CRANKSHAFT four engine 3D model

A straight-four engine (also called an inline-four) is a four-cylinder piston engine where cylinders are arranged in a line along a common crankshaft.The majority of automotive four-cylinder engines use a straight-four layout  (with the exceptions of the flat-four engines ) and the layout is also very common in motorcycles and other machinery. Therefore the term four-cylinder engine is usually synonymous with straight-four engines. When a straight-four engine is installed at an inclined angle (instead of with the cylinders oriented vertically), it is sometimes alled a slant-four.