M40 Engine

The M40 engine is the modern equivalent of the M10, but without the charisma. A four cylinder, single overhead cam, iron blocked workhorse, with a good strong bottom end, with a top end prone to head cracks, rapid cam wear. Power output an unspectacular 105hp for the 1600cc unit and 115hp for the extra 200cc of the 1800.

Not much in the way of tuning parts around for this engine, the only good bit about it is you can change the cam without taking off the head, but don't bother, chuck it in the skip, and get yourself and M42 instead.

M42  Engine

A twin cam cutie, with hydraulic lifters for quiet running, and strong forged bits, depending on the year of manufacture. (Beware non forged cranks in E36 derived engines) 1800cc up to 94/95 (E30) 1900cc from 95 on. 136bhp "out the box" with plenty more to come with a little "fettling" of the 1800cc unit.

The 1800cc is the one to have being the original, high revving, highly tuneable, very economical, hooligan pleasing specification.

However, as good as it is, you must keep it cool. Make certain that you don't have a plastic impeller in the water pump, if you have CHANGE IT, they fail disastrously, and will take the rest of your little engine with it. Thermostats are another weak point and radiators should regularly back flushed. Replace the radiator if it shows any sign of weakness.

The heads of these engines are a "delicate flower" and are prone to cracking when even slightly overheated.

The cam chains and sprockets can wear out at a furious pace, and should be replaced well before the 140,000 deadline along with the chain tensioner, don't skimp the job CHANGE THE LOT! NEW CHAIN ONTO OLD SPROCKETS WILL NOT GO!