5i2 



ENGINEERING ON THE FARM 



crank must be counterbalanced in order to reduce vibration. 

 (See Fig. 407.) 



A three-cylinder engine is not commonly built. It is 

 used to a limited extent in both the two- and four-stroke 

 cycles for marine engines. The cranks are set 120 apart. 



Counter weights. 



.Main bearings. 



CE 



S 



HD 



^Crank bearingh 



Fig. 407. Two types of two-cylinder crank shafts. At the left the cranks 

 are i8o° apart, at the right j6o° apart. 



In a four-cylinder engine (Fig. 408) an impulse is delivered 

 each quarter of 720 , or each half-revolution. A four- 



Ma/'n bearinas 



Fig. 408. A typical three-bearing four-cylinder or four-throw 



crank shaft 



cylinder crank shaft is made with 180 between the first 

 and second throw. The second and third lie side by side 



A7a/n hearings- 

 Fig. 409. A three-bearing six-cylinder or six-throw crank shaft 



and pointing in the same direction, but are considered as 

 being 360 apart, since that is the smallest turning move- 

 ment possible between impulses delivered to these two 



