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AGRICULTURAL ENGINEERING 



revolution to two of the crank shaft, is not required, and in 

 many engines the main valves are dispensed with by making 

 the piston uncover ports or openings in the cylinder walls for 

 the admission of fresh gases and the escape of those burned. 

 This simplicity of construction enables the two-cycle engine 



Fig. 222. Illustrating- the operations which take place in the two-stroke 

 cycle engine. A, suction into crank case. B, compression in crank 

 case. C, compression in cylinder combined with A. D, expansion in 

 cylinder combined with B. (From Farm Machinery and Farm Motors.) 



to be built and sold at a lower cost than the four-stroke cycle 

 engine. 



On the other hand, the two-cycle engine does not operate 

 with the same economy in fuel consumption as the four-stroke 

 cycle. If the cylinder diameter is large, the mixing of the 

 fresh and burned gases is so great that there cannot be the 

 best scavenging or cleaning of the burned gases from the cylin- 

 der without a loss of unburned gases to the exhaust. Very 

 large engines are made on the two-cycle plan by introducing 

 an auxiliary air-compression cylinder which blows air to clean 

 out the burnt gases. 



The two-cycle engine is a little more difficult to manage, 

 as a rule, and the carburetor and the ignition system are more 

 susceptible to slight misadjustments. This is no doubt 

 largely due to the fact that there cannot be as sharp a suction 

 upon the carburetor as may be had with the four-cycle engine. 



