428 FARM MOTORS 



570. Lubrication. Lubrication of the gas engine cylin- 

 der is very important. A special oil must be used 

 to stand the high temperature met with in gas-engine 

 practice. Any oil containing animal fat will not work at 

 all because when subjected to high temperature it will 

 decompose and be reduced to a charred mass. First-class 

 steam engine cylinder oil will not give good results be- 

 cause it contains certain elements which will carburet 

 like gasoline under high pressure and high temperature. 

 Good engine oil is satisfactory for other parts. 



571. Gasoline engine troubles. The gasoline engine is 

 often condemned as being unreliable. This may be ex- 

 plained from the fact that unless conditions are just right 

 the gasoline engine will stop or refuse to work at all. 

 This is different in other forms of motors because very 

 often the thing which interferes with its operation comes 

 on gradually and may not be noticed by the man in 

 charge. It has been stated that "there are four things 

 essential to the operation of a gasoline engine," namely : 

 compression, ignition, carburetion or proper mixture, and 

 proper valve action. If these four conditions are ob- 

 tained, the engine will work or run. If there is failure 

 to obtain any one of them, the engine will refuse to run. 

 Often an engine will stop, and it is difficult to tell which 

 one of the various conditions is wrong. It is necessary 

 to trace the trouble and correct it. 



572. Compression. It is easy to detect whether or not 

 there is compression by turning the engine over ; if a 

 charge of air is caught and compressed, this is an easy 

 matter to determine. Failure to get compression may be 

 due to a valve refusing to seat or to a leak past the valve. 

 It may also be due to a leak past the piston, to broken 

 piston rings, poorly seated rings, or rings gummed with 

 oil. If valves do not seat correctly, it may be due to 



