will be made to this in another chapter1 and1 although this is not a necessity on a small engine1 it is always employed on engines over #b ,b4,h4,p4 ,in fig4 #a1 ,,hw is the cooling water outlet and ,,cw the inlet4 ,a small drain cock is shown at ,,dc1 through which the water in the cylinder water-jacket may be drawn off when required4 ,the pipes leading to the inlet and outlet of this supply are connected to the cooling water tank by means of a couple of broad1 flat nuts and lead washers1 one inside and the other outside the tank1 the latter1 when clamped up well1 making a perfectly water-tight joint4 ,the outlet pipe making an acute angle with the side of tank1 the washers used there should be wedge-shape in section4 ,it is also desirable to fit a stop-cock ,,sc1 so that the pipes can be disconnected from the engine entirely1 or the water-jacket emptied without running the whole of the water out of the tank4 ,the exhaust pipe ,,ep is made up of gas-barrel4 ,it should lead from the engine to the silencer or exhaust box 7if one is found to be necessary7 as directly as possible1 i4e41 with no more bends than are needed1 and what there are should not be acute4 ,the silencer can be inside or outside the engine-room1 whichever is most convenient2 but both it and the exhaust piping should be kept from all direct contact with wood-work1 and at the same time in a readily accessible position4 ,beyond the exhaust-pipe and box and the water-tank1 the gas bag ,,gb and gas meter 7where small powers are concerned1 the ordinary house or workshop lighting meter may be used without inconvenience7 are the only other accessories which are included in a small installation4 ,illustration3 ,,fig4 #b4--;,a ,section of a ,gas ,engine4 ,fig4 #b gives a sectional view1 showing the cylinder and liner4 ,the latter is a very desirable feature in any type of gas engine1 but especially in the larger sizes2 for at any future time1 should it be found necessary to re-bore the liner1 it can be removed with comparative ease1 and is1 moreover1 more readily dealt with in the lathe than the whole cylinder casting would be4 ,the liner is virtually a cast-iron tube1 with a specially shaped flange at either end4 ,at the back end the joint between it and the cylinder casting has to be very carefully made4 ,this is a water and explosion joint2 hence it has not only to prevent water entering the cylinder from the water-jacket1 but also to be sufficiently strong to withstand the pressure generated in the cylinder when the charge is fired4 ,for this purpose specially prepared coppered asbestos rings are used1 which will stand both water and intense heat4 ,sometimes a copper ring alone is employed to make the joint4 ,at the front end the liner is just a good fit1 and enters the bed easily1 and a couple of bolts fitted in corresponding lugs on the liner1 pass through the back end of cylinder casting1 so that by tightening up these the joint at back end is made secure4 ,a small groove is cut on a flange1 and a rubber ring1 of about #a_/d-;in4 sectional diameter1 is inserted here when the liner is fitted into the cylinder casting4 ,this makes the water-jacket joint at the front end4 ,illustration3 ,,fig4 #c4 ,illustration3 ,,fig4 #e4 ,illustration3 ,,fig4 #d4 ,lugs are provided on the bed and cylinder castings1 and are bored to receive steel bolts--three are sufficient1 provided the metal in and around these lugs is not pinched4 ,in some cases a continuous flange is provided on both bed and cylinder1 and a number of bolts inserted all the way round4 ,this1 however1 is unnecessary1 and has a somewhat clumsy appearance4 ,when these bolts are tightened up1 the cylinder and liner are clamped firmly to the bed2 but the liner being free at the open end1 can expand longitudinally without causing stresses in the cylinder casting4 ,the combustion chamber ,k is virtually part of the cylinder1 and has approximately equal to one-fourth the total volume of the cylinder4 ,the shape varies somewhat in different makes of engines2 in some it is rectangular1 with all the corners well rounded off2 in others it is practically a continuation of the cylinder1 i4e41 it is circular in cross-section1 with the back end more or less spherical2 while1 again1 it is made slightly oval in cross-section2 but in every case the corners should be well curved and rounded off1 so that there is no one part which is liable to become heated disproportionately with the rest of the casting2 in fact1 in the whole cylinder casting there should be no sudden change1 but a uniformity in the thickness of the metal employed4 ,this point should be carefully remembered1 although it applies more particularly to those parts of the casting subjected to higher temperatures than the rest4 ,the main bearings are usually of brass or gun-metal1 and are adjusted for running in the same manner as any steam or other engines would be4 ,the brasses are in halves1 and are held down by the cast-iron caps1 as shown in fig4 #a4 ,these bearings require extremely little attention1 and do not show the wear and tear of running nearly so soon as the connecting-rod brasses4 ,these1 too1 are usually of brass or gun-metal2 but there are various forms of construction employed in connection with the back end or piston pin bearings4 ,on very small engines the connecting rod is swollen at the back end in the forging1 and then machined up and drilled1 as shown in fig4 #c4 ,in this hole the brasses are inserted after being scraped up to a good fit on the piston pin4 ,a flat is cut on one of the brasses1 and a set screw is fitted1 as shown1 to prevent any movement of the latter after the final adjustment has been made4 ,a lock nut should be used in conjunction with this set screw4 ,another method1 and one more generally used on larger engines1 is shown in fig4 #d4 ,in this case the brasses are larger than in the former1 where they are virtually a split bush2 here they have holes drilled in them to take the bolts1 the latter usually and preferably being turned up to the shape shown in fig4 #e4 ,,chapter ,,iii ,,how ,a ,,gas ,,engine ,,works ,the gas engine of the present day1 although from a structural point of view is very different to the early engine1 or even that of fifteen years ago1 is1 in respect to the principle upon which it works1 very similar4 ,the greater number of smaller power engines in use in this country work on what is known as the ,otto or four-cycle principle2 and it is with this class of engine we propose to deal4 ,reference to the various diagrams in the text will help considerably1 and make it an easy matter for any reader hitherto totally unacquainted with such engines to see why and how they work4 ,coal-gas consists primarily of five other gases1 mixed together in certain proportions1 these proportions varying slightly in different parts of the country3--,hydrogen 7,h71 #ej2 marsh gas 7,,ch#d71 #ch2 carbon-monoxide1 #d2 olefines 7,c#f;,h#d71 #d2 nitrogen 7,n71 #d4 ,gas alone is not explosive2 and before any practical use can be made of it1 a considerable quantity of air has to be added1 diluting it down to approximately ten parts air to one of pure gas4 ,this mixture is now highly explosive4 ,the reader will do well to bear these facts constantly in mind1 especially when he is repairing1 adjusting1 or experimenting with a gas engine4 ,we wish to emphasise this at the outset1 because a consideration of these facts will keep cropping up throughout all our dealings with the gas engine1 and if once a fairly clear conception is obtained of how gas will behave under certain and various conditions1 half1 or even more than half1 our troubles will disappear2 the cry that the gas engine has gone wrong will be heard less often1 and users would soon learn that the gas engine is in reality as worthy of their confidence as any other form of power generator in common use4 ,but to revert to the explanation of the cycle of operations4 ,the cycle is completed in four strokes of the piston1 i4e41 two revolutions of the crank shaft4 ,at the commencement of the first out-stroke 7the charging or suction stroke7 gas and air are admitted to the cylinder through the respective valves 7fig4 #f71 and continue to be drawn in by what may be termed the sucking action of the piston1 until the completion of this stroke 7the precise position of the closing and opening of the valves will be referred to later on74 ,the next stroke 7fig4 #g7 is the compression stroke4 ,all the valves are closed whilst the piston moves inwards1 compressing the gases1 until at the end of this stroke1 and at the instant of maximum compression1 the highly explosive charge is fired by means of the hot tube or an electric spark1 as the case may be4 ,the ensuing stroke--the second out-stroke of the cycle--is the result of the explosion1 the expanding gases driving the piston rapidly before them2 this1 then1 is the expansion1 