Since the newly developed M40 engine differs from the previous M10 engine primarily in the removal of the cylinder head, these works are combined in a special section in this book. All other sections («Lubrication system, cooling system, supply system etc.») also apply to the M40 engine, which has been installed since September 1987. (on the 316i from September 1988 and on the 318i from September 1987.).
The design of the new M40 engine is similar to the previous four-cylinder engine (M10). The most important innovation is the drive of the gas distribution mechanism, which is carried out here by a toothed belt. In addition, hydraulic valve clearance compensation has been introduced.
The camshaft operates the valves through rocker arms supported by hydraulic valve clearance compensators. Thanks to this, valve clearances are automatically compensated, which eliminates the need for valve adjustment. Exhaust valves are filled with sodium for increased wear resistance. The camshaft is mounted in 5 separable bearings. The camshaft is driven from the crankshaft via a toothed belt.
The operation of the lubrication system is provided by a Duocentric type oil pump located in the cover of the timing gear housing and is driven directly from the crankshaft.
The power supply system is based on a Motronic type fuel injection device, (see section «fuel injection device»).