M10

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The BMW M10 is a 4-cylinder engine, fitted to the E30 from its 1982 launch until 1987.

M10B18 fuel-injected engine
M10B18 fuel-injected engine

Contents

History

The M10 engine as seen under the bonnet of an E30 is the culmination of a design that goes all the way back to 1961. Its conception began when engineering and racing hero Baron Alex von Falkenhausen was asked to design a small-displacement 1.3 litre engine for BMW's new line-up. Von Falkenhausen had the foresight to realise that not only was the specification too small, but also that increasingly larger capacities would be needed in the near future. To that end, he put forward a design that started at 1.5 litres, but which could easily be expanded to 2.0 litres to meet the company's future needs.

Over the next decades, this engine went through a large number of permutations, proving its capabilities with twin-carburettors, fuel injection and even turbos. Factory-produced 2-litre turbos powered the BMW 2002ti to 170hp, while racing versions reached over 1000hp. In all, over 3.5 million units were produced, powering various BMW models for over 25 years.

At the end of 1982 with the release of the E30, a 1.8 litre carburreted version was fitted to the base model 316 and a fuel-injected version powered the 318i. A smaller 1.6litre carburreted engine from the E21 was exported to Greece and Yugoslavia as the rare 316s. These models comprised the 4-cylinder range of E30 engines alongside the M20-powered 320i and 323i. To compliment BMW's range, the 1.8 engine would be fitted to the 5-series E28.

The M10 continued through the E30's September 1987 facelift. The 316 continued on, while the fuel-injected M10 was rebadged as the 316i, freeing up the 318i name for the new M40 engine. But after just one year the 316 was dropped and the 316i received a smaller M40 engine, removing the M10 engine from the E30 range in September 1988.

However, this was not the end of the E30's relationship with the M10. In September 1986, the S14 engine was fitted to the first M3. Based upon the M10 block, this engine would be pushed to 2.5l during its lifetime, with the final 1991 models achieving 235hp.

M10 engines are still highly sought after for classic racers and performance enthusiasts, as their simple solid construction makes them ideal for performance upgrades compared to later engines.

Versions

Models
EngineDisplacementPowerTorqueRedlineYear
M10B181.6 L (1766 cc/97 in³)89 hp (66 kW) @ 5500101 ft·lbf (137 N·m) @ 400062001982-1987
M10B181.8 L (1776 cc/109 in³)105 hp (77 kW) @ 5800107 ft·lbf (145 N·m) @ 450062001987

While identical in engine construction, the two versions differ in their fuelling and engine management setups. While the more powerful version featured Jetronic fuel injection to increase output and fuel economy, the lower-powered unit uses a simple carburettor and mechanical distributor; this would be upgraded to an electronically-controlled carburettor in 1984 which is a common problem.

All M10 engines use a timing chain.

Components

The engine in all E30s is a three-part design, featuring a cast-iron Block with a steel Sump at the bottom and an aluminium Head at the top.

Sump

The M10 Sump is a two part design with an upper and lower sump. The upper part bolts directly to the block, sealed with a gasket, and the lower sump then bolts to the upper.

Leaks in this area are normally due to upper bolts coming loose, despite their torque rating. Because some of these bolts are only accessible with the lower sump removed, the two parts have to be disassembled to cure the leak. When removing the lower sump, don't be surprised to find a bolt sitting in the oil that has come out completely from the upper sump.

Damage is also a problem. The M10 cast aluminium construction makes the sump prone to cracks and holes when hit, and no other E30 sump is compatible.

Oil Pump

The oil pump is chain-driven from an independent sprocket on the crankshaft. It is a gerotor pump (one cog inside another). It is bolted to the front centre of the engine block, and is supplied with oil via a pick-up tube into the sump.

The M10 pump is relatively simple to replace. Just unbolt the drive gear from the pump, and then unbolt the pump from the block.

Block

A single block design was used for all M10 engines, and they are completely interchangeable between models. All blocks use an 89mm centre bore.

Bear in mind that although the M10 engine was also fitted to a large number of other engines. For that reason, although the blocks themselves are the same design, different bores were used to vary the capacity of each engine. The absolute maximum bore size is 94mm, but the safe limit is 93mm.

Crankshaft

While the block determines the maximum capacity for the engine, the crankshaft determines the stroke of the engine, and therefore the actual displacement. Mounted to the bottom of the block, the crank holds the bottom of the piston rods and converts their up/down motion into rotary force known as torque. It does this by holding the rods on a series of lobes or 'throws' which extend away from the centre of the crank by a certain distance.

The M10 crank is a cast-iron unit with a 71mm stroke. However, it is possible to increase this using the S14 crank to up to 87mm.

Piston Rods

All M10 engines use the same 135mm piston rods.

Pistons

The M10B18 used the same piston design throughout its use in the E30. However, M30 pistons are also compatible.