or working stroke 7fig4 #h47 ,illustration3 ,,fig4 #f4--;,commencement of first out-stroke suction or charging stroke4 ,gas and air valve about to open4 ,illustration3 ,,fig4 #g4--;,compression stroke1 during which all valves remain closed4 ,during the last--the second inward--stroke 7fig4 #i7 the exhaust valve is opened1 and the returning piston sweeps all the burnt gases 7the product of combustion7 out into the exhaust pipe and so into the atmosphere4 ,this completes the cycle1 and the piston1 crank1 and valves are in the same relative positions as formerly1 and the same series of operations is repeated again and again4 ,of course1 it is not always the case that both air and gas valve are opened on the charging stroke2 that depends upon the method employed to govern the speed of the engine4 ,supposing it were governed on the hit and miss principle 7to be explained hereafter71 the gas valve would be allowed to remain closed during the charging stroke1 and air alone would be drawn into the cylinder1 then compressed1 but not being explosive would simply expand again on the working stroke1 giving back nearly all the energy which was absorbed in compressing it1 and finally be exhausted in the same manner as the burnt gases are4 ,illustration3 ,,fig4 #h4--,second out stroke1 showing position of valves during working stroke4 ,illustration3 ,,fig4 #i4--,second inward stroke1 showing position of valves during the exhaust stroke4 ,illustration3 ,,fig4 #aj4--;,first out-stroke1 showing position of valves during the charging stroke4 ,fig4 #aj shows diagrammatically the position of crank1 piston1 and valves during the charging stroke4 ,illustration3 ,,fig4 #aa4--;,cross ,section of ,cylinder4 ,in figs4 #a and #b we gave drawings of two gas engines1 which are typical examples of modern practice4 ,huge strides have been made in recent years in gas-engine work1 as regards both workmanship and efficiency1 so that to-day we have in the gas engine a machine whose mechanical efficiency compares favourably with that of any other power generator1 and whose thermal efficiency is very much greater4 ,illustration3 ,,fig4 #ab4--,longitudinal ,section of ,cylinder4 ,figs4 #aa and #ab show respectively a sectional end and side elevation of the cylinder1 from which it will not be difficult for the reader1 however unacquainted he may be with gas-engine work1 to see how the various requirements and peculiarities of the engine should be considered and provided for4 ,a most important desideratum in any machine or engine is that it shall be as simple in construction as ever possible2 complicated mechanism should only be introduced when such addition or complication compensates adequately for what must necessarily be a higher first cost1 and incidentally the greater wear and tear and attention involved4 ,figs4 #aa and #ab show what has been done to simplify the construction of the gas engine in recent years4 ,the main feature in this case is the very get-at-able position of the two main valves--the air valve ,f and the exhaust ,e4 ,these valves1 as may be seen from the drawing1 are capable of withdrawal after the cover of the combustion chamber has been removed4 ,the latter is an iron casting1 shaped and faced up to make an absolutely tight joint2 no asbestos or any packing is used to make this joint--and is held in place by four studs1 as shown4 ,thus1 all that is necessary is to remove the four nuts1 lift the cover off1 then pull out the pins which keep the spiral springs in position1 and withdraw the valves4 ,the latter are seated direct on to the metal of the cylinder casting1 the gun-metal bushes ,a and ,b acting as guides4 ,further reference to ,a 7the mixer71 which serves a twofold purpose1 will be made later on4 ,the gas valve and cock are mounted in a separate casting1 which is carried by a couple of studs1 the joint between this and cylinder being made with a piece of rubber insertion4 ,the gas enters at the gas-cock1 passes through the valve and port ,g1 and round the annular space in the bush or mixer ,a1 previously mentioned1 and thence through a number of small holes in same1 immediately below the seat of the air valve ,f4 ,at the same time1 pure air is drawn in via the air box 7as explained hereafter71 through port ,l 7fig4 #aa71 and thence up the centre of bush ,a and over the small holes through which the gas is flowing4 ,the two then thoroughly mix and enter the combustion chamber together as the air valve ,f is opened4 ,this device produces a perfectly homogeneous mixture1 which conduces in no small measure to perfect combustion when the explosion takes place1 and upon which1 to a very great extent1 depends the efficiency of the engine4 ,besides possible loss in this direction1 however1 there is another source of waste which cannot be eliminated1 and that is the heat taken away by the cooling water which surrounds the cylinder4 ,as this loss is inevitable1 the best thing we can do is to make it as small as possible4 ,theoretically1 it would be no small advantage if we could work at very much higher temperatures than we do at the present time1 and it is only certain mechanical difficulties which bar the way and so effectually prevent the already high thermal efficiency of the engine being greatly increased4 ,it is no easy matter to overcome these difficulties completely1 but improvements in this direction are continually being made1 so that troubles which attended the gas-engine user years ago no longer exist4 ,all that we require of the cooling water is that it shall keep certain working parts of the engine at a reasonable temperature2 for instance1 the cylinder must not be so hot as to deprive the lubricating oil of its property to lubricate1 neither must the exhaust valve become so hot as to cause it to seize in the bush and stick up2 but1 beyond such considerations as these1 the higher the temperature is at the commencement of each explosion the more efficient will the engine be4 ,the object1 then1 is to do as little cooling as possible1 and to apply the cooling effect at the right parts2 hence the passages and chambers through which the cooling water circulates should be so arranged that those which require to be kept at a low temperature are in close proximity to the cooling water4 ,on some of the engines of days gone by1 the exhaust valve was carried in a large iron casting1 this in turn being bolted to the cylinder casting and communicating with the combustion chamber by means of a port4 ,such an arrangement was found to be not only clumsy but inefficient2 the water passages were small and difficult to get at2 they readily furred up2 and moreover1 the joint between this casting and the cylinder was necessarily a water and explosion joint1 and the fewer we have of these the better4 ,the method--if it may be called a method--of overcoming or preventing the exhaust valve becoming too hot is1 in the case of figs4 #aa and #ab1 simply one of judicious arrangement and design4 ,the cooling water enters by the inlet ,k 7fig4 #aa71 and circulates round the exhaust valve port ,x and valve ,e immediately1 before becoming heated1 thus keeping the hottest of the working parts of the engine at a suitable temperature2 and the valve seat1 being in direct metallic communication with the cold water1 does not become burnt or pitted4 ,on the other side of the exhaust valve we have the air valve and its passages1 through which cool air is continually being drawn2 this also helps to keep the exhaust valve cool4 ,from this1 then1 we may conclude that overheating of the cylinder will not occur under normal conditions1 given an engine of good design2 but1 if this trouble does arise1 we may safely look first of all for some defect in the cooling water circulation4 ,some waters contain a greater amount of impurities than others1 and consequently the water space may furr up more rapidly in one district than in another4 ,but this deposit1 even under the worst conditions1 accumulates very slowly1 and the operation of cleaning out the water-jacket is a very infrequent necessity4 ,the exhaust valve1 however1 may become overheated if it is allowed to get into bad condition1 i4e41 leaky4 ,its seat should be well looked after1 or the hot gases will blow past when it is presumably shut2 and if this defect1 slight though it may be to begin with1 is allowed to develop1 both the seat1 the valve head1 and the spindle will become burnt away and pitted1 perhaps badly1 due to the excessive heat4 ,,chapter ,,iv ,,ignition ,,devices ,the ignition devices commonly employed may be divided into three main classes--the metal tube1 the porcelain tube1 and the electric ignition4 ,these again may be subdivided3 ,the first being either iron or nickel 7hecknum as they are sometimes called72 the second are of two kinds--single-ended and double-ended2 and the third takes many forms which many of my readers are