ENGINES, MOTORS AND TRACTORS 



745 



at present are of the four-cycle type; also all but a few of the automobile 

 engines are of this type. By experience, users and manufacturers have 

 found the four-cycle engine the most successful. 



Vertical and Horizontal Engines. — Either four-cycle or two-cycle 

 engines may be vertical or horizontal in appearance. The horizontal 

 engine, especially of the four-cycle type, is much easier to repair than the 

 vertical one. However, the vertical engine requires less space for its 

 installation, but may not lubricate as well as the horizontal engine with the 

 oil flowing from the top of the cylinder. 



Ignition. — There are three types of ignition used in gas engine opera- 

 tion: high tension, low tension and compression ignition. 



UEL PUMP OPERATiNivJ POO 



FUEL PUMP LEVf.S 



GOVERNOR SHAFT 



iOVfRNOR VOKt 



Sectional View of a Four-Cycle Horizontal Gas Engine. 1 



The high tension system requires a current of electricity with a voltage 

 sufficiently high to cause a spark to jump from one point to another of a 

 spark plug. This system is used, as a general rule, on high-speed motors. 



The low tension system requires a low voltage for ignition of com- 

 pressed air and gas mixed together in the compression chamber. The spark 

 is produced by the separation of two points in the cylinder which have been 

 brought together and caused to separate. 



The source of current for these two types of electric ignition may be 

 from dry or wet batteries or from magnetos. A very successful means of 

 ignition is the battery to start the engine and the magneto to furnish the 

 source of current after it is in operation. In no case should any one pur- 

 chase a modern engine without a magneto. It is not heir to the many 



1 Courtesy of Fairbanks, Morse & Co., Chicago, 111. 



