The Unix Nerd's Domain

BMW Buyers Checklist - Engines



Only the best kept engines look like this!

M20 after a valve went through the piston!

Some engines are better than others. In the US there is less choice but over here things are more complex. In general BMW engines are very reliable indeed, but there are a few design faults in some models. The one thing that really determines and reliability of a BMW engine is regular servicing. An engine which has had regular oil changes and hasn't been abused can easily attain 300,000 miles before a rebuild.

See the E and M number page for engine power figures.

Timing Belts

Some engines have timing belts instead of chains. These give quiet operation but must be changed at least every 40,000 miles. Some sources advise a new belt every 30,000 miles. It isn't a huge job to change a belt but the cost of one breaking can be an engine rebuild! Make sure that you have evidence of the timing belt being replaced recently before you buy the car. Recent models with timing belts include:

Ignition

Check the HT leads connecting the spark plugs to the distributor and coil are not cracked or touching the hot exhaust manifold. A new set can be expensive from BMW but generic leads are as good and cost only a few pounds each.

You can't really check the spark plugs without removing them, replace them with a new correct set once you buy the car. I once saw a freshly serviced 1982 520i with three types of spark plug fitted, they were all the wrong type! On BMWs with a distributor (generally pre 1991) it's worth checking the rotor arm and distributor cap as worn sets can make a huge difference to power and mpg.

Fuel Injection and Problem Solving

See my Motronic Problem Solving page.

M10 from an E28 518i, Jetronic L injection.

M42 from my own E30 318iS.

Four Cylinder Petrol Engines

The are several four cylinder engine families.

The M10 ran from 1962 until 1988. Power varied from 75bhp in the 1502 to over 1250 in the Formula One car that BMW won with in 1985!! Yes, an F1 car with a production car engine block! The M10 was a superb engine, mainly found in 1.8 and 2.0 guises. Most used a single carburettor, but twin carb (2002ti) and injection engines of various types were used. There was even a 170bhp 2002 turbo in 1974.

The M10 was bullet proof. It used a timing chain instead of a belt. It's valve had to be manually adjusted every 30k miles but it wasn't a major job. the fact that it was in production for 26 years says it all.

The M10 was replaced by the M40 1.8 and 1.6 in mid-87. These were belt driven 8 valve units with hydraulically adjusted tappets and Motronic 1.x fuel injection. They were reliable units but weren't as good as the M10. For a start they needed new timing belts every 40k miles. But the biggest problem was the ticking. Once M40s had done a few miles they ticked like a sewing machine when you revved them. I tried to cure this on an '89 318i touring once and came to the conclusion that worn valve guides are the problem.

The M43 1.8 8 valve replaced the M40 in mid-93. Thankfully the old timing belt was replaced by a chain and all was well again! The M43 banished the problems of the M40 and was a decent engine. It's biggest problem was the fact that it wasn't a 2.0. The cars it was trying to pull around had become a bit too heavy for it. No US or SA E36's had M40s or M43s, they got the 16 valve M42/44 instead.

Whilst all this was going on BMW introduced a 16 valve engine in 1989. The newer M42/44 1.8 and 1.9 16 valve units are a lovely sweet revving engine with a sporty character. They are slightly underpowered for use in the E36 three series however as these cars are too heavy. The older E30 318iS is my all time favourite BMW. The M42/44 use a chain and hydraulic lifters. They were BMW's first distributor-less engine and use one coil per cylinder, this further reduces maintainance. I just can't say enough good things about these engines.

The M44 used a lower friction roller bearing system on the valve lifters. It also replaced the M42's air flow meter with a less restrictive air mass meter / hot film meter. Later M42s and all M44s had DISA adjustable length intake paths to improve torque. All M42/44 fitted to E36s had knock sensors, but not E30 bound engines. Supercharger kits work wonderfully on these and give just over 200bhp, I'd love one.