possibly well acquainted with1 such as the magneto1 the induction coil and trembler1 and the high-tension magneto ignition1 the latter device having been used successfully on various occasions1 though not yet universally adopted4 ,the first-named have one or two advantages over the nickel tube4 ,they are very inexpensive1 and are easily heated to the required temperature2 moreover1 they can be made at home1 should occasion demand4 ,on the other hand1 they are not so durable1 have a very uncertain life1 and consequently need renewing frequently--their average life being not more than #fj working hours4 ,fig4 #ac gives an outline drawing of an iron tube1 with its burner and chimney fixed in position4 ,the tube is very similar to a piece of #a_/d-;in4 gas-barrel1 closed up at one end and a taper thread 7#a_/d-;in4 gas7 cut on the other2 in fact1 gas-barrel may be used for making these tubes at home--and measure about #g or #h in4 over all ,it is screwed into a firing block1 which in turn is screwed into the combustion chamber end1 so that when right home it is in such position that the tube stands quite vertical4 ,the section of the tube1 fig4 #ac1 shows the condition it gets into after having been in use some time4 ,the bore1 it will be seen1 has become almost completely closed up1 so that there is practically no communication between the hot part of the tube and the combustion chamber4 ,this closing up of the bore is very gradual1 and it is in the early stages of this process that erratic firing is likely to occur2 sometimes the charge will be successfully fired and sometimes not4 ,it may be as well to mention here that the length of the tube1 although to a certain extent immaterial1 should neither be excessively long nor abnormally short1 the precise length varying with the size of the engine4 ,a #a_/d-;in4 tube1 #h ins4 long1 may be used successfully on engines ranging from #a_/b to #f horse-power1 provided a suitable burner is fitted enabling the tube to be heated at any required spot4 ,after the first charge has been fired1 and the exhaust takes place1 practically all the burnt gases are cleared out of the cylinder1 but a small amount of these will generally remain in the tube and the bore of the firing block4 ,on the ensuing compression stroke these inert gases are compressed to the far end of the tube1 thus making way for the explosive mixture to reach the hot portion1 and explode1 thus sending a jet of flame into the main volume of the mixture which is immediately ignited4 ,hence there is no advantage in having a tube too long1 while1 on the other hand1 it must not be too short4 ,illustration3 ,,fig4 #ac4 ,illustration3 ,,fig4 #ad4 ,illustration3 ,,fig4 #ae4 ,the asbestos lining1 shown in fig4 #ac1 may be of various thicknesses1 according to the size of the chimney and the tube2 the reason for this will be apparent to many2 but being a most important factor in the heating of the tube1 and consequently the working of the engine1 it will be advisable to deal with this point more fully4 ,due mainly to the peculiar behaviour of iron tubes under heat and internal pressure1 it is always advisable to look to them first of all when the engine shows signs of missing fire2 and to always examine the bore of a fresh one1 and ascertain that it is perfectly clear before putting it in4 ,the adjustment of the ignition tube1 although one of the most important and necessary to be made on the whole engine1 is in itself a perfectly simple matter4 ,it must be understood that the ignition tube cannot1 with the ordinary means at our disposal1 be kept at too high a temperature2 but it must not be assumed that either the size of the flame1 or the time the flame has been alight1 is conclusive evidence that the tube is1 or ought to be1 sufficiently hot to fire the charge successfully4 ,it is an uncommon thing to hear a man exclaim--after it has been pointed out that his tube is practically cold--,why1 it's been alight for hours6 ,if such is the case with you1 reader1 you may very rightly assume that the burner is not properly adjusted1 and so does not give the right kind of flame4 ,in order to get the hottest possible flame1 the quantity of gas and air must be mixed in the right proportions4 ,a common fault is that there is too much gas allowed to flow through the nipple1 compared with the amount of air being drawn in at the air aperture1 fig4 #ac4 ,the result is1 we get a flame of great length1 but one which is not at all suited to our requirements2 and instead of giving up its heat to the tube and the asbestos lining of the chimney1 a large amount of gas we are presumably burning in the chimney is not being burnt there at all1 for1 on applying a light just above the chimney top1 a quantity of this gas we are wasting will be seen to burn with a flickering blue flame4 ,to put matters right1 it is necessary to do one of two things--either cut down the supply of gas or increase the air-supply4 ,providing the air aperture is normal1 i4e41 the same size as it was originally1 it is better to adjust the gas1 which may be done by tapping up the nipple ,n1 as indicated in the enlarged sketch1 fig4 #ad1 until just the right amount of gas can flow4 ,as a rule1 if there is too much air1 the flame will burn with a loud roaring noise1 and is liable to fire back4 ,the nipple should then be opened out with a small reamer--the tang of a small file1 ground to a long taper point1 makes an admirable tool for this purpose4 ,whether the burner is of the ordinary bunsen type1 or the ring or stove type1 the above remarks apply1 as in every case the flow of gas is governed by the size of the orifice through which it flows4 ,there is no need to use anything beyond a touch of oil when putting in a new tube1 in order to make a perfectly tight joint2 white or red lead are quite unnecessary1 and are liable to make it a troublesome matter to remove the tube on future occasions4 ,neither should undue force be applied when putting in new tubes2 it is liable to wear the thread in the firing block1 which results in a partial stoppage of the ignition hole1 as indicated in fig4 #ae4 ,this is especially the case if we happen to get hold of a tube with its screwed part slightly smaller than usual4 ,the asbestos with which the chimney is lined should be about #a_/h in4 thick1 and1 when renewing1 the same thickness should be used as originally4 ,a thicker board will reduce the annular space round the tube1 and will have a choking effect on the flame--much the same as referred to above1 when there is too much gas and not enough air4 ,a simple method of lining the chimney is to cut a block of wood to the inside dimensions of the chimney1 less #a_/d in4 in width and thickness1 then soften the asbestos cardboard by immersing in water1 and bend it round the wood1 cutting off to the required size1 i4e41 till the two edges form a neat butt joint4 ,it can be allowed to remain on the mould until dry--when it will retain its shape--or can be put into the chimney straight away1 if it is wanted for use immediately4 ,in the latter case1 however1 it will be some fifteen minutes or so before the tube will attain its working temperature4 ,asbestos linings gradually become worn and ragged1 and small flakes are apt to detach themselves and fall down into the burner1 which1 of course1 prevents the flame playing as it should around the tube4 ,in such cases it is not always necessary to fit a new lining2 if the chimney is removed1 the loose flakes shaken out and the asbestos well damped and patted down with a wooden or steel foot-rule or other suitably shaped tool1 it will be fit for another long spell of work4 ,the nickel or hecknum tubes are treated in the same manner as the iron1 but1 as we mentioned before1 are more durable1 but require more heating to get them up to a workable temperature4 ,their greater first cost is compensated to some extent by makers in some cases guaranteeing them for six months4 ,of the porcelain ignition devices1 we will deal with the double-ended tube first1 it being the more commonly used of the two in this country4 ,this form of tube is usually about #c in4 long1 #a_/b in4 diameter1 and open at both ends4 ,it may be mounted in a metal casting1 in form not unlike the small gas stoves for heating soldering irons4 ,it is heated the greater part of its length by a couple of rows of gas jets1 and is frequently surrounded by an asbestos lining4 ,the whole arrangement is in reality a tiny furnace4 ,when in position for working1 one end of the tube is open to the ignition passage leading and communicating with the combustion chamber1 while the other end is sealed1 through butting up against a metal cap or plate4 ,an asbestos washer is interposed between the tube at each end and the metal it bears against1 thus making a more or less flexible joint4 ,a thumb screw is arranged at the outside end of the tube1 by means of which pressure can be applied to clamp it up between the washers to the desired extent4 ,some care has to be exercised in adjusting this form of tube for running4 ,when heated to the working temperature it1 of course1 expands1 so that1 if tightened up too much when cold1 it is under a fairly high compression2 and when the engine is started1 and the explosion takes place1 it not infrequently bursts1 if there is not sufficient give in the washers to allow for the expansion4 ,on the other hand1 if not clamped up sufficiently tight to start with1 when the explosion occurs1 the washer at one or each end is blown out4 ,this adjustment has to be made to a nicety1 and1 although a somewhat difficult matter1 success may be attained after one or two trials4 ,it is advisable1 after a new tube has been put in1 to start up the engine gently1 i4e41 with less than the normal supply of gas1 and increase to the full amount gradually whilst running4 ,this may be done by simply opening the gas-cock on engine partially in the first place4 ,the single-ended porcelain tube is not so well known here as on the continent2 why1 we cannot say2 certainly it is preferable in every way4 ,we give a few illustrations1 showing the method of using this tube4 ,figs4 #af and #ag show the general arrangement of tube and chimney and the manner in which they are fixed to the cylinder4 ,the device consists primarily of three parts--the body or chimney ,b1 the cover ,c1 and the tube itself ,t4 ,the body is a light iron casting1 carried by a couple of studs ,,ss1 which are either screwed into the firing block ,f1 or direct into the metal of the cylinder casting if no firing-block is used2 the latter may very well be dispensed with in the smaller-sized engines4 ,the tube is made of thin porcelain1 slightly bell-mouthed at its open end1 and is mounted in a thick metal washer ,w1 as shown in fig4 #ah in section1 the joint being made with a little asbestos paper1 moistened4 ,the block ,f and the face of the body ,b 7fig4 #af7 are recessed to take the washer ,w easily1 but the depth of both recesses taken together must be about #a_/af in4 less than the thickness of the washer ,w2 thus1 when the tube is placed in position between the body ,b and the block ,f1 and the former screwed up by means of the two nuts1 as shown in the figure #af1 the effect is to clamp the washer which carries the tube1 but not the porcelain tube itself4 ,illustration3 ,,fig4 #af4 ,illustration3 ,,fig4 #ag4 ,illustration3 ,,fig4 #ah4 ,the latter is left perfectly free to expand2 and yet1 owing to its particular shape1 the pressure in the cylinder during the compression and explosion stroke only tends to make the joint between the tube and washer more secure4 ,the action of this ignition device depends upon the tube heater ,h1 which is merely a small bunsen burner1 the flame of which impinges on the tube at one particular spot1 raising it to a very high temperature--almost white heat4 ,most of my readers will know the formation of the bunsen flame4 ,it in composed of two distinct zones4 ,the inner one1 marked ,a in fig4 #ah1 is a perfectly cold part of the flame1 and appears to be a pale-blue coloured cone4 ,it is the outer zone which is the hot portion of the flame1 hence this part only must be allowed to play on the tube4 ,the tip of the blue cone ,a must be kept about #a_/d in4 below the tube1 in order to ensure the hottest part of the flame impinging precisely where the heat is required4 ,the total length of the whole flame is1 to a certain extent1 immaterial2 but1 generally speaking1 it should be adjusted so that the length of the inner cone ,a is about #a in4 or #a-a_/d in4 ,the same methods which we described in the early part of this chapter can be employed in the adjustment of this burner1 but some care should be exercised to get the correct flame length4 ,the result of allowing the cold part of the flame to impinge on the tube is observable in fig4 #ah4 ,the black spot indicated on the drawing actually appears as a black or sooty spot when looking at the tube under these conditions2 but in reality no discoloration whatever takes place1 the spot disappearing immediately the cone ,a is made shorter1 or the burner ,h lowered in the chimney ,b1 so that the tip of ,a is just below1 and does not touch the tube at all4 ,the adjustment of the length of cone ,a may be accomplished in two ways--7#a7 by keeping the supply of gas constant1 and varying the amount of air admitted at aperture ,k1 fig4 #ah2 7#b7 by keeping the supply of air constant1 and varying the amount of gas admitted through nipple ,n4 ,the first method is to be preferred when it is necessary to make any slight adjustment due to the variation of gas pressure during the day1 and may be accomplished by fitting a small sliding shield ,g1 as shown in the figs4 #af and #ag1 and moving it round so that it covers1 more or less1 the aperture ,k4 ,thus the length of cone ,a may be adjusted to a nicety in a very few seconds4 ,this shield keeps all draughts and puffs of wind from the fly-wheel away from the aperture1 and helps the flame to burn very steadily4 ,in the first place1 of course1 the flame will be regulated by opening out or tapping up the nipple ,n 7an enlarged sketch of which is given in fig4 #ad71 so that cone ,a is just about #a-a_/d in4 long when air aperture is full open2 but once this is done1 any future adjustment can be made by throttling the air-supply1 or raising or lowering the burner bodily1 the set screw keeping it in any desired position 7see fig4 #ag74 ,from the foregoing remarks it will be seen that the most noteworthy features of this form of ignition are the ease and certainty with which the tube can be fixed in a few moments2 that when the two nuts on the studs ,,ss have been tightened up there is no likelihood of the joints being blown1 for1 as we said before1 only the metal washer is clamped up1 the porcelain tube itself being as free to expand as it was before4 ,it is also at once obvious when any adjustment of the flame is necessary2 there need be no uncertainty as to whether the tube is hot enough or not4 ,,chapter ,v ,,magneto ,,ignition ,the third form of ignition we have to deal with is the electric4 ,there are a great number of different types made and used1 but for gas-engine use perhaps that known as the magneto ignition is the most satisfactory4 ,with this form1 neither accumulators1 dry batteries1 or spark coils are required1 and consequently a greater simplicity is arrived at than would otherwise be the case4 ,in fig4 #ai we show diagrammatically the ordinary form of magneto machine4 ,virtually it is a small dynamo which is fixed to the side of cylinder casting1 and is operated in the manner shortly to be described4 ,as we do not propose to enter into more than a brief explanation of why and how this apparatus generates current to produce the required spark1 perhaps a simple analogy will make matters most intelligible to any reader not well acquainted with electrical phenomena4 ,we know that when a current of electricity is flowing in a wire1 and the wire be suddenly broken1 a spark will occur at the point of breakage4 ,this fact may be observed in an ordinary electric bell when ringing2 at the tip of the contact breaker a number of tiny sparks may be seen to occur1 due to the rapid make and break of the current flowing in the circuit4 ,precisely the same action takes place in our magneto-igniter1 but1 instead of a multitude of tiny sparks1 we produce one at a time1 at definite intervals1 viz41 at the commencement of each explosion stroke4 ,illustration3 ,,fig4 #ai4 ,in the later form of magneto machines there is a soft iron sleeve between the magnet poles and the armature4 ,the former is connected to a system of levers by which a reciprocating motion is imparted to it by means of a suitably arranged cam on the side shaft4 ,it has been found that better results are obtained by causing the magnetic field to move relative to the armature winding than to move the latter through a stationary field4 ,reference to the diagrams1 figs4 #bj and #ba1 will make this clear4 ,in fig4 #ai the cam ,c is shown just on the point of allowing the lever ,l to fly back into its normal position1 due to the action of the springs comprising a dashpot ,s4 ,as the cam rotates1 it pushes the lever ,l to the left1 the sleeve 7or virtually the armature ,a7 is also rotated through a portion of a revolution comparatively slowly2 but as soon as ,l is released1 the sleeve 7or armature7 flies back again almost instantaneously and for the moment is generating a current in the same manner as would any ordinary continuous current dynamo4 ,illustration3 ,,fig4 #bj4 ,illustration3 ,,fig4 #ba4 ,at the instant the maximum current is being generated1 the circuit is broken by means of the contact breaker ,d1 fig4 #ai1 which we show in detail in fig4 #bb4 ,the latter is