Verify the individual car
This page describes a model, engine or historical subject at archive level. Before using a specification for purchase, valuation or repair, confirm the chassis identity, production date, market version and installed parts of the individual car. Previous repairs and conversions can change what is present. Use the linked factory material for exact procedures and record measurements and observations rather than relying on appearance alone.
A more modern everyday engine
Hydraulic tappets, Motronic management and a belt-driven camshaft make the M40 feel like a step into the late 1980s. It is not a performance icon, but in a light 316i or 318i it offers useful economy, straightforward parts availability and enough pace for relaxed road use.
Camshaft wear
A pronounced top-end clatter, reluctance to rev and visible scoring under the oil cap can point to camshaft and follower wear. Oil quality and neglected spray-bar lubrication are relevant. Diagnose before buying parts: noisy injectors, a loose exhaust shield or tired accessories can imitate internal noise.
Belt history is non-negotiable
As with the M20, documentary proof matters. Replace an unknown belt and tensioner immediately and inspect oil seals that could contaminate the new belt. A clean cooling system and correct thermostat help the small four-cylinder work at its intended temperature.