Inline engine

An inline engine is a piston engine that has its pistons arranged in cylinders in rows, in (a) line. This is as opposed to the radial engine, where the pistons are placed in individual cylinders, arranged like the spokes of a wheel around the central crankshaft.

Inline engines represent the vast majority of piston engines today. Almost all 4-cylinder engines use the inline design. They are considerably easier to build because the cylinder banks and engine block can be milled from a single block of metal. This simplicity is offset somewhat by the common need for liquid cooling. Inline engines are also much smaller in volume than designs like the radial, and can be mounted in any direction.