Definition 1 of 2
Definition
In a reciprocating engine, the precise scheduling of two key events relative to the position of the piston: the opening and closing of the intake and exhaust valves (valve timing), and the firing of the spark plugs (ignition timing). Timing is expressed in degrees of crankshaft rotation before or after top dead center (BTDC or ATDC) or bottom dead center.
Plain English
Timing is making sure the engine's valves open and close, and the spark plugs fire, at exactly the right moment as the piston moves up and down. If these events happen too early or too late, the engine won't run properly.
Context Anchor
Seen in aircraft engine maintenance, ignition system checks, engine troubleshooting, and discussions of rough running or poor power.
Derivation
Timing comes from the word time, meaning to choose or measure the moment when something happens. In this aviation use, it is not about clock time; it is about the exact moment an engine event happens during the engine's repeating cycle.
Why Pilots Care
Correct timing produces efficient power and prevents engine damage from detonation or overheating.
Intuition Check
Do not read timing here as scheduling or clock time. In this context, timing means the exact point in an engine cycle when an action is set to happen.
Example Sentence 1
The mechanic adjusted the magneto timing so the spark would fire 25 degrees before top dead center.
Example Sentence 2
Advanced timing improved climb performance but required careful monitoring to avoid detonation.