126 SCIENCE OF THRESHING. 



counterbore. The counterbore of the cylinder ends 

 is to prevent the formation of shoulders from the 

 wear of the piston, and its subsequent pounding, 

 which would take place if the cylinder were originally 

 of one diameter throughout its length. 



In packing the stuffing boxes, it is desirable that 

 the packing be placed as evenly as possible around 

 the rods, and the glands be drawn home as evenly as 

 possible, so as to prevent undue pressure on either 

 side of the rods. Inasmuch as the rod may not run 

 exactly true, and is rarely of exactly the same diam- 

 eter throughout its length, the packing must be 

 elastic. Long usage sometimes glazes and hardens 

 the packing; when in this condition, the gland should 

 not be forced up as the rod will become cut and there 

 will be excessive friction and consequent loss of 

 power. 



One side of the crank disc is made heavier than the 

 other to counterbalance the weight of the connecting 

 rod and reciprocating parts. This is done to prevent 

 the vibration which would otherwise take place, 

 racking the engine and alternately tightening and 

 slacking the drive belt. 



The journals on this part of the engine should 

 receive great care and not be allowed to become 

 loose from wear and thereby occasion knocking and 

 pounding. The pillow block or bearing in which the 

 main shaft of the engine runs should be kept suffi- 

 ciently tight so that the shaft will run true and also 

 to withstand the pressure of the piston and connecting 

 rod. The bearing may be tightened by removing a 



