Wrist Pin
A steel pin that pivotally connects the piston to the small end of the connecting rod.
A wrist pin (also known as a gudgeon pin) is a precision-ground steel pin that connects the piston to the small end of the connecting rod. It acts as the pivot point that allows the connecting rod to swing back and forth as the piston moves up and down in the cylinder.
The wrist pin must withstand the immense combustion forces pushing down on the piston crown, as well as the rapid acceleration and deceleration forces at high engine RPMs. It is typically hollow to reduce weight and lubricated by engine oil.
Wrist pins can be held in place using snap rings (floating pins) or pressed into the connecting rod (pressed pins). If a wrist pin or its bushings wear out, it will create excessive clearance, resulting in a distinct double-knock metallic noise known as wrist pin click.
Repairing worn wrist pins requires a complete engine teardown, as the pistons and connecting rods must be removed and sent to a machine shop for replacement pins and bushings.