Definition
The hardened steel pin that connects a piston to the small end of the connecting rod, allowing the rod to pivot as the piston moves up and down in the cylinder. In American usage it is more commonly called a piston pin or wrist pin.
Plain English
The pin that joins the piston to the connecting rod. It lets the rod rock back and forth as the piston travels up and down inside the cylinder.
Context Anchor
Seen in piston-engine maintenance, especially during cylinder removal, piston inspection, engine overhaul, and parts replacement.
Derivation
From the old shipbuilding term gudgeon, a metal socket that holds a pivoting pin (used on rudder hinges). The name carried over to engines because the pin performs the same job: a pivot point that lets one part swing on another. British engineering kept the term; American practice usually calls it a piston pin or wrist pin.
Why Pilots Care
Pilots rarely deal with this part directly, but understanding the term matters when reading maintenance logs, overhaul records, or engine literature -- especially British or international sources -- so they can recognize that a gudgeon pin, piston pin, and wrist pin all refer to the same component.
Analogy
It works somewhat like the pin in a door hinge: the parts are held together, but they can still pivot around the pin.
Intuition Check
Do not think of a gudgeon pin as a small locking pin or simple fastener. In an aircraft engine, it is a load-carrying pivot pin inside the piston.
Example Sentence 1
During the top overhaul, the mechanic inspected each gudgeon pin for wear before reinstalling the pistons.
Example Sentence 2
Proper lubrication of the gudgeon pin prevents seizure and extends piston life.