Definition
A circular plate inside a radial aircraft engine that has raised lobes machined onto its face. As the cam ring rotates, the lobes push the valve lifters in the correct sequence, opening and closing the intake and exhaust valves of each cylinder at the right moment in the engine's cycle.
Plain English
A spinning ring inside a radial engine with bumps on it. As it turns, the bumps press on parts that open and close the engine's valves at the right times.
Context Anchor
Seen in aircraft engine construction, radial-engine descriptions, and maintenance discussions about valve timing.
Derivation
A 'cam' is a shaped piece that converts rotary motion into back-and-forth motion by pushing on a follower as it turns. The word comes from the Dutch 'kam' meaning 'comb' — referring to the tooth-like projections. In a radial engine, the cam is shaped like a ring rather than a shaft, so the cylinders arranged around it can each be operated by the same rotating part.
Why Pilots Care
Correct cam ring function maintains proper valve timing essential for engine power and reliability.
Intuition Check
A cam ring is not just a plain ring, seal, or spacer. Its shaped raised areas are what make it control valve movement.
Example Sentence 1
During the engine overhaul, the mechanic inspected the cam ring lobes for wear before reinstalling it.
Example Sentence 2
Radial engine overhaul manuals specify clearances between the cam ring and followers.