Definition
The distance a poppet valve moves off its seat when fully open in a reciprocating engine. Valve lift is determined by the shape of the cam lobe and the geometry of the valve-operating mechanism, and it controls how much airflow can pass through the valve port during the intake or exhaust stroke.
Plain English
How far a valve opens away from its closed position. The bigger the lift, the more air or exhaust gas can flow through the opening.
Context Anchor
Seen in aircraft piston engine maintenance, especially when checking valve operation or engine wear.
Derivation
“Valve” comes from an older word meaning a leaf or flap of a door. “Lift” means to raise. Together, the term points to the valve being raised off the surface it normally seals against.
Why Pilots Care
Correct valve lift directly affects how much air and fuel the engine can move, influencing power, efficiency, and reliability.
Intuition Check
Valve lift does not mean aerodynamic lift from a wing. Here, lift means the measured distance an engine valve is raised open.
Example Sentence 1
Excessive wear on the cam lobe reduced the intake valve lift, causing a noticeable drop in cylinder power output.
Example Sentence 2
During inspection the technician measured valve lift on all cylinders to confirm it remained within limits.