The BMW M40 is an SOHC straight-four petrol engine which was produced from 1987–1994.

[1][2] It served as BMW's base model four-cylinder engine and was produced alongside the higher performance BMW M42 DOHC four-cylinder engine from 1989 onwards.

Compared with its M10 predecessor, the M40 uses a belt-driven camshaft,[3] and hydraulic tappets.

Like the M10, the M40 uses an iron block and an aluminium head.

[5][6] Following the introduction of the BMW M43 engine in 1991, the M40 began to be phased out.