Definition
The raised, eccentric portion of a camshaft that pushes against a follower or valve lifter to open an engine valve at the correct moment in the combustion cycle. As the camshaft rotates, the lobe lifts the follower; as the lobe rotates past, a spring returns the valve to its closed position.
Plain English
The bump on a rotating shaft inside the engine that pushes a valve open at the right time. When the bump rotates past, a spring closes the valve again.
Context Anchor
Seen in aircraft piston engine discussions, especially when learning about valve operation, engine timing, inspections, and engine wear.
Derivation
Cam comes from an old word for a projection or notch on a wheel that produces motion in another part. Lobe comes from the Greek lobos, meaning a rounded projection. Together they describe exactly what the part is: a rounded bump on a rotating wheel that produces motion.
Why Pilots Care
Correct cam lobe shape and condition are essential for proper valve timing, engine power, and reliability.
Intuition Check
A cam lobe is not a separate loose bump added to the engine. It is a shaped raised area on the cam or camshaft that is designed to push another part at exactly the right point in rotation.
Example Sentence 1
Oil analysis revealed iron particles, suggesting wear on one of the cam lobes.
Example Sentence 2
A flattened cam lobe will prevent a valve from opening fully and reduce engine power.