Piston: Description and Operation

PISTON AND CONNECTING ROD ASSEMBLY
The pistons are elliptically turned so that the diameter at the pin boss is less than its diameter across the thrust face. This allows for expansion under normal operating conditions. Under operating temperatures, expansion forces the pin bosses away from each other, causing the piston to assume a more nearly round shape.
All pistons are machined to the same weight, regardless of size, to maintain piston balance.
The piston pin rotates in the piston only and is retained by the press interference fit of the piston pin in the connecting rod.