The M42 engines have only one real problem. There is cooling system gasket known as the "timing case profile gasket" which will fail between 40-80,000 miles, mine went at 57,500. This failure can cause serious head overheating and damage if not spotted, I was lucky and caught the fault. It is a six hour task to replace the gasket IF no other damage was done. Everywhere except the USA it can be repaired under BMW warranty. Cars made after 9/93 have a better gasket which lasts a lot longer and should be OK forever.

The M43 generation was replaced by BMWs ground breaking Valvetronic N42 in 2001. This engine did away with throttle bodies as we know them. Instead it used an electric motor to drive an eccentric shaft which controlled valve lift. This reduced intake restriction and enhanced throttle response. Power and economy were considerably improved. The N42 was followed by slightly enhance N43 and N46 variants.

The odd one out of these later engines was the N45. It was used in some 1.6 applications (likely to save money) and more notably in the 320Si E46 homologation special. The N45 replaced Valvetronic with a normal throttle body, this worked better at very high engine speeds and in the 2.0 version it produced 173bhp at 7000rpm.

Valvetronic is of not benefit to supercharged or turbo changed (such as turbo-diesel) engines. The lower intake restriction isn't an issue with forced induction.

Cutaway of the M52 24 valve engine.

US M3 engine from my mate Ed's car.

Six Cylinder Engines

The oldest post-war six cylinder family is the 12 valve "bix six" M30 2.5, 2.8, 3.0, 3.3 and 3.5 litre chain driven engines. They ran from the 1960s until 1993. These had manually adjustable valves just like those in the four cylinder M10. In fact the M30 and M10 share many common features. The M30 was used in the six and seven series as well as the E28 525i, 528i, 535i and E34 530i, 535i. They are capable of starship mileages and surprisingly good fuel economy. Biggest fault is worn camshafts due to loose oil bar bolts or owners letting the oil level drop too far too often.

Early US versions tend to suffer poor idle due to anti-pollution equipment but with good adjustment they run well and have heaps of power. The US variants also tended to run lower compression ratios to account for lower octance US fuel and could make up to 35bhp less than a full euro engine.

The M30 has huge mid-range torque and power. Overtaking other cars in any 3.5 litre M30 BMW is an experience never to be forgotten, all the power in the world suddenly seems to appear under your right foot. There was even a 3.2 / 3.3 turbo version for the E23 745i. Turbo M30s can be tuned to over 550bhp!

The rarest M30 powered BMW is the South African E30 333i. This used Alpina B6 3.5 engine parts to make a phenomenal machine. I've seen a twin turbo example, now that's scary ;-)

In parallel with the M30 the "little six" M20 (initially called M60) 2.0, 2.3, 2.5 and 2.7s were launched from 1979. They ran until the early 90s. These were used in the older E30 three series, E28 520i and 525e / 528e and early E34 five series. These are 12 valve belt driven engines with a good reputation. They have manually adjustable valves.

The 2.7 was used in the E30 325es (US only) and E28 525e/528e (same engine size, different names!). The "e" stood for eta, the Greek letter used to represent efficiency by engineers. These were very economical engines thanks to low revving and high gearing. They used few camshaft bearings, weaker valve springs and longer intake runners. They are sometimes used as the basis for 2.7 litre performance variants of the M20 making over 200bhp.

The first 24 valve six cylinder units were the M50 2.0, 2.5s. These are very advanced units indeed with light weight plastic intake manifolds, variable valve timing (in later VANOS models after mid-93) and double overhead cam shafts. Like the M42 four cylinder engine they had one coil per cylinder and no distributor. They made over 20bhp more than the older 12 valve engines.

In 1995 BMW replace the M50s with the M52 in 2.0, 2.5 and 2.8 variants. This engine had an aluminium block, something which caused a lot of problem for users in areas with high sulphur fuel. The M52TU solved this in March 98. The TU also replaced the single VANOS with double VANOS, power was the same but mid-range torque was improved.

The M52 was dumbed down by a restrictive intake manifold in order to meet lower German insurance groups. The 328i only makes 1 bhp more than the older 325i. But fitting the M50 intake manifold to the M52 along with a big bore throttle body and rechip can yield 240+ bhp!