M10B18 9:1
82-88
Ø: 89
KH: 47.1
ÜH: 4.5
GL: 83.6
BO: 22.0 x 58
Stroke: 71
Conrod Length: 135
Volume 1766cc
Piston Shape:
Measurements (mm) Image:dimensions_mahle.jpg
Definitions Ø: Diameter of piston KH: Distance from center of wristpin bore to top of piston top ÜH: Height of piston crown over piston top plane VT: Depth of depression in piston crown MT: Depth of depression in piston top GL: Total length of piston BO: Bore (and length) of wristpin

Timing Chain

The M10 uses a chain to drive the valvetrain (unlike the M20 and M40 engines). Therefore, a sprocket is mounted at the end of the crankshaft to power the chain, which drives a corresponding sprocket on the camshaft. Most people feel that chains are indestructible, but it is recommended to replace the tensioner every 100,000 miles. In the event of a noisy chain, replacing the chain tensioner should quieten things down.

Learn more about changing the timing chain tensioner.

Head

The 8V cylinder head on all M10 engines is a cast aluminium unit, and significantly differs between carb and injection models. While the obvious difference is whether there are holes for the injectors, there is also the issue of port shape which makes the heads incompatible.

Unfortunately, the head is the weak part of the M10 engine. they are susceptible to cracking when overheating. The only way to check is to remove the head.

Rocker Cover

It is positioned on top of the head with 8 collar screws. It has one hole for the Oil Cap, and one port for the breather hose.

When removing and replacing the rocker cover, it is worth replacing the rocker cover gasket.

Cam

On the M10, an overhead camshaft drives the intake and exhaust valves via rocker arms. This camshaft is chain-driven, and held in place using 3 bearings. It is lubricated by an overhead oil spray bar. The rear end of the cam features the gearing to power the distributor.

All engines use the same cam, which is also compatible with the E21 engine.

Valves

Being an 8-valve engine, the M10 head contains one intake and one exhaust valve per cylinder. Valves were different between carbed and injected engines:

316: 42mm intake, 35mm exhaust 316i/318i: 46mm intake, 38mm exhaust

All engines use an 8mm stem.

Valve tappet clearance, inlet and exhaust on a cold engine: 0,20mm

Valve tappet clearance, inlet and exhaust on a warm engine: 0,25mm


Rocker Arms

The valves are opened and closed by rocker arms, which are pressed on by the cam. These rocker arms perform a dual function of cam follower and valve adjuster, as one end contains the eccentric and the adjustment nut. The rocker arms pivot around rocker arm shafts.

Head Gasket

The Head gasket forms a seal between the Head and the Block, maintaining compression in the cylinder while keeping the Oil and coolant separate. Any failure in the head gasket will cause a drop in engine power, and will also lead to mixing of the oil and coolant, known as mayonnaise.

To diagnose a broken Head gasket, look for a creamy substance underneath the oil filler cap. If present, remove your dipstick and look at the oil. If it resembles milky coffee, then it is very likely your head gasket has failed.

In the event of a failed gasket, it is important to check the condition of the head; more severe damage may have been done, including cracking of the metal which will render the head useless.

Learn more about changing the head gasket.

Breather Hose

To balance the pressure inside the head, a rubber hose runs from the top of the rocker cover to the throttle body or air filter, depending on engine version.

Ancilliaries

Flywheel

The M10 flywheel is a single mass wheel which keeps the engine spinning long after you take your foot off the throttle. It is also the flat surface to which the clutch mates, ultimately transferring power from the engine to the Drivetrain. The edge of the flywheel is toothed. Known as the ring gear, it is what allows the starter motor to bite onto the engine to start it. The flywheel bolts to a pulley at the end of the crank.

For manual engines, the flywheel contains a spigot bearing to centre the input shaft of the gearbox to the tail of the crankshaft. These parts are essential when converting from auto to manual. For automatic cars, the flywheel is little more than a ring gear with a plate to which the torque converter is bolted.

Starter Motor

The starter motor is a standard 1.4kW motor with a bendix engagement wheel. It is an all-in-one unit containing motor, solenoid and relay. When activated, the starter gear extends to meet the flywheel and then spins, driving the engine.

All M10 starters are interchangeable.

The starter is wired directly to the Battery + terminal and the alternator. A smaller connection, fed by a black/yellow wire, is the incoming signal from the ignition switch. On facelift vehicles there is also a black/green wire to load reduction relays.

Engine Mounts

M10 engine mounts are the standard design of aluminium arms cushioned with rubber mounts. On some models a hydraulic shock absorber was also fitted to provide superior vibration damping.

If you are taking an engine from an E21 or E28, you will need E30 engine mounts.

Servicing

Main article: Basic M10 Servicing

Every engine needs its fluids and filters changed regularly. The M10 timing chain tensioner will also needs its timing chain replaced after a certain mileage. If yours is getting rattly, learn more about changing the timing chain tensioner.

Common Problems

While the M10 was a sturdy engine, it does wear down and all surviving E30 units will be over 25 years old now. Therefore, most will be suffering from some form of engine wear to the point of requiring a full rebuild.

Carburettor Upgrade

The Pierburg 2BE carburettor found in most 316 models is not considered a particularly good carburettor. Converting to a Weber carburettor will yield more power and more tuning options. Learn more about Weber carburettors.

Common Upgrades

The M10 is an incredibly tunable engine; BMW's racing division achieved 1350hp from the unit in 1986. The possibilities are pretty much endless, with twin-carb setups, stroker engines and turbo-charging all common features among M10 modifiers.

A lot of modifying involves stroking the engine with components from the S14 engine; specifically the crankshaft and piston rods.

Useful websites

See also