Definition
A hardened steel pin that connects the piston to the small end of the connecting rod, allowing the piston to pivot on the rod as it moves up and down inside the cylinder. The pin passes through bosses in the piston and through a bearing in the connecting rod, and is normally retained by circlips or plugs at each end to prevent it from sliding out and contacting the cylinder wall.
Plain English
It is the short metal pin that joins the piston to the top of the connecting rod, letting the piston tilt slightly while still being firmly attached to the rod that drives the crankshaft.
Context Anchor
Seen in piston-engine maintenance, especially during cylinder removal, piston inspection, and engine overhaul.
Derivation
Sometimes called a wrist pin because the joint it forms acts like a wrist — a small pivot point allowing the piston to rock slightly relative to the connecting rod as the rod swings during crankshaft rotation.
Why Pilots Care
A worn or broken piston pin can cause engine seizure or loss of power.
Analogy
A piston pin works a little like the pin in a door hinge: it holds two parts together while still letting them move around the pin.
Intuition Check
Do not picture a small light pin like a safety pin. A piston pin is a strong, precision-fit engine part that carries heavy loads inside the cylinder.
Example Sentence 1
During the engine overhaul, the technician inspected each piston pin for wear before reassembling the pistons onto the connecting rods.
Example Sentence 2
Proper lubrication keeps the piston pin from overheating during operation.