Overall, though, the M10 is a very good engine, but it demands regular maintenance
Engine in focus This month we spotlight the influential and long-lived M10 range of four-cylinder petrol engines
WHAT CARS, WHICH M10 ENGINE?
1600, 1600Ti, 1502, 1602, E21 315, 316
1800, 1800Ti, 1800 TiSa
1800 from 1966, 1800Ti, 1802, E21 318, E30 318i, E12 and E28 518 and 518i
2000, 2000Ti, 2000Tii, 2000CS, 2000C, 2002, 2002Ti, 2002Tii, E21 320, E21 320i, E12 520, E12 520i
You could say that there are two BMW companies, the original firm that made the 328 and ended with the last V8 cars such as the Baroque Angel and 3200CS, and the ‘new’ BMW that began under the Quandt family and the New Class 1500 in 1961. You’d probably be right because the 1500 marked a complete change of direction for BMW, going from hand-built, expensive monsters that didn’t sell very well – and dead-ends like the 700 and Isetta – to a new class of car that led to BMW being where they are today.
The 1500 was announced in 1961, went on sale in 1962 and became Germany’s Alfa Romeo; a compact, four-door with excellent handling and performance, as well as very good build quality.
At the heart of the Neue Klasse was an all-new engine, a neat OHC, four-cylinder unit designed by Alex Von Falkenhausen, a BMW veteran who’d been with BMW since before World War 2.
In 1961, engine technology was like this; British firms were turning out all-iron OHV units, such as the BMC B Series, with a 1,500cc unit developing 50-60hp.
Rootes and Ford also made similar engines with similar power outputs. A 1600 MGA with twin SU carburettors, developed a claimed 79hp, although the British motor industry wasn’t averse to bumping-up power figures in those days! For example, an MG Magnette saloon struggled to 60mph, taking nearly 20 seconds, while the BMW 1500 with a DIN-certified 80hp, did the same thing in 15 seconds – go figure!
The 1500 engine – coded M10 – was an all-new design taking nothing from previous BMW motors. An iron block provided the base, with 82mm bores, and the crankshaft was a forged-steel job with five main bearings and a stroke of 71mm, giving a capacity of 1,499cc.
The cylinder head was an alloy crossflow casting, with big ports and valves, hemi combustion chambers, inclined valves and one camshaft operating all eight valves via rockers on two rocker shafts – one for exhaust and one for inlet. The cam was driven by a Duplex chain with a simple rail one side, and a tensioner blade on the other, with a plunger that was both spring-loaded and oil pressure-driven.
On very early models (until around late 1963, unless you know different), BMW used a spring-loaded idler gear, but this was replaced by the curved slipper rail we all know and love. I’ve no idea why this happened – perhaps due to cost or even reliability issues, but you’ll be very lucky to find one now.
The oil pump was bolted to the front of the block and driven by a short chain from the crank sprocket. It sat in the front sump bulge and delivered filtered oil in the normal way to the camshaft lobes via a steel spray bar – a tube with holes in it that sprays oil between two lobes and gets enough on both of them.
The distributor sat at the back of the head, and was driven from a cam gear. Carburation on the 1500 was provided by a single-choke Solex 34PCIB, and the power output was that previously-quoted 80hp at 5,700rpm, accompanied by 118Nm of torque at 3,000rpm on an 8.8:1 compression.
February 1962 saw the 1500 enter production, and the next logical step was a bigger-engined version, the 1800. It’s not known if that chain tensioner gear made it this far, but the 1800 began production in September 1963.
The M10 was given an overbore to 84mm, while the 1500’s 71mm stroke crank was lengthened to 80mm. With timing alterations and a 36/40 PDSI Solex carburettor (also fi tted to the 1500 for 1964), the 1800 delivered 90hp DIN at a low 5,250rpm. Despite the ‘36/40’ bit, this was not a twin-choke carburettor.
The capacity of the 1800 was 1,773cc, and the torque output was 134Nm at 3,000rpm on an 8.6:1 compression ratio.
Things came to an end for the 1500 in 1964, and it was replaced by the new 1600 model. The extra 100cc of capacity was achieved by making the bore 3mm larger, and using the 1800’s 84mm block. This both saved BMW money and improved the teething problems that had been seen on the 1500 – there was talk of connecting rod failures on some engines, and the revised M10/M30 con rod was like something Brunel might have designed. The 1600 boasted 85hp at 5,800rpm and, with an 8.6:1 compression ratio, produced 123Nm of torque at the usual 3,000rpm.
