BMW M40 and M43 Four Cylinder Engines

 

M43TU showing plastic intake manifold and coil pack.

Chronology

The BMW M10 four cylinder engine had been a marvel. Since the 1960s this engine had been the bedrock of the companies success in smaller cars and had even been the basis of a highly successful Formula 1 engine. It's M40 successor would have a tough act to follow. But the M40 wasn't really meant to be the next M10. Cars were heavier, engines getting larger and more of BMWs output would use six cylinder power plants. For those who wanted a sporty four cylinder the M42 16 valve would fit the bill. The M40 1.6 and 1.8 were for economy minded owners for whom power wasn't the most important factor. This is one reason why there was no 2.0 version.

The M40 entered service in 1987 for the E30, M10 E30s had chrome bumpers and the face lifted cars had plastic versions with an M40. Early E36s and the E34 518i also used the M40 until the arrival of the M43 in late 1993. A handful of early Z3s may have had M40s but I suspect these were all sold in Germany.

The run out M43TU was mainly sold as the 1.9, only high tax markets such as Greece saw the 1.6. With the demise of the M44 16 valve the M43TU also found a home in the Z3 and E36 Compact, but it was no match for an M44.

The M40s were never intended to be high performance engines and that's how they drove. Even in the lighter E30 the driver often wanted more power and things ran out of puff about 4500 rpm (just when the wonderful M42 came on song). It's likely for this reason that all USA E36s had the M42 instead, not just the coupe. The 1.6 was never enough. In the E46 318Ci and post-face lift Z3 the lack of a 16 valve alternative really did make a six cylinder the desirable option. As for the E34 518i, you wouldn't want to be in a hurry.

M43 in an E36 318i.

Design

The M10 and M40 differed in many ways, largely due to the fact that the M10 had been in production for around 20 years with minimal change. The most controversial feature was the timing belt, this made the engine cheaper and quieter but had to be changed regularly so was a damn nuisance. Access to change it was good luckily. On the plus side the hydraulic tappets never needed to be adjusted unlike the M10's manual arrangement.

Fuel injection was always Bosch Motronic and to this end the distributor was mounted directly to the end of the camshaft, there was no need for vacuum advance as this was electronically controlled. Other than it's cam belt the M40 was a lower maintenance engine.

The M43 went back to using a chain, hurray! BMW sighted the main reason as being higher engine bay temperatures shortening belt life. Cars with lower front were getting less cooling air and catalytic converters generated a lot of heat.

In addition to its chain the M43 got the low friction roller style of cam followers used on the M44. The DISA variable length intake system system pioneered on the later batch of E36 M42s helped to boost torque.

The M43 binned the distributor in favour of one coil per cylinder but unlike the sixes the coils lived in pack at the side of the engine and used HT leads. The knock detection system from the later M42s was fitted. There was only a modest rise in power but the torque curve was fatter and emissions were a good deal lower.

For 1998 The M43TU brought a few last minute improvements. This was a 1.9 in almost all markets but was offered with 118bhp or a detuned 105 (sold as a 316i). Balancer shafts were added to improve smoothness at the expense of higher rotating mass. It used an electronically controlled thermostat like the M54 and changed the air flow meter for a MAF. A handy recognition feature is that the M43TU has a plastic rather than cast aluminium intake manifold.

Variants

Code	Size	Power bhp@rpm	Torque lb/ft@rpm	BHP/ litre	Torque/ litre	Manufactured	Bore x Stroke	Timing	Weight (kg)	VANOS	Used in
M40	1.6 1.8	102 @ 5500 115 @ 5500	105 @ 4250 122 @ 4250	63.8 63.9	63.8 67.8	87 -> late 93	84x72 84x81	Belt	81	No	E30 316i, 318i E34 518i E36 316i, 318i.
M43	1.6 1.8	102 @ 5500 115 @ 5500	111 @ 3900 124 @ 3900	63.8 63.9	69.3 68.9	late '93 -> late 98	84x72 84x81	Chain	83	No	E36 316i, euro 318i (not Coupe), E34 518i
M43TU	1.6 1.9	103 @ ? 118 @ 5500	122 @ ? 133 @ 3900	54.2 62.1	64.2 70	98 on	85x83.5	Chain	88	No	E36 compact, Z3 E46 318i

 

M40 in an E30.

Problems

The M40 developed a reputation for sounding like a sewing machine once you'd put a few miles on it. I bought a very cheap 1988 318i touring that needed a new camshaft because the previous owner never checked the oil level. I fitted a camshaft and new tappets, it still sounded nasty. I've come to the conclusion that the noise must be due to worn valve guides, so not easy to fix. I don't know if the M43 fixed this but I'd be interested to hear from owners.

Of course any engine with a cam belt needs a new one now and then. It's not just the miles but they can crack and age over time too, certainly five years is too much. It was a collision engine so if it snapped it was new engine time. At least it was easy to change and access was good.

Bad running could be caused by a worn air flow meter on the M40 and M43 (not TU). But these were often wrongly blamed. The "Bosch specialist" told the previous owner of a 318i I bought that he needed a new one but all that was wrong was the throttle cable was too tight and wasn't allowing the throttle position switch to click at idle.

To be honest they were pretty reliable if serviced regularly.