GAS ENGINES 



5*5 



valve is one that opens in the direction of its length. The 

 rotary valve has been used to a very limited extent. Trouble 

 is encountered in properly cooling and lubricating this type 

 of valve. The slide valve, as used in a steam engine, has 

 been modified for gas-engine use and is known as the sleeve 

 valve. This mechanism uses two cast-iron sleeves which 

 move up and down immediately outside the piston. The 

 sleeves have holes or ports which are so placed that they 

 register at the desired piston positions. Valves are placed 

 vertically, horizontally, and at an angle. The vertical posi- 

 tion is probably the most common, as there are more vertical 



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engines. The valves 



are generally oper- 



V co//ar ate( j by a cam s haft. 



In a four-stroke cycle 

 engine the valves open and close 

 once for each two revolutions of 

 the crank shaft. The speed of 

 the cam shaft, then, must be half 

 that of the crank shaft. This 

 is accomplished through a re- 

 ducing gear. It is not possible 

 to change the valve timing a great 

 deal from that which was predetermined by the manufac- 

 turer. The cam shaft and cams are forged integral, and the 

 gear is keyed or pinned on. A changing of the meshing of 



Fig. 412 



Spring 

 retainer pin 



The parts which make 

 up the valve assembly 