When BMW replaced the M52 with the M54 around 2000 the gloves were off! The restrictive manifold went and the 3.0 produced 231bhp. 2.5 and 2.2 versions were also available.

In 2004 BMW used it's ground breaking Valvetronic technology on a six for the first time. The N52 engine which resulted is a true wonder. It produces 272 bhp from a 3.0 and it very responsive. It's super lightweight block is made from a magnesium alloy core coated in aluminium alloy.

The follow on 2007 N53 uses direct injection into the cylinders, power is the same but economy and emissions are greatly improved.

Also in 2007 BMW announced the N54 3.0 twin turbo, as used in the E60 535i and E90 335i. It uses the older M54 block for extra strength and makes 306bhp, in practice cars have been dyno tested with over 360 - unmodified!

M62 V8 and gearbox.

The sculpted look of an M60 V8.

V8 Petrol Engines

The modern V8 started life in 1993 as M60 3.0 and 4.0 litre chain driven 32 valve units with hydraulic tappets and one coil per cylinder. They were all alloy construction and this was their downfall. In certain parts of the world petrol has a high sulphur content. This eroded the cylinder walls and caused bad idling and a lack of power, BMW have replaced up to 40% in some areas! A fix was issued in the form of a chip upgrade to run the engine at a higher temperature but this adversely affected power. The M60 is a good engine, but it's not built to the same standards as older units such as the M30. Any other manufacturer would have been proud of it, but BMW could have done better.

Subsequent M62 3.5 and 4.4 units have improved cylinder liners to avoid the problem. The M62 also had a computer controlled thermostat, a first for BMW. The 4.6 M62 used in the X5 was actually an Alpina engine sold by BMW.

The N62 was BMWs Valvetronic V8 and was launched in 2003. There were 3.6, 4.0, 4.4 and 4.8 version producing up to 367bhp.

In 2008 the N63 was announced for the new X6. This was a new reverse flow V8! Twin turbos are in the V8 valley, intakes are at the sides to improve packaging. A very novel concept producing over 400bhp and 450lb/ft of torque.

V12 Petrol Engines

In 1989 BMW produced a 5.0 litre V12 M70 for the 850i and 750i/L. This was mainly done to compete with Mercedes.

The M70 had an alloy block, two valves per cylinder, chain drive, hydraulic tappets and one coil per cylinder. The //M division made an S70 5.6 litre unit for the rare 850CSi, the only two valve per cylinder //M engine. The four valve unit for the M8 was never produced. But Paul Rosche did produce an S70 based V12 for use in the McLaren F1.

The M70 was replaced by a 5.4 litre M73. This in turn was replaced by the N73 6.0 Valvetronic V12 in 2003 for the E65 750Li.

M51 diesel from a 525tds.

Old M21 from an E30 324td.

Diesel Engines

BMW make the smoothest diesel engines in the world, no question!

The M21 was a diesel version of the M20 six, it was used on the E28 and E30s in turbo and non-turbo versions. It was also used in very early E34 524td/tds. The M21 was never sold in the UK. It was available in a diesel Lincoln in the USA and a motorhome!

The M51 2.5tds is an excellent engine with great torque. It sold well in the E34 525td/tds and the E36 325td/tds. There 2.5td version lacked an intercooler and has less power as a result. Like its M50 parent it had chain drive.

The M41 four cylinder 90bhp 1.7tds used in the E36 three series is underpowered for such a heavy car but is a good engine despite that. It's basically a cut down M51.

BMW diesels stepped up gear with the introduction of the M47 2.0 four and M57 six cylinder engines in the late 90s. Both are advanced designs with variable incidence turbos, they produce very high amounts of torque for their size. The M57 designation is slightly confusing as it covers quite a few variants over many years. There are 2.5 and 3.0 M57s. One of the 3.0 versions (the 306D4) has twin turbos and produces 272 bhp with a colossal 413 lb/ft of torque!

