M42

An engine found in all E30 318iS cars and some early E36 cars.

Often referred to as an Engine crafted by God Himself..

In E30 form it's twin cam 16v 4cyl 1796cc engine. It is a aluminium alloy engine which has a relationship with the M1, M5 and M635CSi engines. The top of the rocker cover has a vapour/liquid separator which reduces oil consumption of the engine and bi-concave combustion chambers. Both very good examples why the M42 was state of the art at the time of production. The engine also has a duplex timing chain and a compression ratio of 10:1, which is similar to the duplex chain E30 M3 with a compression ratio of 10:5. The throttle body has two butterfly valves, a 35mm and 54mm valve. When you are lightly pressing the accelerator pedal, only the smaller valve opens but when you further depress your pedal the larger valve also opens. This enables the M42 engine to use less petrol when the car is on journeys which do not require constant change in speed. The inlet manifold is in two pieces, its design improves the low down torque of the engine. The engine also has hydraulic tappets which reduce the maintence of the engine. On every cylinder there is a coil pack which can be seen in the photo below (black item inside the wing next to the washer bottle) and is run on the Bosch Motronic injection system. The engine produces 136BHP at 6000RPM and 127 ft lbs of torque at 4600RPM, but the engine was then superceeded by the M44.

The E36 version adds a serpentine belt front pulley system and a different intake manifold. The M44 engine after 1995 was a 1900cc engine which produced 140BHP with 129 ft·lbf of torque and had a lowered redline of 6300RPM which is most commonly found in the E36 318iS

M42B18 Engine as fitted to an E30 318is:

Identifying traits and points of interest in the above photo:

• Individual coil packs
• Twin-cam rocker cover
• Twin-choke throttle (not-visible)

Common Problems

The Profile Gasket

The most common problem with the 318iS was the profile gasket failing on the engine. The chemicals in the coolant would deteriorate the gasket until it failed. The repair for this job is extensive (cylinder head, radiator, thermo-fan, crank pulleys and the front timing chain covers are just a few components that had to be removed). The gasket would normally fail around the 50,000 miles mark and wasn't always covered under the warrenty.

Gasket(x1): 111 217 215 46

Bolt set(x1): 111 217 219 39

Valve cover (x1): 111 217 218 76

Valve cover (x1): 111 217 214 76

Valve cover (x3): 111 217 214 75

Gasket (x1): 111 412 478 49

Gasket (x1): 111 412 478 37

o-ring (x1): 121 417 272 20

seal ring (x1): 071 199 633 55

Gasket (x1):116 117 344 90

Gasket (x1):116 1173 468 4

o-ring (x1):115 3172 121 8

Gasket (x1):115 3172 117 2

antifreeze (x1): 821 414 677 04

Throttle-b (x2): 135 412 474 00

Gasket (x1): 183 017 119 69

Nut (x4): 183 017 377 74

Gasket set (x1): 111 417 219 19

The Timing Chain Tensioner

The symptoms of a wearing tensioner is a rattling noise coming from the front of the engine which can easily be heard in the car from around 2000-3500rpm. It is a simple and relatively cheap fix, simply take the old one out and insert the new one. However, you can also re-fit an M44 tensioner. It is recommended that you change the tensior as soon as possible when the sytpoms begin to occur; a worn tensioner will cause the timing chains to stretch resulting in in new cam chain sprockets, timing chains, guides and various gaskets and can cost in the region of £550 (including labour from a specialist).

Timing Chain tensioner part (x1): 113 117 431 87

Timing Chain tensioner washer part(x1): 071 199 633 55

Tapping/ticking noise

When most people hear a ticking engine they instantly believe that the tappets are worn. This is not always the case, sometimes it can be a crack in the exhaust manifold. Normally the ticking will go away once the car has been driven for a while, so people believe tht the oil has reached operating temperature and cured the tapping problem. However, it could be a small hole in the exhaust manifold that is sealed when the manifold gets hot (ie expanding metal covering the hole up!). This is most common on cylinder one.

Fuel smell

Some times you can smell petrol fumes on startup, which can smell alot worse if you turn on your fans. This can be a small fuel pipe just behind the inlet manifold which can perish or sometimes just needs the jubilee clip tightening. Petrol cannot always been seen (unless the engine is cold) as the petrol instantly evaporates from the heat of the engine. But you should see the leak leaking onto the fuel rail trim and down the fuel inlet and return pipes for the engine.

Lumpy idle

The m42 engine is prone to the air breather pipes perishing. This results in unwillingness to start on cold mornings and a lumpy uneven idle. If you open the bonnet with the engine running you may be able to hear a hissing sound. Then all you need to play is hunt the sound considering there are alot of breather pipes to the engine. If there is no hissing sound it could be the valve in the idle control valve (ICV) sticking. Simply disconnect the ICV by undoing the jubilee clips (its found between the engine and bulkhead on the passenger side and is a "T" shape) and spray some carburettor cleaner into the valve. This should stop the valve from sticking, or you could replace the ICV completly.

Common upgrades

Most people instantly buy an open cone induction kit for their car. however they are not good for the engine, as they tend to take in alot of hot air into the engine from inside the engine bay. The best air filters tend to be a performance panel filter (e.g. K +N panel filter) or a different form of enclosed air filter (e.g. BMC carbon fibre induction kit). Most people will say that the original BMW air filters are the best - and they are very good and normally better than the open cone filters.

Another upgrade is to buy a chip for the ECU. Installing a chip can induce the engine into producing up to 12 extra BHP. It is achieved by giving the car a different fuel pattern to run on (in simple terms) which increases the rev limiter, increase the low end torque and makes the car pull better over the full rev range.

A less common modification though is a supercharger conversion. Possibly the most famous supercharged 318iS on the E30 zone is Appletree's iS with Eaton m45 supercharger

Aluminium flywheels are becoming a more popular upgrade for the M42 engines. Replacing the dual mass flywheel with an aluminium version reduces the strain on the engine drastically. Instead of the stock 27 lbs the aluminium flywheel only weighs abouut 9lbs. The reduced weight means that the engine can acelerate alot faster because there is less load on the engine. However because there is less weight it does mean that between gear changes the revs drop very quickly so it is possible to stall the engine between changes. But owners who have got aluminium flywheels do say that you can get used to the drop in the revs and it soon doesn't become a problem by either quickly changing gear or bliping the throttle between gears to sustain revs. Unfortunately the standard duel mass flywheel has springs in the flywheel (and not the clutch) which reduce/stop chatter created. The aluminium flywheels do not have this so a quiet chatter can be heard and the idle can some times be lumpy. Not all M42's came with dual mass fly wheels which is a common misconception. A cheaper and more road freindly alternative to an aluminium flywheel is to fit an M20 flywheel and clutch assembley.

Most recently COP conversions have become popular. COP stands for Coil On Plug and locates a set of M50 coil packs onto the spark plugs as opposed to having the standard packs on the wing and HT leads.

Useful websites

BP's E30 318iS website

The M42 club

**Part numbers were correct at time of typing, some may have been superceeded my a newer part. You use this information at your own risk - contact your local dealer to double check quantities/part numbers**