mounted on the end of the combustion chamber1 and consists of two parts1 ,d and ,p4 ,illustration3 ,,fig4 #bb4 ,d is an easy fit in the hole bored to receive it1 and has a mushroom valve head and seating1 as shown1 so that it moves readily when struck by the projection ,e on the rod ,r 7fig4 #ai72 but yet1 acting in the manner of a non-return valve1 it allows no gas to escape when the explosion takes place in the cylinder4 ,d is therefore in direct metallic communication with the engine frame and earth4 ,p is a fixed metal pin1 carefully insulated from all contact with the engine frame and earth4 ,to this pin one end of the armature winding is connected1 whilst the other end is connected to the engine frame4 ,thus a closed circuit is formed1 and when the current is generated it flows from one terminal of magneto through wire to pin ,p1 on to ,d1 through ,d to earth 7i4e41 engine frame71 and so back to other terminal on magneto4 ,and as the circuit is broken between ,d and ,p1 we obtain a spark1 as previously explained1 which may be timed to take place by adjusting the position of cam ,c on side shaft relatively to the position of piston4 ,it may be said that the position of the magneto-igniter is immaterial2 it will be fixed in different positions on different types of engines1 and so long as the operating mechanism is simple and effective1 i4e41 as direct as is practicable1 it works well1 and requires little attention4 ,the timing of the spark will be dealt with in the chapter on ,cams and ,valve ,settings4 ,,chapter ,,vi ,,governing ,the devices for governing the speed of the engine may be divided1 broadly speaking1 into two classes--the inertia or hit and miss governor1 and the centrifugal4 ,of the latter type we will give an instance first4 ,in figs4 #bc and #bd the governor gear is shown diagrammatically1 consisting of a couple of weights ,,ww suspended from a vertical spindle4 ,these fly apart when caused to revolve by the bevel wheel gearing ,,bb1 and raise the sleeve ,s to a greater or lesser extent4 ,a recess in the latter engages a lever arm ,l1 through which the vertical movement of the sleeve ,s is converted into a horizontal movement of the sleeve ,t4 ,the latter is carried by the valve lever ,p1 and is virtually a roller which engages with one or other of the steps of the cam ,c1 according to the speed of the engine4 ,the object of this arrangement is to keep the ratio of air to gas uniform throughout all variations of load4 ,the gas and air valve are shown as both being operated by the same lever ,p1 the accurate timing of the latter being obtained by means of set screws4 ,illustration3 ,,fig4 #bc4 ,illustration3 ,,fig4 #bd4 ,messrs ,dougill ,co4's engines are fitted with a step down cam and governor such as this4 ,the centrifugal governor is often arranged so that instead of the charge being merely reduced in volume1 the whole charge is cut out1 and no explosion whatever takes place4 7,in this respect the same results are obtained as when a hit and miss governor is used1 and the latter form therefore is to be preferred1 especially on small engines1 where the difference between the indicated power and the brake power is always1 even under the best conditions1 fairly great47 ,in this case the governor lever only operates the gas valve2 the air valve being opened on every charging or suction stroke1 whether gas is admitted or not4 ,another application of the centrifugal governor is to suspend a distance piece on the end of the governor lever1 so that at normal speed this distance piece is interposed between the gas valve spindle and the lever operating it4 ,in that case the gas valve will be opened4 ,but if the speed is above the normal1 the distance piece will be raised clear of the valve spindle1 and the opening mechanism 7driven by a cam on the side shaft7 will simply move forward and recede again without ever touching the gas valve4 ,there are any number of movements which have been1 and there are many more which could be1 devised to give the same result2 and it depends principally upon the form of engine in question which device we adopt4 ,the simplest and most direct action is1 however1 always the best2 complicated mechanism is to be deprecated1 especially on small engines4 ,for this reason is the inertia governor more generally fitted to such engines4 ,illustration3 ,,fig4 #be4 ,a simple form of this governor is shown in fig4 #be4 ,the gas valve ,v is shown on its seating4 ,it is screwed into a pecker block ,b1 and pinned as shown4 ,the latter should be of cast steel1 tempered to a straw colour2 or if mild steel or iron is used1 it must be well case-hardened1 in order to resist wear4 ,the pecker ,p 7also tempered hard7 is mounted on the cast-iron weight ,w1 which in turn is pivoted on the valve lever ,l4 ,it will be seen that the weight ,w 7which is only held in the position shown by the spring ,s7 will tend to lag behind when a sudden upward motion is imparted to the lever ,l4 ,thus it depends upon the degree of suddenness with which ,l moves whether the pecker ,p remains in the same relative position to the lever as the latter travels upwards and engages with the pecker block ,b1 or whether it misses it and simply slides over the face of the block4 ,the adjustment of the spring ,s is effected by screwing up or slacking out the milled nuts ,t2 and on the degree to which this spring is compressed depends the sensitiveness of the governor1 and consequently the speed of the engine4 ,to obtain accurate and steady governing with this type of mechanism it is essential that the weight be perfectly free on its spindle1 and that nothing but the spring ,s holds1 or tends to hold1 it in the position shown4 ,on this account it is advisable to provide a lip on the pecker block1 as shown1 to keep the area of contact as small as possible4 ,this effectually prevents any sticking1 should a superfluity of oil happen to get on either block or pecker4 ,for similar reasons there should be some clearance between ,a and the pecker1 i4e41 the latter should only bear at one point and not bed flat against ,a4 ,another form of inertia governor is shown in fig4 #bf of the hit and miss type1 which is employed by ,messrs ,capel ,co4 on many of their engines4 ,it consists of three main parts--the brass arm ,l carried on a stud ,d1 on which it is free to move2 the weight ,w1 which carries the pecker ,p pivoted at the upper end of ,l2 and the pecker block ,b1 which engages the pecker when the engine requires a charge of gas4 ,the governing action is dependent upon the shape of the operating cam from ,x to ,y4 7,in the case already dealt with1 the lever ,l serves to operate both air and gas valves1 and so one cam only is necessary2 but in this instance the gas valve is operated by a separate cam1 and a greater nicety of adjustment is obtainable47 ,illustration3 ,,fig4 #bf4 ,if the speed of the engine is sufficiently high1 the arm ,l is thrust forward at such a rate that the weight ,w tends to lag behind1 with the result that ,p is raised above the notch in ,b1 as shown by the dotted lines in drawing4 ,on the other hand1 when the speed is too low1 the arm ,l will not be thrust forward with so great a degree of suddenness1 the weight ,w will have time to move with ,l1 and the relative position of ,w and ,p to ,l will remain the same4 ,hence1 in the first case1 when a further forward movement is given to ,l by the cam1 the pecker ,p is clear of ,b1 and omits to open the gas valve ,v2 in the second case1 ,p engages with ,b1 and the gas valve is held open during the time the portion of cam ,y to ,z is passing over the roller ,r on arm ,l4 ,the great drawback to some forms of governors is not that they fail to govern well when new1 but that no provision is made to ensure them working steadily when a bit worn4 ,the shape of the cam has everything to do with the regular working of this form of governor4 ,supposing our cam was of the shape shown in fig4 #bg1 i4e41 the governing and opening portion all in one curve1 it would cause the pecker to move both forward and in an upward direction at the same time1 so that at the moment of engaging ,b1 ,p might still be moving in an upward direction1 which would cause uncertainty of action1 especially if the tips of the engaging members were at all blunt through wear2 and1 in all probability1 ,p would fly off ,b after partially opening the gas valve4 ,this behaviour is very undesirable1 as the small quantity of gas so admitted to the cylinder is quite useless1 and a sheer waste is incurred4 ,with the governing arrangement shown in fig4 #bf1 this trouble does not exist4 ,the cam is so designed that the first rise from ,x to ,a determines whether or not the valve is to be opened2 the curve from ,a to ,y is struck from the centre of the side shaft2 thus1 during that portion of the revolution the arm ,l is stationary1 and the pecker at the same