BMW also make a V8 diesel, the M67 in 3.9 and 4.4 versions. It hasn't been made available in the UK at the time of writing.

E30 M3 S14 engine in all it's glory.

S38 3.5 in an E28 M5.

M-Tech Engines

M-Tech engines are well engineered and normally hand built. They can take the pressures of sustained high speed or track use but must be properly maintained by an expert.As a result they are more expensive to own than normal BMW engines.

This especially applies to 80's and early 90's engines such as the S14 and S38 used in the E30 M3 and M5/M6. The S14 / S38 must have periodic valve adjustments. This must be done with shims and is not a trivial procedure.

The S38 has it's root is the E39 3.0CSL racing cars of the 70s, possibly BMW finest hour in competition. These 3.0 and 3.5 24 valve monsters made up to 480 bhp, 750 with a turbo. They completely dominated 70's touring car competitions. When the E26 M1 was released in 1979 it had a 3.5 engine producing 272 bhp, a lot for the time. This evolved into the 286bhp S38 for the E28 M5 and E24 M635CSi. When the E34 M5 was released in 1991 it had a 3.6 with 315 bhp, soon to be replaced by a 3.8 with 341bhp. The 3.8 used one coil per cylinder technology.

The S14 came about with the need for an E30 based touring car. It was made in two weeks by cutting two cylinders from an S38! The S14 was a real screamer of an engine and served the company well in competition. It was initially a 2.3 but the final version grew to 2.5 litres.

When the E36 three series was given to the //Motorsport department they produced two initial Engines. An S42 four cylinder for racing and an S50 3.0 six for road use. The S50 is a very durable engine and produces 286 bhp. It has one throttle body per cylinder in the normal //M tradition. Be aware that the US spec E36 M3 has a very different engine from a euro spec car and is nearer to a normal BMW engine in many ways. The US car has one throttle body and is nearer to the M50 in design. That's not to say it's a bad engine, on the contrary it's excellent. But it was cut down to same money (so were the brakes), this made the US E36 M3 a huge seller. Subsequent US //M cars have not been treated in this way, they have similar specifications to euro cars.

The E36 M3 Evo had a 3.2 litre S52 producing 321bhp. It's VANOS gear was made by Rolls Royce Aerospace (a BMW company) and they didn't do a good job. It fails frequently and costs 1500 GBP to replace. Apparently a filter becomes clogged and causes oil starvation. This filter can be replaced but is difficult to order.

The E39 M5 was launched with Motorsport's first V8. A 4.9 called the S62. It developed 400bhp and was well regarded. It's only real problems are it's thirst for both petrol, rather expensive oil and clutches. An 850CSi clutch is a good upgrade apparently. The S62 was also used in the Z8 roadster.

The E46 M3 had to improve on the E36 M3, not an easy task. The S52 became the S54 and discplacement grew to 3.4 litres with 343bhp. For the lightweight M3 CSL with it's carbon fibre airbox 360bhp was possible. But this was really stretching things. The six cylinder engine wasn't going to go further than this, a V8 would be needed for the next M3.

BMW's Formula One involvement gave birth to a 5.0 V10 for the E60 M5. The S85 made 400bhp in normal use or 507 once the M button on the steering wheel was pressed to unleash it. It also saw use in the E63 M6. It truly was a beast of an engine and was coupled to a seven speed SMG gearbox, except in America where purists rightly demanded the option of a six speed true manual gearbox.

The 2008 M3 took the S82 V10, lopped off two cylinders and called it the S65 4.0. Unlike the V10 the V8 had a wet sump. It produced 420bhp at a screaming 8300rpm.

Modified engines

Modified engines shouldn't necessarily be avoided if done by a reputable company. An engine which has been taken to bits are put back together with new gaskets could save money in the long run. This is particularly true of the M42 1.8 16 valve engine with its infamous profile gasket problem.On the other hand an engine producing power far in excess of its design parameters will over stress components and cause premature failure.

Engines from tuners such as Alpina, Hartge and AC Schnitzer improve on the factory design in several ways.