M40
• Hydraulic valve lash adjusters: no adjustment needed • Timing belt: quiet operation but requires replacement every 100k km • Lightweight design with aluminium head
The BMW M40 is an inline four-cylinder petrol engine produced from 1987 to 1994. It replaced the outdated M10 and was used in the E30 and E36 models. The M40 featured a lighter design with a cast iron block, aluminium head, and single overhead camshaft (SOHC). For the first time in a BMW engine, hydraulic valve lash adjusters were used, eliminating the need for valve clearance adjustments. A timing belt replaced the chain, reducing noise but requiring replacement every 80,000–100,000 km. Displacement was 1.6 or 1.8 litres, with power up to 115 hp (M40B18). Criticised for increased noise and cooling system issues, it remained economical and reasonably reliable. Many units served over 250,000 km with proper timing belt and coolant maintenance.