FARM MOTORS 



353 



trouble is not serious, the rings may be loosened by feeding in 

 kerosene through the lubricator. When the rings become 

 worn, they should be replaced. 



Leaks may^ also take place past the valves. Often 

 charred oil will* lodge on the valve seat, preventing it from 



Fig. 224. A sectional view of a gas engine cylinder, showing 

 the cylinder volume and clearance space. 



closing tightly. Cleaning will often overcome this difficulty; 

 but when scored or pitted, the valve must be ground on its 

 seat with emery and oil until a perfect fit is again secured. 



QUESTIONS 



1. What are the four fundamental essentials of gas engine 

 operation? 



2. What is meant by an explosive mixtine? 



3. What are some of the difficulties encountered in obtaining an 

 explosive mixture? 



4. What are the indications of a rich mixture? A lean mixture? 



5. Explain how the quality of the mixture may be tested. 



6. How does compression influence the power of an engine? 



7. What are the common causes for the loss of compression? 



