Two-cylinder engines are known as twins. The parallel twin as in most common British and many Japanese motorcycles. Engines of this design typically have the cylinders side by side vertically above the crankcase, with the exhaust ports pointing forward to maximize airflow cooling. Longitudinal twins include the 500 cc Sunbeam S7 and S8. The two crankpins can be timed simultaneously, with each side firing alternately every 360° (most British bikes), or timed with 1 piston at TDC and the other at BDC to fire 180° apart, followed by a long "dead" interval (many Hondas). Some Hondas have been made with both crankshaft types. Some engines, such as the Matchless 650, have had a 3rd center main bearing between the crankpins, but this was not successful.

The parallel-twin engine configuration was made famous by Edward Turner's Triumph Speed Twin design as used on the Bonneville 20 years later.