LO 7-6 Identify and explain the purpose, function, and construction of piston pins

Piston Pins

Piston pins, also called wrist pins or gudgeon pins in service literature from the United Kingdom and Japan, are the connecting joint between the connecting rod and the piston. Piston pins may be either hollow or solid and are fabricated from high-alloy steels. The area of the piston pin bore of a piston is referred to as the pin boss . This area is reinforced, since the thrust forces of combustion are transmitted through the piston to the pin through the pin boss.

Semi-Floating Piston Pins

There are a variety of piston pin designs. One design is the semi-floating wrist pin. This design requires the piston pin to be pressed into the connecting rod and piston pin bore. In this arrangement, only the piston rotates on the pin while the pin is fixed by an interference fit with the rod. Assembling and disassembling the pin requires several tons of force using a special fixture to prevent damage to the piston. The advantage of this pin design is that it does not have the problem of pin-retaining clips loosening and falling out. This configuration is not commonly used on diesel engines, since wear is concentrated only on the piston pin bore and not evenly distributed across the connecting rod bushing.