856 AGRICULTURAL ENGINEERING 



primarily in providing a source of electricity and suitable 

 mechanism to bring the points together at the proper time 

 and to separate them at the proper time for the sparks so pro- 

 duced to fire the mixture in the cylinder. 



The make-and-break system does not use high-tension or 

 high-voltage electricity. Voltage corresponds to pressure, 

 or ability of the electricity to overcome resistance. For this 

 reason the make-and-break system does not require such 

 careful insulation as does the high-tension system. There 

 are, however, the moving parts inside of the cylinder, and 

 the mechanism operating it is such that it is not convenient 

 to make provision for varying the time of ignition. Failure 

 on the part of the make-and-break system may be generally 

 traced to failure in the source of current, or to a break-down 

 of insulation. There are many other minor causes of failure, 

 but space does not permit a discussion of them here. 



Testing the Make-and-Break System. When an engine 

 fails to start, a test should be made of the ignition system. 

 This is generally done by making and break- 

 m ^ ^ e circuit by hand outside of the engine 

 cylinder, and judgment is then passed upon 

 the size of the spark as to whether or not 

 it is sufficient to ignite the charge. After 



Fig. 226. A . , . . 



n d-break the insulation on the wires becomes worn 



and damaged, there may be an escape of 

 electricity without passing through the igniter points. The 

 igniter points may become covered with scale, oil, or dirt 

 which will prevent the electricity from passing from one to 

 the other when desired. Often the movable points fail to 

 work freely, owing to lack of oil, preventing the sharp, quick 

 separation of the points, which is quite necessary to secure a 

 good, iat spark. 



