Definition
A pivoting lever in a reciprocating engine's valve train that transfers motion from the pushrod (or camshaft, in overhead-cam designs) to the intake or exhaust valve, pushing the valve open at the correct moment in the engine cycle.
Plain English
A small lever inside the engine's cylinder head that gets pushed up on one end so the other end pushes a valve open. When the push stops, a spring closes the valve again.
Context Anchor
Seen in piston-engine maintenance discussions, especially when inspecting valve covers, valve clearance, push rods, and valve operation.
Derivation
Called a rocker arm because it physically rocks back and forth on a central pivot — one end goes up, the other goes down, like a seesaw.
Why Pilots Care
Proper rocker arm function maintains correct valve timing and lift; worn or bent arms can reduce engine power or cause valve damage.
Analogy
Think of a seesaw. Push one end down and the other end goes up. The pushrod shoves one end of the rocker arm up, and the other end pushes the valve down to open it.
Intuition Check
Do not read “rocker arm” as just any arm-shaped bracket or support. In an engine, it is a moving lever that rocks on a pivot to open a valve.
Example Sentence 1
During the top overhaul, the mechanic inspected each rocker arm for wear at the pivot point and valve contact face.
Example Sentence 2
A cracked rocker arm was found to be the cause of the low compression reading on cylinder three.