THE VALVE-GEAR gy 



Let us add that in nine cases out of ten, where an expert 

 is called to reset a valve, he finds that it has been disturbed 

 since it left the testing room. Do not, then, conclude that 

 your valve is "off," until you have carefully investigated 

 whatever trouble there may be. 



There are men in nearly every locality throughout 

 the country, who are confident that they themselves know 

 more about setting valves than do the manufacturers. These 

 men affirm that whatever trouble they may have is due 

 to the working of the valve, and, when no improvement 

 is shown after they have reset it, they say that the valve- 

 gear was not properly constructed and designed originally. 

 If they had carefully investigated the trouble before dis- 

 turbing the valve, they would have discovered the real 

 cause, due probably to either insufficient cylinder and valve 

 lubrication, or to a priming tendency of the boiler. The 

 causes of, and the remedies for these difficulties are dis- 

 cussed elsewhere in this book. 



Finding the "Dead Centers." An engine is on its 

 "dead center" when a line drawn through the center of 

 the piston-rod will pass through the center of the crank- 

 pin. There are two, the "crank" dead-center, when the 

 piston is at the end of the cylinder nearest the crank-shaft, 

 and the "head" dead-center, when the piston is at the or> 

 posite end. An engine is said to be running "over" when 

 the top of rim of fly-wheel runs away from the cylinder 

 and running "under" when the top of rim of fly-wheel runs 



