Stroke (engine)

Reciprocating motion, used in reciprocating engines and other mechanisms, is back-and-forth motion. Each cycle of reciprocation consists of two opposite motions: there is a motion in one direction, and then a motion back in the opposite direction. Each of these is called a stroke. The term is also used to mean the length of the stroke.

In a steam locomotive, steam, Otto or Diesel piston engine, a stroke is the action of a piston travelling the full length of its locomotive cylinder or engine cylinder in one direction.

The stroke length is determined by the cranks on the crankshaft. Stroke can also refer to the distance the piston travels. Bore is the diameter of the cylinder, which means that engine displacement is dependent on both the bore and the stroke of the cylinder.

In a pistonless rotary engine, the term is applied to the corresponding rotor movement, see dead centre.