A four cylinder motorcycle is distinguished from other engines by having four driving pistons and connecting rods to the engine's crank shaft. Typically the cylinder configuration in an inline formation.
The cylinders operate with one piston at the top of a stroke, another in mid-stroke, while the third is at the bottom of a stroke whether in a two stroke or four stroke engine thus creating a engine balance. Four cylinder motorcycles can have twin or a quad exhaust system.
The straight-4 engine is much smoother than one, two, and three cylinder engines, and this has resulted in it becoming the engine of choice for most economy cars, although it can be found in some sports cars as well. However, the straight-4 is not a fully balanced configuration.
Motorcycles using a four cylinder configuration: