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SUCCESSFUL FARMING 



stroke, in which the charge of air and gas is mixed in the right proportions 

 to give an explosive mixture. The second stroke compresses the charge 

 of air and gas which was previously drawn into the cylinder. The third 

 stroke is the working one in which the compressed charge of air and gas is 

 exploded and the energy hurled against the piston head. The fourth 

 stroke is the exhaust, or elimination of all the old gases which were burned. 

 Therefore, the four-cycle engine requires two revolutions of the fly wheel to 

 complete the four strokes necessary for obtaining power from this type of 



engine. The four- 

 cycle engine requires 

 two openings which 

 are provided with 

 valves held tightly in 

 place by springs. 

 These valves are oper- 

 ated by mechanical 

 means, although in 

 some engines the in- 

 take valve is operated 

 by suction. 



The two-stroke 

 cycle or two-cycle 

 engine requires two 

 strokes of the piston 

 in securing one work- 

 ing stroke. Therefore, 

 this engine theoretic- 

 ally receives twice the 

 power per square inch 

 hurled against the pis- 

 ton that the four-cycle 

 engine does. The 

 crank case of such an 

 engine must necessa- 

 rily be airtight, because the charge of air, or sometimes a mixture of air and 

 gas, is brought into this part on the up-stroke of the piston and on the down- 

 ward stroke the burned gas passes out of the exhaust port while the new gas 

 from the crank case enters the combustion chamber. It is, therefore, 

 entirely necessary that the crank shaft which runs through the crank case 

 fit airtight in its bearings. This is a condition which is difficult to maintain, 

 especially in an old engine. This type of engine does not operate with 

 valves at the intake and exhaust, but operates with ports or openings which 

 are opened and closed by the piston passing over them. 



About 90 per cent of all the gas engines used for agricultural purposes 



1 Courtesy of Ellis Engine Company, Detroit, Mich. 



Sectional View of a Two-Cycle Engine. 1 



