ROI 



;i end of the cylinder when the engine is on dead 

 center. 



Q. Is there any rule for giving an engine the proper 

 lead? 



A. No. 



Q. Why not? 



A. Owing to their variation in construct inn, speed. 

 etc. 



Q. What would you consider the proper amount of 

 lead, generally? 



A. From & to ^ of an inch. 



Q. What is lap? 



A. It is the distance the valve overlaps the steam 

 ports when in mid position. 



Q. What is lap for? 



A. In order that the steam may be worked expan- 

 ly. 



Q. When does expansion occur in a cylinder? 



A. During the time between which the port closes 

 and the point at which the exhaust opens. 



Q. What would be the effect on an engine if the 

 exhaust opened too soon? 



A. It would greatly lessen the power of the engine. 



Q. What effect would too much lead have? 



A. It would also weaken the engine, as the steam 

 would enter before the piston had reached the end of 