The 1800Ti was also launched in 1964; BMW’s go-faster version. The 1800 unit was revised with bigger valves, a pair of Solex 40PHH side-draught carbs, plus a diff erent cam and exhaust. Power was rated at 108hp at 5,800rpm, paired with 148Nm of torque at 3,800rpm and a higher, 9.5:1, compression ratio.
An 11-second 0-60 time was right up there with the Lotus Cortina and Mini Cooper S, and a special SA (Sonder Ausfuehrung or special version) 1800 TiSA arrived in 1964, to homologate a few trick bits for racing. Thanks to the addition of 45 DCOE Weber carburettors, a longer duration cam and a high 10.5:1 compression ratio, this unit delivered 128hp at 6,100rpm together with a very peaky 157Nm at over 5,100rpm. The special model’s maximum speed was recorded at 116mph, and the car could sprint to 60mph in nine seconds – serious ‘go’ for 1964.
This both saved BMW money and improved the teething problems that had been seen on the 1500
M10 pre-1980 cam, rockers and chain. An M10’s bare head – simple engineering. The 1962 BMW 1500, which saw the first use of the four-cylinder M10 petrol engine, in this case in 1,499cc form.
In 1965, the 2000 M10 unit made its debut in the new 2000CS Coupé. The 1,990cc capacity was achieved with an 89mm bore and an 80mm stroke. There was a ‘cooking’ version with an 8.5:1 compression ratio and single Solex 40PDSI carburettor that produced a solid 100hp at 5,500rpm, coupled with 156Nm of torque at 3,000rpm. This engine was fitted to the automatic 2000C, while the 2000CS (manual only) got the full-fat, twin-carb version of the engine. This was fitted with a pair of 40PHH Solexes (from the 1800 Ti) and ran with a compression ratio of 9.3:1. The result was 120hp at 5,600 rpm and 167Nm of torque at 3,500rpm.
This was enough output to give the 2000CS useful performance, with a top speed of 110mph and a 10.4-second 0-60 time – faster than a Rover 2000TC. The 2000 engine in both single- and twin-carburettor form, went on to be fitted to the New Class saloon in 1966, and the 2002 in 1968, but there was more in the meantime.
For 1966, the 1800 engine was revised. To reduce production costs, the 1800 made use of the 89mm bore block from the 2000 engine, plus the 71mm-stroke crank from the 1600. This resulted in a new capacity of 1,766cc, although the quoted power output remained the same. However, the new engine was smoother at high revs, thanks to its shorter stroke. BMW also launched the two-door 1600 in 1966, and added a 1600Ti version; a very sparkly version with the same modifications as the 1800Ti, resulting in a lively car befitting its 105hp at 6,000rpm and 131Nm at 4,500rpm figures. A 10.8-second 0-60 time and 110mph top speed made the 1600Ti a fast car that was very popular in the USA – like a well-made and reliable Lotus Cortina!
In 1969, a 2000Tii was launched with Kugelfischer mechanical fuel injection, which gave the 2000 great performance as you’d expect, with 130hp and 176Nm of torque and a sensibly-high 9.5:1 compression ratio.
The 121 cylinder head was introduced with the 2000 engine, and filtered its way on to the other M10 units thereafter. The M10 then continued in this form until autumn 1972, by which time the New Class was about to be replaced by the E12 520 and 520i. This first 5 Series used the M10 2-litre engine, but with changes.
The 520 used a pair of Stromberg 175CDET carburettors plus a new design of combustion chamber and piston crown, and this unit developed 113hp at 5,800 rpm. It produced a torque figure of 165Nm at 3,700rpm with a 9.1 compression, and this unit was used only in the 520 – the E12-type engine, with its new head (with ‘E12’ cast on the side), was used in the 2002 from late 1972, but only the 520 used this bizarre, twin-carb set-up. The 520i relied on a revised version of the 2002Tii unit, with the new E12 head, but the power outputs were virtually identical.
BMW launched a 518 E12 model in 1974, in the wake of the fuel crisis. It was an 89hp rocket-ship (not) version of the 520 fitted with a detuned, 1,766cc engine.
Running a single-choke Solex 32/32 DIDTA carb and a low, 8.3:1 compression ratio, that 89hp was achieved at 5,800rpm together with a fair, 140Nm of torque at 3,700rpm. But BMW soon revised this simply because the 518 was so slow. Consequently, a twin-choke Solex carb was fitted from late 1975, but there are no power figures for this.
At the opposite end of the scale from the 518 was the 2002 Turbo. Based on a Tii motor, the Turbo’s engine used a KKK turbo, a different version of the 121 head (with machined chambers), dished pistons and various other details that mean not much directly interchanges. Power was rated at 167hp at 5,800rpm while torque was 240Nm at 4,000 rpm on a low 6.9:1 compression ratio.
