M42
The BMW M42 is a 4-cylinder 16-valve engine, fitted to the 318iS as well as early E36 models.
Contents
History
In E30 form it's twin cam 16v 4cyl 1796cc engine. It is an aluminium alloy engine which shares a development history with the M1, M5 and M635CSi engines.
The M42 is the last chain-driven engine fitted to the E30, and the first 16-valve unit. It featured a number of innovations that made it a far more modern engine than any other fitted to the E30, including a twin-valve throttle body, coil pack ignition and bi-concave combustion chambers. This made the 318iS both an economical and performance model, with good power and torque characteristics.
The engine also saw service in the E36, which added a serpentine belt front pulley system and a different intake manifold. It was finally superseded in that model by the M44.
The engine produces 136BHP at 6000RPM and 127 ft lbs of torque at 4600RPM
Versions
| Engine | Displacement | Power | Torque | Redline | Year |
|---|---|---|---|---|---|
| M42B18 | 1.8 L (1796 cc/110 in³) | 101 kW (136 hp) @ 6000 | 175 N·m (129 ft·lbf) @ 4500 | 6300 | 1989-96 |
| 100 kW (134 hp) @ 5500 | 172 N·m (127 ft·lbf) @ 4500 | 6300 | 1989-96 |
Components
The engine in all E30s is a three-part design, featuring a main Block with a Sump at the bottom and a Head at the top.
Sump
The M42 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 using twenty 10mm nuts.
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.
Oil Pump
Sump Gasket
The sump gasket seals the upper sump to the block. Its design features an internal portion that seals off the oil pickup pipe to the oil pump from the rest of the sump. Unfortunately, due to the problem of sump bolts, it is possible for the gasket to slip and allow the oil pump to suck in air instead of oil; potentially causing oil starvation and engine damage.
Block
The iron block is bored to 84mm. The cylinders have a maximum ovality of: 0.01mm/0.0004" with an identical maximum taper. Compression pressures : 10-11bar (143-156psi):
Crankshaft
Crankshaft : End play: 0.0031-0.0064"
Piston Rods
Con-rods : Max. weight variance without bearing shells: 4g/14oz split equally between big and small ends
Pistons
Pistons : Clearance: 0.0004-0.0016"
Piston rings : Gap: Top & bottom compression rings = 0.0080-0.0160" ; oil ring = 0.0080-0.0180"
Firing order: 1-3-4-2
Head
The engine has hydraulic tappets which reduce the maintenance of the engine.
Cylinder head : Height = 140mm/5.512"; minimum height = 139.55mm/5.494"
Rocker Cover
The top of the rocker cover has a vapour/liquid separator which reduces oil consumption of the engine and bi-concave combustion chambers.
When removing and replacing the rocker cover, it is worth replacing the rocker cover gasket.
Cams
Being a 16V engine, the M42 head features two camshafts; an Intake and an Exhaust.
Camshaft : Duration: inlet 252 exhaust 252 Lift: inlet 10.2 exhaust 10.2
Lobe height: 1.8755-1.8803"
Valves
Valves : Seat angle: 45 degrees
Valve stem to guide clearance: 0.020"
Inlet: Solid, stem diameter 6.975mm/0.2756", head diameter 33mm/1.299"
Exhaust: Sodium filled, diameter 6.975mm/0.2756", head diameter 30.5mm/1.201"
Seat diameter: inlet = 31.6mm/1.244", exhaust = 29.1mm/1.146"
Seat width: 1.4-1.9mm/0.055-0.075"
Valve clearance : None, automatically compensated by hydraulic tappets
Rocker Arms
Head Gasket
Timing Chain
Breather Hose
To balance the pressure inside the head, a rubber hose runs from the top of the rocker cover to the throttle body.
Intake Manifold
The inlet manifold is a two pieces design aimed at improving the low down torque of the engine.
Throttle Body
Unlike other throttle bodies on E30 engines, the M42 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.
Ancilliaries
Flywheel
Starter Motor
Engine Mounts
Torques
When working on any engine, it is important to tighten up all bolts only to their required tightness and no further. Use the following table as a guide:
| Nm | ft-lbs | |
|---|---|---|
| Big ends - Step 1 | 23 | 17 |
| Big ends - Step 2 | +70 degrees | |
| Camshaft sprocket | 13-17 | 10-12 |
| Camshaft bearing cap bolts | 13-17 | 10-12 |
| Crankshaft damper | 300-320 | 217-231 |
| Cylinder head Step 1 | 30-35 | 22-25 |
| Cylinder head Step 2 | +90-95 degrees | |
| Cylinder head Step 3 | +90-95 degrees | |
| Exhaust manifold | 22-24 | 17-18 |
| Flywheel | 82-94 | |
| Intake manifold | 13-17 | 10-12 |
| Main bearings Step 1 | 20-25 | 14-18 |
| Main bearings Step 2 | +47-53 degree turn | |
| Viscous fan coupling (LH threads) | 40-50 | 29-36 |
| Timing chain tensioner: | 23-27 | 17-19 |
Servicing
Main article: Basic M42 Servicing
Every engine needs its fluids and filters changed regularly. And while the M42 is chain-driven, it helps to replace the chain tensioner occasionally to prevent the chain slipping and killing the engine. Learn more about changing the chain tensioner.
Adjusting Timing Chain
Main article: Adjusting M42 Cam Timing
Common Problems
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 warranty.
| Part | Qty | Part Number | Part | Qty | Part Number | |
|---|---|---|---|---|---|---|
| Gasket | 1 | 111 217 215 46 | Gasket | 1 | 116 117 344 90 | |
| Bolt set | 1 | 111 217 219 39 | Nut | 4 | 183 017 377 74 | |
| Valve cover | 1 | 111 217 218 76 | Valve cover | 3 | 111 217 214 75 | |
| Gasket | 1 | 111 412 478 49 | Gasket | 1 | 115 317 211 72 | |
| Gasket | 1 | 111 412 478 37 | Gasket | 1 | 116 117 346 84 | |
| O-ring | 1 | 121 417 272 20 | O-ring | 1 | 115 317 212 18 | |
| Seal ring | 1 | 071 199 633 55 | Throttle-b | 2 | 135 412 474 00 | |
| Gasket | 1 | 183 017 119 69 | Gasket set | 1 | 111 417 219 19 | |
| Antifreeze | 1 | 821 414 677 04 |
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 relatively easy to change the chain tensioner. However, you can also re-fit an M44 tensioner. It is recommended that you change the tensioner as soon as possible when the symptoms 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.
Loose Sump Bolts
Due to the two-part design of M42 and M40 sumps, there is a common issue of internal sump bolts working loose. Not only can this cause oil leaks, but there's the threat of oil starvation to critical parts as the sump gaskets themselves work loose and block essential oil channels. To prevent premature engine death, learn more about M42 sump bolts.
Common Upgrades
Coil On Plug
Coil On Plug (COP) locates a set of M50 coil packs onto the spark plugs as opposed to having the standard packs on the wing and HT leads. Learn more about installing coil on plug.
Throttle Body Heater Delete
Some users have found that removing the throttle body heater does make a noticeable impact on the engine, based on cooler air flowing through the intake. Learn more about removing your M42 throttle body heater.
M20 Flywheel
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 assembly.
Chips
A variety of performance Chips are available to perk up the performance of otherwise-standard M42s.
Stroker Engines
The M42 block is capable of much larger capacities and power than BMW made use of. If you'd like to rebuild your M42 engine into a larger capacity, learn more about the most common stroker permutations.