instant takes up a definite position either in the notch in ,b or on top of it1 and is ready to open the valve if the speed of the engine is such as to require an explosion1 or simply to slide over the top of ,b1 allowing the valve to remain closed4 ,it is most interesting to observe the action of this governor2 when an engine fitted with one is running very slowly1 the three distinct movements of the pecker ,p may be clearly discerned as the respective portions of the cam pass over the small roller ,r4 ,illustration3 ,,fig4 #bg4 ,,chapter ,,vii ,,cams ,,and ,,valve ,,settings ,with the gas1 as with any other kind of engine1 the valve settings are of primary importance4 ,on very small engines it is often the case that only the exhaust valve is operated mechanically4 ,again1 there are several well-known makes which operate the gas and exhaust mechanically while the air valve is opened by suction alone4 ,though opinions differ as to which is the best course to take1 there can be little doubt that1 with all three valves mechanically operated1 a greater nicety of adjustment is obtainable than would be otherwise possible4 ,and provided the working parts are neatly made and finished1 they will take but little power to drive them2 and such loss would be compensated by the additional power and efficiency obtained from the engine1 due to satisfactory and correct adjustment4 ,in fig4 #bh we give a diagram showing the exact positions of the crank when the gas1 air1 and exhaust valves open and close respectively1 under normal conditions of working4 ,the solid circle represents the first revolution of the crank shaft1 starting from the commencement of the suction stroke1 and the dotted circle the second revolution1 during which the explosion and exhaust strokes take place2 the dotted horizontal line shows the position of crank at the back and front dead centres4 ,as a clear conception of why certain things happen under certain conditions is most desirable1 we will first describe the operation of marking off the cams which operate the respective valve levers1 and then discuss the effect of various settings of the valves on the running of the engine4 ,illustration3 ,,fig4 #bh4 ,assuming that we are still dealing with the ,otto cycle engine1 the cam or side shaft will revolve at precisely half the speed of the crank shaft4 ,this #b to #a motion is obtained by means of toothed wheels1 or a screw gear4 ,in the former case1 where plain or bevel cog-wheels are employed1 the one fixed on the crank shaft must be exactly half the diameter of the one on the side shaft1 i4e41 it must have one half the number of teeth4 ,on the other hand1 if a screw gear is used1 the relative diameters of the two wheels may vary1 but the pitch of the teeth on the one must be twice that of the other4 ,these wheels sometimes have the teeth or thread formed in the casting1 and sometimes they are cut after a plain casting has been made4 ,the latter kind are1 needless to say1 better than the former1 which often require filing up in order to make every tooth alike1 and ensure sweet running4 ,we know already in what positions our crank has to be at the opening and closing of the three valves1 and with the aid of the diagram1 fig4 #bh1 we can determine the size of the cams4 ,in fig4 #bi1 ,s is the side shaft to which the cams have to be keyed1 ,r the roller on valve lever1 the latter being represented by the centre lines ,,ll1 as all we require to find is the motion this lever will transmit to the valve1 the spindle of which is shown at ,v4 ,fig4 #cj shows diagrammatically the position of crank at the opening and closing of the air valve4 ,from this we see that the angle through which the crank travels during the time the air valve is open is equal to the obtuse angle ,,abc4 ,now1 as the side shaft ,s revolves at half the speed of crank1 it is obvious that the former will travel through only half that angle in the same space of time1 i4e41 through an angle equal to ,,abd4 ,we can now transfer this angle on to ,s1 fig4 #bi1 and draw two lines ,,se1 ,,sf1 cutting a circle ,,ghj1 representing the back of the cam1 which latter passes in front of the roller ,r without causing any movement of the lever ,l4 ,illustration3 ,,fig4 #bi4 ,illustration3 ,,fig4 #cj4 ,illustration3 ,,fig4 #ca4 ,it will be seen that by drawing a line forming a tangent to the circle ,,ghj at ,f and another at ,e1 and producing these1 they will meet at point ,k4 ,consequently1 as the side shaft rotates in the direction indicated1 the lever ,l will begin to open the valve ,v when the cam is in the position shown in fig4 #bi1 reach a maximum opening at ,k1 and finally close when the cam has moved so that point ,e is now where ,f was4 ,with a cam of this shape1 however1 a considerable portion of the stroke would have passed before the valve was raised any appreciable distance off its seat2 it would only be fully open for an instant1 viz41 when ,k was passing over ,r1 and would begin to close again directly4 ,moreover1 if the engine were running at even a slow speed1 the motion imparted to lever ,l would be indefinite2 and this1 especially if the governor is fitted to the air valve lever1 as in fig4 #be1 is very undesirable4 ,therefore1 to obtain a definite opening we must set out the cam1 as shown in fig4 #ca4 ,in this diagram the roller is shown standing clear of the back of cam by about #a_/af in4 ,a line ,,mn is then drawn1 forming a tangent to both roller ,r and circle ,,ghj at points ,f and ,o respectively4 ,this gives us the opening portion of cam4 ,then from the centre ,s with radius ,,sf describe the arc ,,fe 7shown dotted in fig4 #ca71 and set off the angle required 7,,abd1 fig4 #cj71 as previously explained4 ,through point ,e draw a line forming a tangent to circle ,,ghj1 and produce it towards ,p4 ,this line gives us the closing portion of cam4 ,the distance ,w is of course variable1 according to the amount of lift we give the valve4 ,by comparing these two diagrams it will be seen that in both cases the valve will be opened the same length of time1 but in first case the motion will be indefinite and uncertain4 ,in practice the corners are rounded off somewhat1 in order to obtain a steady motion2 and when the air cam is also the governing cam1 it is advisable to round off the opening face1 as indicated in fig4 #cb4 ,upon the shape of this face both the sensitiveness and the life of the governor gear depends4 ,if it is nicely rounded off1 giving a gradual rise1 very little tension 7or compression1 as the case may be7 of the controlling spring will be necessary to give the required speed to engine2 whereas1 if the rise is sudden1 the spring will have to be screwed up tighter1 and1 if uneven and lumpy 7i4e41 not a fair curve71 the result will1 of course1 be erratic governing4 ,illustration3 ,,fig4 #cb4 ,a certain amount of clearance should always be provided between the roller and the back of cam 7compare figs4 #bi and #ca71 that is1 the roller should not bear against the cam1 except during that portion of the stroke in which it is actually operating the valve1 viz41 from ,f to ,e 7fig4 #ca74 ,a small stop interposed between the lever and some convenient part of the engine1 such as the side-shaft bracket bearing1 answers this purpose4 ,illustration3 ,,fig4 #cc4 ,illustration3 ,,fig4 #cd4 ,the size and shape of the exhaust cam is found in the same manner as above described2 the angle through which it operates is greater than that of the air cam1 and is shown in fig4 #cc4 ,a fair margin should be allowed for filing or machining these castings up2 the shape and sizes arrived at by the above described method being finished measurements4 ,fig4 #cd gives the outline of an exhaust cam worked out from the setting diagram1 fig4 #cc4 ,illustration3 ,,fig4 #ce4 ,illustration3 ,,fig4 #cg4 ,illustration3 ,,fig4 #da4 ,illustration3 ,,fig4 #db4 ,we may now consider the relative positions these two cams will occupy when keyed up on the side shaft4 ,assuming that we have both cams finished to the proper shape and size1 and the keyway cut in the side shaft1 we can commence to mark off the position of keyway in the air cam4 ,with the crank in the position shown in fig4 #ce1 the air cam is slipped on to the side shaft and brought to the position shown in fig4 #cb4 ,the keyway being already cut in the side shaft1 the position for that in the cam may be scribed off1 as shown by dotted lines 7fig4 #cb71 the cam removed1 and the keyway cut4 ,it is as well1 however1 to check this mark by turning the crank round to position shown in fig4 #cg1 i4e41 the closing of air valve4 ,the side shaft will also turn through exactly half this angle1 so that when the cam is again slipped on the latter1 the scriber marks and keyway in shaft should be exactly in line1 as they were in fig4 #cb1 and the fall of the cam--the closing portion--should just be touching roller ,r1 