BMW Buyers Checklist - Engines and their History
Some engines are better than others. In the USA there is less choice as they don't get many of the smaller engines, but elsewhere 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.
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 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 / M44 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 maintenance. I just can't say enough good things about these engines. The M44 is my engine of choice in a Z3.
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. Any car you're buying today has likely had this fixed years ago.
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 enhanced N43 and N46 variants. The N43 features direct injection, because of this it wasn't sold much outside of europe due to fuel sulphur content issues.
These are generally good engines although the N42 had a habit of stretching the timing chain and being prone to oil leaks.
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 E90 homologation special. The N45 replaced Valvetronic with a normal throttle body, this worked better at very high engine speeds and in the 2.0 E90 320iS racing homologation version it produced 173bhp at 7000rpm.
Valvetronic is of not of much benefit to supercharged or turbo changed (such as turbo-diesel) engines. The lower intake restriction isn't an issue with forced induction, but Valvetronic does give quicker throttle response.
In 2011 BMW introduced the N20, confusingly the numbers were going down instead of up now! Most N20s were two litre although there was a seldom used 1.6. The N20 had a heavy burden on it's shoulders, its job was to replace the straight six engines beloved of all right thinking BMW enthusiasts! To do this it used turbocharging, the amount of boost and other minor changes made the difference between a 320i and a 328i with no difference in engine displacement. Sad days, but the changes were a result of new emissions legislation and the search for improved economy.
Power would rise to an impressive 241bhp accompanied by 258 lb/ft of torque. The turbo meant a hefty delivery of torque all through the rev range, good in many ways but part of the fun with older BMWs was having to drive them right in order to get the best power delivery. They were generally reliable engines so long as they weren't neglected. They only saw four years of service before being replaced, that wasn't a reflect on the N20 but on BMW's new "modular engine" strategy (see section below).
BMW's smallest cars shared the N13 / N18 engine with the MINI from 2011 until 2015. This was developed in conjunction with Peugeot and comes from their heritage. BMW brought Valvetronic and all their latest technologies to the party. All BMW versions had a turbo.
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 and that's no bad thing. 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 for their size. Biggest fault is worn camshafts due to loose oil bar bolts or owners letting the oil level drop too far too often. The M30 was an epic engine, it felt like the heart of the car and the accelerator was there mainly to limit its power, not to demand even more. In manual car it was totally addictive.
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 octane 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!
Alpina had a field day with the M30. Even in normally aspirated form an E34 B10 made 265bhp, for a two valve per cylinder engine that only tells part of the story. My 1989 B10 even had an electronic throttle body from the M70 V12 to enable the traction control. For those with left hand drive a fearsome turbo B10 was available and could reach 188mph.
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. It killed the clutch on the first dyno run.
In parallel with the M30 the N"little six" M20 (initially called M60) 2.0, 2.3, 2.5 and 2.7s were launched in 1979 and ran until the early 90s. These were used in the older E30 three series, E28 520i and 525e / 528e and early E34 five series. They were 12 valve belt driven engines with a good reputation. M20s had 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 fewer camshaft bearings, weaker valve springs and longer intake runners. They are sometimes used as the basis for 2.7 litre stroker 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 (except for the USA), something which caused a lot of problems for users in areas with high sulphur fuel. The M52TU solved this in March 98. The TU also replaced the single VANOS variable valve timing 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 re-chip 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. I find my M54B25 revs much more sweetly than my old M52B28.
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 is 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. The only down side is that direct injection can cause carbon deposits to build on the back of the intake valves as there's no fuel to wash them clean. They may need manual cleaning every 40,000 miles.
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 bhp - unmodified! The N54 was replaced by a single turbo N55, this used a large twin scroll whereby the exhaust gases enter at two angles to reduce the lag associated with big turbos.
Here began the Dark Ages in 2011, the period where the N20 turbo four cylinder replaced most sixes. But the dawn of the modular B58 in the 2015 340i (a three litre turbo car, not a four) brought with it a new six. Sadly the mid-range cars would still have a four cylinder or even a three!
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 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. It drove well and any other manufacturer would have been proud of it. Once the sulphur issue was sorted out it became a durable and well liked engine.
Subsequent M62 3.5 and 4.4 units had improved cylinder liners to avoid the problem. The M62 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. An M62TU appeared in 1998 with an electronic throttle body and a slightly improved power spread.
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. It had VANOS on all four camshafts and an electronic throttle body. Many design features were common to the N73 V12 which was in effect a longer N62.
In 2008 the N63 was announced for the new X6. This was a new reverse flow V8! Twin turbos were fitted in the V8 valley with intakes at the sides to improve packaging. A very novel concept producing over 400bhp and 450lb/ft of torque. BMW had a raft of technical problems with this engine, some caused by poor quality parts. The poor project head for this engine must have been in despair as the issues mounted. BMW USA had to work very hard to keep customers faithful in light of this and it cost them a bucket of money.
V12 Petrol Engines
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 S70/2 based V12 for use in the McLaren F1.
