A
two-stroke, or
two-cycle,
engine is a type of
internal combustion engine which completes a power cycle with two strokes (up and down movements) of the
piston during only one crankshaft revolution. This is in contrast to a "
four-stroke engine", which requires four strokes of the piston to complete a power cycle. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust (or
scavenging) functions occurring at the same time.