The highest point of travel for a piston inside the cylinder, marking the transition between the compression and power strokes. Mechanics use this position as the absolute reference point for setting ignition timing, valve lash, and camshaft synchronization. A timing mark on the harmonic balancer or flywheel usually aligns with a pointer on the engine block to indicate this position for the number one cylinder.
Bring cylinder one to top dead center on the compression stroke before you drop the distributor in.
Always verify whether the engine is at TDC on the compression stroke or the exhaust stroke, as the timing marks align twice per full four-stroke cycle.
Also heard as
- TDC
Do not mix it up with
- Bottom dead center: Bottom dead center is the lowest point of piston travel, exactly 180 crankshaft degrees away from top dead center.
Related terms
Bottom dead center
The lowest point of a piston's travel within its cylinder during an engine cycle.
Ignition timing
The exact moment a spark plug fires relative to the position of the piston during the compression stroke.
Harmonic balancer
A weighted pulley mounted to the front of the crankshaft to absorb torsional vibrations.
Cylinder head
This cast metal component bolts to the top of the engine block to seal the combustion chambers.