but not sufficient to keep the valve open 7see fig4 #ch74 ,the slightest movement of the crank from this point in a forward direction should result in a little play being felt in the lever ,l1 assuming that the cam is also moved just enough to keep the scriber marks in line with the existing keyway4 ,illustration3 ,,fig4 #cf4 ,illustration3 ,,fig4 #ch4 ,illustration3 ,,fig4 #ci4 ,by these operations it will be at once evident whether the cam is too large or too small4 ,supposing it is too small1 we will obtain two sets of marks indicating the position of keyway1 as shown in fig4 #ci1 and it is obvious that we must give the lever less play by screwing up the set screws shown in fig4 #aa4 ,the effect of this is to cause the valve to open earlier and close later than it would if the play were greater2 as it would were the operating portion of cam larger4 ,a minimum amount of play must always be allowed1 however4 ,when two sets of marks are obtained1 the mean must be taken and the keyway cut as shown by the thick lines in fig4 #ci4 ,the exhaust cam in larger engines is usually made with a swelling on the opening portion1 as shown in fig4 #dj1 so that the valve is very slightly opened some time before the crank has reached the position shown in fig4 #da4 ,fig4 #db shows position of crank at the close of exhaust valve1 and the two last-mentioned diagrams correspond with the two positions in which the exhaust cam is shown in fig4 #cd4 ,the small lump on the back of exhaust cam1 fig4 #dj1 is only required on engines above #c ,b4,h4,p4 to relieve the compression on the compression stroke when starting up4 ,by moving the roller ,r on valve lever longitudinally1 so that it engages both parts of cam as they pass in front of it1 the exhaust valve is held open during a small portion of the compression stroke1 usually closing when the crank has reached the bottom centre4 ,referring again to fig4 #bf1 this gas or governor cam may be set out1 and the keyway marked on the same principle as already described for the air and exhaust valves4 ,an end view of the three cams keyed up on the side shaft is given in fig4 #dj;,a4 ,in small engines it is convenient to have the air and exhaust cams made in one casting1 when one key only will be required4 ,on some engines1 instead of employing a movable roller or valve lever1 the exhaust cam is fitted on side shaft with a feather--i4e41 a headless key--and the cam being capable of longitudinal movement1 such movement being controlled by a small lever or handle1 called the half-compression lever4 ,illustration3 ,,fig4 #dj4 ,illustration3 ,,fig4 #dj;,a4 ,having once thoroughly grasped the important part the cams play in the working of the engine1 it will be an easy matter to adjust the valve settings1 and to keep them adjusted correctly4 ,the effect of a wrong setting will then be strikingly apparent4 ,on small engines a separate cam to operate the gas valve is not a necessity2 and the practice of fitting the gas valve spindle 7or the pecker1 the effect would be the same7 with a device for increasing or diminishing its length1 is also unnecessary and unsound4 ,the wear on a well-designed gas valve operating mechanism is practically nil2 and even if there was wear1 the effect would be to cause the valve to open a trifle later and close sooner than it would otherwise1 i4e41 it would remain open a shorter time during each charging stroke4 ,this in turn 7other conditions remaining the same7 would give us a weaker mixture2 and although too weak a mixture is preferable to a too rich one1 we should have to adopt some means of increasing the richness of the mixture2 otherwise the maximum power of the engine would soon be seen to diminish4 ,to get the mixture normal again we must either enlarge the gas inlet or cut down the air-supply somewhat1 and so keep the proportions the same4 ,that is to say1 the quality of the mixture is dependent upon the relative dimension of the gas and air inlets4 ,we know by actual trial that if at the completion of the charging stroke the pressure in the cylinder is approximately that of the atmosphere1 better results are obtained than when the pressure is considerably below that of the atmosphere4 ,thus1 the larger we make the inlet ports 7but still retaining correct relative dimensions7 the more readily will the mixture be drawn into the cylinder as the piston moves forward1 tending to create a vacuum4 ,of the two courses open to us to retain a good mixture it is preferable to open out the gas-supply1 for by cutting down the air-supply1 and sucking the gas in1 due to the partial vacuum being formed1 we should be keeping the proportions correct at the expense of reducing the total volume of the explosive mixture 7more strictly speaking1 the density of the charge7 admitted to the cylinder4 ,under normal conditions it is not necessary to create a high vacuum to suck the gas into the cylinder1 but it is as well to understand what results we would tend to produce1 did we work on these lines4 ,of course1 with small high-speed engines fitted with suction air valve1 the vacuum is higher than it would be in slow-speed engines with mechanically operated valves4 ,if we take an extreme case as an example1 where1 to get any gas to speak of into the cylinder the air-supply would have to be cut down or throttled to an abnormal extent1 we will realise at once that such a small quantity of both air and gas would have been drawn in1 and consequently the mixture would be so rarefied that on the compression stroke the pressure would possibly be extremely low and totally inadequate to produce efficient working4 ,moreover1 working at such a high vacuum as this would not only prevent us obtaining a normal explosion in the cylinder1 but would upset the working of the exhaust valve4 ,the latter being held down on its seat during the suction stroke by means of a spiral spring would be lifted off its seat by suction 7the partial vacuum in the cylinder71 and any burnt gases which happened to be hanging about in the exhaust port or pipe would be drawn into the cylinder again1 and tend to damp the ensuing explosion4 ,too early closing of the exhaust should be avoided almost as rigorously as too late4 ,the latter will affect the working in a similar way to the exhaust being lifted on the charging stroke by suction2 on the other hand1 if it closes too soon1 the entire volume of burnt gases will not have been swept out of the cylinder1 and the effect will again be to damp the following explosion4 ,the gas valve opens just after the crank is above the back centre and closes just before the front centre is reached1 that is1 opening a little after the air valve and closing a shade before it1 thus every particle of gas is used in the cylinder1 due to a draught of air being drawn in after the gas valve has been closed4 ,the settings of the valve being of primary importance1 no matter what size engine we are dealing with1 and being also the most confusing matter for anyone unacquainted with gas engines to grasp1 it will not be out of place to suggest a simple method of checking these settings4 ,let us begin by pulling the fly-wheel round backwards until we feel the piston is on the compression stroke1 then from this point--the crank being about #de deg4 above the front centre--pull the wheel round until the crank is in the position for the exhaust opening 7see fig4 #bh74 ,in this position there should be but the slightest play in the exhaust lever1 showing that the valve is just on point of opening2 and by keeping one's hand on the lever whilst the fly-wheel is pulled round very slowly 7it is a good plan to get some one else to do the pulling round71 it is possible to ascertain the precise point at which the valve opens4 ,next pull round till the crank is in the position for the air valve opening1 and observe that it is set correctly4 ,then go on to a trifle above the back centre1 where the exhaust valve should close1 and so on till the opening and closing of each valve has been checked4 ,it will be noticed that the air1 and sometimes the gas1 valve opens before the exhaust closes4 ,this overlap is necessary2 and it will be found that the smaller the engine and the higher the speed the greater this overlap will be to obtain good results1 although a good deal of individual judgment must be used in settling the exact amount of overlap1 as the requisite amount may1 to get the best results1 vary in different engines of precisely the same dimensions and type4 ,when dealing with engines which have no separate gas valve--the gas being admitted with the air1 which is sometimes the case with very small engines--the above notes referring to the gas setting independently1 will1 of course1 not hold good4 ,it may be mentioned with regard to the lump on the opening side of the exhaust cam1 that this if overdone is found to be detrimental on large engines1 and even on