THE INTERNAL -COMBUSTION TRACTOR 87 



to form a shoulder at the end of the piston stroke. In the latter 

 case both this ring and the one at the other end of the piston 

 are allowed to travel half their width beyond a counterbore, 

 or enlargement of the cylinder diameter. In the absence of 

 some such provision the end of the piston wears the cylinder 

 until a shoulder is formed, and if at any time the length of the 

 connecting rod is even slightly increased, knocking in the cyl- 

 inder will result. Where splash lubrication is used, this ring 

 wipes the excess oil back into the crankcase. The cylinder 

 rings are of cast iron and machined to size. After being 

 ground to a size larger than the cylinder, a segment is cut out. 

 The ring is then compressed into place so that its tension causes 

 it to fit snugly against the cylinder wall. 



CONNECTING ROD 



About midway of the piston there are interior enlargements 

 or bosses for supporting the wristpin, to which the connecting 

 rod is attached. The wristpin itself is usually hollow and 

 provided with holes for lubricating its bearing with the oil col- 

 lected from the cylinder wall. The connecting rod, which 

 transmits the power from the piston to the crankshaft, is usually 

 of I-section, drop-forged steel, as on the best locomotive and 

 marine steam engines. There are numerous devices for at- 

 taching the connecting rod to the crankpin, it being frequently 

 necessary to withdraw the piston and connecting rod to examine 

 the former. The same devices serve to provide adjustment 

 for wear. The most common and probably the most satis- 

 factory method is a removable cap attached to the connect- 

 ing rod by bolts on either side of the crankpin. Both ends of 

 the connecting rod are commonly lined with an anti-friction 

 material, most of which goes under the name of Babbitt-metal. 



CRANKSHAFT 



The crankshaft must be proportioned to meet the strain 

 which is placed upon it, and must be well supported by wide 