The 2002 Turbo made use of early turbo technology, and had the first, small- capacity turbo engine that made it into production. In retrospect, the truth is that it wasn’t very good, suffering as it did with chronic lag and reliability issues that should have put people off turbos for life. However, when properly set-up, it was pretty fast and exciting car to drive. But it was Saab who really took the bull by the horns, developing the turbo-charged four-cylinder into something reliable, easy to drive and economical.
In 1975, the 2002 range was replaced by the new E21 3 Series, which brought with it another raft of revisions. The engine’s head was again revised (coded ‘E21’ on the side), but the biggest change was in the fuelling system. Gone was Kugelfisher mechanical injection and in came Bosch K Jetronic, which was fitted to the new 320i as well as the existing 520i models.
The 316 used a revised version of the outgoing 1602 engine, with 89hp and 123Nm, while the 320 got a new two-litre, producing 110hp and 152Nm on a low 8.1:1 compression ratio. The two-litre M10 ceased production in 1977, as the new M60 (later M20) two-litre straight-six engine was fitted to the 320 and 520, leaving the 1,600 and 1,800 units in the 316, 318 and 518 cars.
September 1980 saw the end of the 1,600cc engine in the 316, when it was replaced by the 1,800cc. There was also a change to the timing chain setup on all M10s. The original Duplex chain was replaced by a lighter but equally robust Simplex chain and, at this time, the distributor was altered to run in the opposite direction (anticlockwise).
There was a base 315, fitted with a Pierburg carburettor, that produced 75hp and 110Nm of torque, but this wasn’t imported into the UK.
The new 1,800cc 316 gave 90hp and 140Nm on a 9.5:1 compression with a Solex Pierburg 2B4 twin-choke carb and, once the 315 had been discontinued, this 1,800cc unit was one of only two M10 engines left in production. It powered the 518 in E12 and E28 bodies, and was made alongside the fuel-injected version.
The first one used Bosch K Jetronic until late 1982 and the end of E21 production, and this had 105hp and 145Nm of torque – this engine would be used in the early E30 318i. For late 1983, the E30 318i and 518i (not sold in the UK until 1985), had a new version of the M10, with yet another revised cylinder head for emissions and Bosch LE Jetronic fuel injection. Power figures were as before (well, 103hp) on a high 10:1 compression ratio.
By now, the M10’s successor – the M40 – was at the design stage, and the M10 was over 20 years old. The first M40 engine was built in mid-1987, for the launch of the facelifted, plastic-bumper E30 and the final E28 518i, built in December. The M10 continued for another few months until July 1988, when the final M10-engined car was built, an E30 316 that was replaced by a 1,600cc M40 316i.
The M10 had been in production for 25 years, yet had barely changed, such was the quality of the original design. However, by 1980s standards, it was heavy, not very good on fuel and engines such as the GM Family 2 were probably better all-rounders by then. What’s more, the M40 was certainly a better unit and a worthy replacement.
This both saved BMW money and improved the teething problems that had been seen on the 1500
M10 BMW 2,000cc
M10 LE Jetronic fuel injection.
The M10 cylinder block.
M10 520 Stromberg carburettors.
M10 DIDTA Solex carburettor.
M10 head type number location.
M10 2002Tii engine.
An M10’s bare head – simple engineering.
M10 E30 318i head casting.
WHAT GOES WRONG?
The M10 relies on the kind of maintenance that modern engines don’t need. It has manual-adjust tappets that need doing every year or 12,000 miles, and the cam spray bar needs to be cleaned out – remove the banjo bolts, twist it through 180° and run a small drill through the oil holes to open them up a bit. Fit new banjo bolts from BMW as well – the originals always had a habit of coming loose and the new ones have a slightly different thread pitch so they stay in place.
Never ever thread-lock the old ones into place as the stuff will just congeal in the oil hole. The post-1980 Simplex timing chain was very strong, but it has a habit of wearing out the camshaft sprocket. But you can buy these new and they’re simple to fit.
Head gasket trouble is rare, but cracked heads and popped exhaust manifold studs aren’t. The inlet side of the LE Jet injection engines is a swine to work on, and be very careful about swapping cylinder heads – you need the right head for the right pistons and, on the E30, the 318i and 316 heads are different.
Overall, though, the M10 is a very good engine, but it demands regular maintenance. However, it was never quite as bulletproof as some claim, and many were very tired by 100,000 miles, and showing signs of valve guide and cam wear. Low oil pressure can be a problem – you may find it takes ages for the oil pressure light to go out. This can be an O-ring on the pipe from the pump to the block that’s blown out on a cold start, but it’s not too bad to lower the sump slightly and remove the timing chain cover to replace it.