small ones4 ,if it is too large1 it will cause both exhaust valve and seat to become burnt and pitted1 due to the surface being exposed to the exceedingly high temperature of the expanding gases4 ,if it is too large1 it is equivalent to opening the exhaust valve too early1 and the effect is the same1 viz41 a waste of power and damage to the valve and its seat4 ,illustration3 ,,fig4 #dc4 ,illustration3 ,,fig4 #dd4--;,brake ,testing4 ,the method of grinding in the valves to their seats with emery powder and oil is so well known that no further description is needed here4 ,we give1 however1 in fig4 #dc a sketch showing a very expeditious way of dealing with very badly worn or burnt seats4 ,the sketch explains itself4 ,such a tool is readily made2 even the cutter could be turned and filed up to shape and then hardened at home4 ,by lightly tapping in the taper cotter pin little by little1 sufficient pressure is put on the cutter to make it an easy matter to completely re-face an old seat or form a new one4 ,a ,t-wrench or tommy can be used to work the cutter spindle4 ,the lower part of the latter must be the same diameter as the existing valve spindle2 the bush acts as a guide2 and as the bevel of the cutter should be the same as that of the valve1 a very little grinding in with emery powder is required to finish the job off4 ,in fig4 #dd we give a diagram showing the method of testing for ,brake ,h4,p4 of engine1 as it is frequently interesting to make such a simple test after any alterations or adjustments have been made4 ,two spring balances and a rope or cord 7according to the size of the engine71 fitted with a few wood blocks as shown in section1 fig4 #dd1 to keep the rope on the rim of fly-wheel1 is all that is required for this test4 ,the following formula may be used for arriving at the ,b4,h4,p43-- ,b4,h4,p4 7,s#a - ,s#b7 #c4ad x ,d x ,r _/ #ccjjj ,s#a ,reading in lbs4 of spring balance ,no4 #a4 ,s#b ,reading in lbs4 of spring balance ,no4 #b4 ,d ,diameter of fly-wheel and diameter of brake rope in feet4 ,r ,revolutions of fly-wheel per minute4 ,as #c4ad x ,d _/ #ccjjj will always remain the same for any given engine and gear1 we may call that expression ,c2 then the ,b4,h4,p4 may be written-- ,b4,h4,p4 7,s#a - ,s#b7 ,c ,r ,,chapter ,,viii ,,oil ,,engines ,the small oil engine is practically the same as the gas engine1 with the addition of a vaporiser for converting the oil into gas1 or vapour1 to be exploded in the cylinder2 consequently the one may be converted into the other in many cases without much trouble4 ,the difficulty of producing an efficient oil engine lies principally in devising a satisfactory and reliable vapouriser--one which will work equally well under all loads4 ,the heat supplied to the chamber must be sufficient to vaporise the oil1 but not great enough to decompose it4 ,there are various methods of vaporising the oil1 and many types of vaporisers are employed to attain the same end4 ,there are some in which a charge of oil is drawn by suction into a hot chamber in which it is converted into vapour and at the same time mixed with a small quantity of hot air2 this rich mixture is then passed into the combustion chamber of the engine1 in the same manner as coal-gas would be1 where it is further diluted with more air drawn in through the air valve4 ,other arrangements cause a jet of oil to be injected into a chamber containing hot air1 in the form of spray1 which immediately converts the oil into vapour1 and is then passed into the cylinder1 compressed1 and fired4 ,then1 again1 we can pump oil through a spraying nipple into the vapouriser 7which is kept at a suitable temperature7 whilst the cylinder is being filled with air on the suction stroke4 ,on the following compression stroke the air is driven into the vapouriser1 which communicates with the cylinder through a narrow neck1 and mixes intimately with the oil vapour4 ,gradually1 as the pressure rises1 due to compression1 the charge becomes more and more explosive1 until at the completion of this stroke it has attained the proper proportions of air and oil vapour1 and is fired by the temperature of the vapouriser and that caused by a high compression2 that is1 the charge is fired automatically2 and once the engine is running1 no heating lamp is required to keep the vapouriser at the correct temperature4 ,it is necessary1 however1 to raise it to the workable temperature at starting4 ,this is known as the ,hornsby-,akroyd method4 ,capel's arrangement is also simple and efficient1 and has the additional advantage of being capable of being fitted to their existing gas engines1 the conversion being made in a very short time4 ,this vapouriser consists primarily of a tubular casting ,a1 on the outside of which are formed a series of vertical ribs1 shown in plan1 fig4 #df1 running to within a short distance of the flange at one end1 as shown in the section1 fig4 #de1 thus providing an annular space ,c between the upper ends of the ribs and the flange4 ,this casting is enclosed by an outer casing ,b1 which fits well over the inner tube4 ,it has also a number of small holes drilled near the lower end communicating with the channels between the ribs4 ,thus it will be seen that when the gas valve is opened and suction takes place1 air is drawn in through these holes1 passes up into the annular space ,c below the top flange1 from there travels to the opposite side of vapouriser1 and mixes with the oil which is also being drawn in through a small nipper at ,n1 fig4 #de4 ,both then pass between a series of pegs1 where they become thoroughly mixed1 and finally pass on to the inlet valve ,v1 fig4 #dg1 and so into the cylinder1 where the complete charge is mixed up and compressed and fired in the usual manner4 ,iron ignition tubes may be used1 and one heating lamp serves a double purpose in keeping the tube and vapouriser hot at the same time4 ,this lamp is fed by means of a pump actuated from the side shaft4 ,the plunger of the pump is loaded with a spiral spring1 which may be adjusted to give any desired pressure1 and is kept constant and steady by means of an air vessel4 ,this pump is shown in fig4 #dh4 ,it is actuated by means of a rod and lever from the side shaft of engine4 ,the plunger ,p works in a barrel ,b1 which is carried by a small reservoir ,r1 the latter being in communication with the main oil tank by means of the pipe ,h4 ,illustration3 ,,fig4 #df4 ,illustration3 ,,fig4 #de4 ,illustration3 ,,fig4 #dg4 ,illustration3 ,,fig4 #dh4 ,illustration3 ,,fig4 #di4 ,illustration3 ,,fig4 #ej4 ,illustration3 ,,fig4 #ea4 ,the plunger is loaded with a spiral spring1 and has a ball valve1 as shown4 ,intermediate between this small reservoir and the main oil tank is another set of valves1 shown in fig4 #di4 ,it will be seen that the suction of the pump will draw the oil up1 the small and lower ball valve1 of course1 allowing it to pass freely4 ,on the down stroke the lower valve will be automatically closed1 and the oil will be put under pressure1 this being determined by the load on the plunger valve1 which is adjustable by means of the screw ,s1 fig4 #dh4 ,when the required pressure in the pipe ,p1 figs4 #de and #di1 has been attained1 the plunger valve lifts on each stroke and the surplus oil flows through the plunger into the small reservoir ,r4 ,the latter is at about the same level as another still smaller reservoir ,m 7shown in figs4 #dg and #ej71 a flow of oil being established between the two by means of a pipe ,q 7see figs4 #dh and #ej74 ,in the reservoir ,r is fitted an overflow pipe1 so that the oil cannot rise beyond a certain level2 hence the head of oil in the smaller one ,m is always constant4 ,on the suction stroke a partial vacuum is formed in the engine cylinder1 consequently the pressure in the vapouriser drops somewhat below that of the atmosphere1 and this small difference in pressure is enough to cause the oil to rise in the small passage ,x1 fig4 #de1 beyond its normal level1 and overflow into the vapourising chamber1 as previously described4 ,the valve or nipper ,n is shown open in the diagram1 fig4 #de1 and all that is required to stop the engine when running is to drop the small handle ,l1 fig4 #de1 when the valve will close1 due to the spring ,s4 ,the air vessel shown in fig4 #di is in communication with the pipe leading to the blow lamp4 ,a pressure gauge can also be fitted1 although it is not in any way a necessity4 ,the ratchet wheel and pawl shown in fig4 #dh are part of the lubricator4 ,the wheel drives a brass or gun-metal plug1 producing an intermittent rotary motion4 ,the plug has a small hole in its periphery1 which becomes filled with oil when it is at the upper part of its travel1 and empties the oil out into a discharge pipe ,t1 when it is inverted1 and is then led away and applied to the piston at the required spot4 ,fig4 #ea shows this arrangement in section4