Straight-twin

A straight-twin engine is a two cylinder piston engine that has its cylinders arranged in a single row.

Straight-twin designs are mostly used on motorcycles.

Most of the British four-stroke cycle straight-twin engines had a crank angle of 360°, which means that both pistons have to be in the same position and move in same direction all the time. This lead to a working cycle every 360°. The vibrations are worse than with a similar displacement one-cylinder engine because the forces of both cylinders add up.

Japanese motorcycles, with the exception of Yamaha, use a crank angle of 180°. This leads to less vibrations but uneven firing. The engine sound of of these engines is distinctively different.

With two-stroke cycle, the crank angle is generally 180°, and a working cycle every 180°. Such an engine will produce less vibrations.

See also: straight engine