Definition
A rotating shaft in a reciprocating engine that carries a series of lobes (cams) which open and close the intake and exhaust valves at precisely timed points in each cylinder's operating cycle. In an aircraft piston engine, the camshaft is driven by the crankshaft through gears and turns at half crankshaft speed in a four-stroke engine.
Plain English
A long shaft inside the engine with bumps along it. As it spins, the bumps push the engine's valves open at exactly the right moments so air and fuel can come in and exhaust gases can go out.
Context Anchor
Seen in aircraft piston engine descriptions, maintenance records, and discussions of valve timing or internal engine wear.
Derivation
From 'cam' (an offset lobe or projection on a shaft that converts rotary motion into reciprocating motion) and 'shaft' (a rotating rod). The word 'cam' comes from the Dutch 'kam,' meaning 'comb' -- because the row of lobes along the shaft resembles the teeth of a comb.
Why Pilots Care
Valve timing controlled by the camshaft directly affects engine power, smoothness, and reliability. Camshaft wear or lobe damage shows up as rough running, power loss, or abnormal compression -- things a pilot may first notice during runup or in cruise.
Intuition Check
Do not confuse the camshaft with the crankshaft. The crankshaft handles the main turning force of the engine; the camshaft times the opening and closing of the valves.
Example Sentence 1
During the engine overhaul, the mechanic inspected each camshaft lobe for wear before reinstalling it.
Example Sentence 2
Correct camshaft timing ensures the valves open and close smoothly with each piston stroke.