The M70 was replaced by a 5.4 litre M73. This carried on using two valves per cylinder and moving part distributors (one per bank) long after other BMWs had moved on.
It was replaced by the all new N73 6.0 Valvetronic V12 in 2003 for the E65 750Li. This was a much more modern engine, made possible by being designed as a longer version of the N63 V8. In 2009 it was replaced by the turbocharged N74 in 6.0 and huge 6.6 capacities, the latter monster destined only for Rolls Royce owners.
BMW make the smoothest diesel engines in the world, no question! But if you're thinking of buying a diesel BMW check out the petrol vs diesel page first.
The M21 was a diesel version of the M20 six, it was used on the 1983 E28 524td 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 motor home. Laster versions were the first BMW engines to use a fly by wire electronic throttle body.
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 1999 introduction of the M47 2.0 four and M57 six cylinder engines in the late 90s. Both are advanced four valve per cylinder 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 made a V8 diesel using the same technology, the M67 in 3.9 and 4.4 versions. It was never sold in the UK.
For 2006 a new range of diesels emerged, the N47 four and N57 six (no V8 this time). These were the first aluminium block diesels, a feat accomplished with the aid of iron cylinder liners and large stiffening webs in the lower engine.
The N47 used twin balancer shafts for smoother running whilst at the other end of the scale the N57S had three turbos and produced 276 bhp and a stump pulling 550 lb/ft or torque.
BMW had built the timing chain at the rear of the engine, supposedly to ease packing of ancillaries at the front. They'd also machined the crank sprocket directly onto the crankshaft, a first. These changes really came home to roost. The crank sprocket design made many chains wear and stretch, a major problem. Replacement involved removing the engine from the car and fitting a new crankshaft, a nightmare scenario.
From 2015 the diesels became part of the modular engine series, see below.
M-Tech engines are superbly engineered and normally hand built. They can take the pressures of sustained high speed or track use but must be properly maintained. 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 is done by means of 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 M42 based 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 closer 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 save 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 S50B32 producing 321bhp. It's VANOS gear had seals which hardened over time and eventually need to be replaced with those of a better design, not a cheap procedure. It also has a VANOS oil filter which should be replaced at every oil change but seldom is.
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 S50B32 became the S54 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 S85 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.
In 2010 BMW launched hot version of the X5 and X6 with a Motorsport S63 V8 engine. This was based on the problematic N63 but the Motorsport version seems to be more robust and solve many of the lesser versions problems. The S63 was a 4.4 twin turbo, like the N63 it was reverse flow and the exhaust driven turbos lived in the valley between the two cylinder banks. Never let it be said BMW designers can't think outside of the box. In 2011 the engine saw minor revisions and powered the new F10 M5 and F12 M6. Final versions made 567 bhp.
2014 saw the introduction of the S55 three litre straight six twin turbo, it powered the F80 M3 and F82 M4. Whilst it was based on the S55 it underwent significant reworking by the mad scientists and had many upgrades. It can rev to 7600 rpm and makes 425 bhp, 137 bhp per litre. Water to air intercoolers were used instead of normal air to air intercoolers, this was judged to be more efficient both thermally and in packaging terms. It needed twin high pressure fuel pumps to cope with demand.
B58 showing unusual split timing chain with idler.
The New Modular Engines - BMW's Brave New World
In 2014 BMW began to replace all of it's petrol and diesel engines with the new modular series. These were based around the concept of 500cc cylinders using similar technologies on three, four and six cylinder blocks. Capacities would be 1500, 2000 and 3000cc.
The programmes two main goals were lower manufacturing costs and compliance with increasingly stringent EU emissions directives. All engines can be made on the same production line, it's in Steyr Austria and has a capacity of 5500 units per day.
The four valve per cylinder engines are all alloy (even the diesels) and have double VANOS, the newest fast Valvetronic throttle mechanism and direct fuel injection. The timing chains are at the rear of the engine and use an idler gear to transfer power. All have water to air intercoolers built into the inlet manifold. These are a world away from the M10!
The three cylinder units have single scroll turbos, the fours and sixes have twin scroll turbos. On the latter half the cylinders exhaust onto the upper section of the turbine and half on the lower. This reduces turbo lag but still produces high turbine torque to compress the inlet air. They run up to 26psi boost, which is very high. Fuel injection pressures can rise to 2000 bar (29,400psi).
They're designed to be compatible with BMW's Efficient Dynamics and start / stop technologies for lower emissions in city traffic and even have "on demand" water and oil pumps. Some have both mechanical and electrical coolant pumps, the turbo having a dedicated unit.
All engines have top and side covers, up to six for the larger sizes. Not only are these designed to reflect noise back into the engine but they thermally insulate the block. This leads to and engine that warms up faster and retains heat, overnight it may be 10C warmer.
So this is the future, driven by the quests for higher power combined with good economy and emissions levels that comply with EU6 and beyond. Overly complex, perhaps. A mechanics nightmare, possibly. But as usual BMW is leading the way in engine design and the modular generation is the only possible response to the requirements of customers and future legislation.
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. 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.