Dead centre (engineering)

In a reciprocating engine, the dead centre is the position of a piston in which it is either farthest from, or nearest to, the crankshaft.

In a reciprocating engine, top dead centre of piston #1 is the point from which ignition system measurements are made and the firing order is determined.

[citation needed] Top dead centre for cylinder one is often marked on the crankshaft pulley, the flywheel or harmonic balancer or both, with adjacent timing marks showing the recommended ignition timing settings as decided during engine development.

For example: The concept of top dead centre is also extended to pistonless rotary engines, and means the point in the cycle in which the volume of a combustion chamber is smallest.

Steam locomotives normally have at least two double acting cylinders, which enables the cranks to be set so that at least one piston will always be off the dead centre and no starting assistance is required.