BMW M42 and M44 Four Cylinder Engines

BMW M42 engine

M42 in my own E30 318iS, lovely.


The M42 was introduced in 1989 to power the glorious E30 318iS, a simply fantastic car in the spirit of the 2002tii. It revved like a banshee and came on cam just when the 318i's 8 valve M40 was running out of puff. This was the engine the E30 had always needed to beat the Golf GTI. It introduced many new technologies for BMW and got rid of the M40's timing belt and distributor.

When the E36 took over from the E30 only the 318iS Coupe got the M42, the others made do with the M40 (except in the USA and South Africa). The E36 was a heavier car and with the M42 it showed, it was still good but not as much fun as the E30 318iS.

In 1996/7 the M44 grew to a 1.9 and had a few technological improvements, but peak power remained the same. This engine saw service in the Z3 where it worked very nicely.

Alpina and Schnitzer made 2.1 M44s with a plate between the head and block to allow a longer stroke, these made 170bhp. There was also a popular super charger option from Dowling Atlanta (DASC) which made over 200.

The truth is that the M42 was a victim of it's own success. At launch it made more power than the M20 2.0 and the marketing department doubtless wondered what was going on. Of course the M42 was a revvy sporty engine, the M20B20 was more of a torquey engine and had it's own place. But this doubtless reigned in development and the frustration of the engineers was palpable. I've seen M42s with minor mods making over 160bhp.

The M42 is my favourite BMW engine. It's bullet proof and great fun. The S42 racing version made over 300bhp.

BMW M44 engine

M44 1.9, note the different intake manifold and MAF.


The M40 used similar technology to the M20 little six but the M42 was bang up to date and was basically two thirds of an M50. Compared to the M40 the new engine has four valve per cylinder with maintenance free hydraulic tappets. It had one coil per cylinder instead of a distributor, although unlike the M50 the coils were in a remote pack with HT leads rather than directly on top of the spark plug, no idea why. Thankfully it went back to using a timing chain instead of a belt. These engines always had a nice tubular exhaust manifold which contributed to their sporty nature.

However the M42 shared the air flow meter technology with the M40 until the arrival of the M44 when a MAF replaced it.

M42s had a strong forged crankshaft and a drop-in oil filter housing as found on the M50. Stroker 2.1 engines used the crank shaft from the M47 diesel engine.

When fitted to an E36 the M42 used DISA technology to give a variable length intake path and thus increase mid-range torque. E36 M42s also gained electronic knock detection as used on the M50. There were various minor changes throughout the M42's life, for example even on the E30 there were two styles of throttle body heater (most BMW engines have this to prevent icing in very cold weather).

In addition to another 100cc the M44 brought in new low friction valve gear using bearings on the rocker arms where they touched the cam lobes. Alas it used a cheaper cast crankshaft.

It switched from Motronic 1.7 to 5.2. This had to be programmed via an RS422 interface rather than just swapping out a socketed chip. The M42 used OBD-I electronics, the M44 was OBD-II.

Some markets used a single mass flywheel and others used dual mass on either engine. Both were a bit heavy and one thing I'd love on my car is a lightweight flywheel, cheap swap is an M20 but you need the starter motor too.

The M44 used a serpentine belt instead of individual fan belts. If you're so inclined M44 bits for this will fit the M42.

I must mention Metric Mechanic here. If you ever want to improve your M42's performance they have the parts and the knowledge to build a normally aspirated 210 bhp engine. You should download their M42 catalogue and drool.


Code Size Power
Manufactured Bore x
Timing Weight
VANOS Used in
M42 1.8 140 @ 6000 129 @ 4500 77.8 71.7 89 - 96 84x81 Chain 100 No E30/E36 318is, 318ti
M44 1.9 140 @ 6000 133 @ 4300 73.7 70 96 - 99 85x83.5 Chain 102 No E36 318iS, 318ti, Z3


BMW M42 engine

Heavens! There's TWO of them!


These were good engines and one of mine had over 215,000 miles on it last I heard. They tend to use the revs more than the six cylinder engines so good quality oil is important and I use Mobil 1 0w40, I'd not bother with that on a six.

The timing case profile gasket was initially made from the wrong material and failed, mine went on a '93 E36 318iS under warranty luckily. Big job as you need to remove the head to fix it. If a car was going to fail it'd have done it by now, any engine you're looking at will have a new gasket.

If it's rattly try a new timing chain tensioner, very quick and cheap fix. The newer ones are an improved design. I bought a car that had been run with a worn one too long and eventually had to fit a new chain, sprockets and guides which cost about 300 quid in parts.

The O rings that seal the valve cover above the spark plug recesses can leak and let oil pool around the spark plugs. Easy to spot, just pull the HT lead and look for oil.

Ham fisted mechanics can easily over tighten the bolts that hold down the valve cover. This leads to oil leaks. You could use a heli-coil to re-thread the hole but on mine I bought a new upper timing case cover.

I once had an annoying rattle due to the tray carrying the HT leads fracturing one it's mounts and banging against the head.

Some of the intake tubing around the idle control valve can be poor quality and disintegrate leading to vacuum leaks and poor running. I think it must have been some bad batches as I've only seen it on one engine.

There are two one inch long rubber hoses connecting the fuel rail to the outside world. If you get a fuel smell check them out, you need to remove the top half of the intake manifold but that's not a hard job.

If it miss-fires and need a new crankshaft position sensor pay up and get a genuine BMW one, after market ones can be problematic.

Some owners have reported problems with the two part oil pan used on the E30 M42. Bolts can back out and get sucked into the oil pump. If you have a chance it's worth dropping the sump and redoing the bolts with new thread lock. The sump is very low at the front, a problem if you have a lowered car and a street with big speed bumps. But it also makes oil changes a breeze.

On the E30/E36 the air box is a wee bit restrictive at high revs. I got a toilet waste pipe from B&Q for 85p and fitted it between the headlight cover and a larger hole in the air box, it even came with a rubber gasket which sealed everything beautifully. Amazing difference in the high end.

The Z3's air box is a joke. It takes it in on one side, then through a long pipe over the top of the radiator and into an air box that's full of padding and junk. It's quiet but very restrictive. There are nicer fixes, but the cheap one is to drill a hole in the bottom of the air box and ditch the padding from the inside. It shouldn't be affected by warm air from the engine bay if you do it right.

Anyone who fits an automatic gearbox to this engine has no soul. It's all about top end revs and the auto box kills it stone dead. Don't even think of getting this as a slush box, get a six cylinder if you must.