BMW M42 DOHC Straight-4 Engine

The BMW M42 is a straight-4 DOHC piston engine produced from 1989 to 1996. It was produced alongside the M40 straight-4 engine, as the higher performance engine. It was also used in North American versions of the E36 318i instead of the M40. The M42 was replaced by the M44, which was introduced in 1996.

Compared with the M40, the M42 features a DOHC valvetrain, a timing chain, hydraulic valve lifters and an increased 10:1 compression ratio. Later versions of the M42 also feature a dual length intake manifold (called "DISA").

The M42 was used as the basis for the S42 racing engine, which powered the BMW 320i in the German Super Tourenwagen Cup.

Design

Following BMW's typical construction techniques at the time, the motor incorporates a cast-iron block and aluminium head. Weight-saving measures include aluminium chain cases, oil sump, motor mount arms, accessory mounts and a cartridge-style oil filter housing. Closely related to the SOHC M40, the M42's DOHC 16 valve head and chain-driven cams provided increased power in comparison to the M40.

The M42 also incorporates other performance features such as a forged steel crankshaft and welded tubular stainless steel exhaust manifold instead of the more typical cast-iron items. BMW also fitted hydraulic motor mounts to decrease the inline four's inherent noise, vibration and harshness (NVH) compared to the smoother inline sixes already in production at that time.

When installed in the BMW E30, a two-piece oil pan with a removable front sump was fitted to the M42. In this two-piece arrangement, the upper oil pan casting incorporates the oil pump's supply passage, and is sealed to the crankcase oil filter housing with a paper gasket. This can cause problems, because thermal cycles and engine vibration tend to loosen the six 10mm upper pan mounting bolts inside the motor.

All versions featured a low-maintenance timing chain with a self-adjusting hydraulic chain tensioner and hydraulic valve tappets. The M42 also incorporates the Bosch Motronic M1.7 DME, eliminating a distributor in favor of fully electronic ignition timing.The DME was configured to fire four individual remotely mounted coils. Furthermore, in markets that required emissions controls, the DME also incorporates an upstream O2 sensor and three-way catalyst.

Running changes

The earliest versions of the M42 developed problems with the camshaft chain drive. The hydraulic tensioner,chain guides, idler wheel and rear lower chain case have all been updated to resolve mechanical wear problems experienced in the early versions of the M42. Since the updated cam chain tensioner is shared with the M44, people commonly refer to the revised tensioner as a "M44 tensioner".

In the final versions of the M42, BMW engineered a dual length intake manifold (called "DISA" by BMW)

Recalls

Early models of the M42 experienced failures of a profile gasket sealing the lower cam chain case to the underside of the cylinder head. This gasket seals the primary coolant passage within the timing chain case. A significant failure would thus discharge pressurized steam and hot coolant into the timing chain case. In many cases this coolant rapidly contaminates the motor oil in the sump, causing main bearing failure. BMW updated the profile gasket material and instituted a program to repair motors under warranty. In extreme cases, the aluminum mating surfaces in the head and chain case would corrode.

Models

M42B18

The M42B18 has a displacement of 1,796 cc, which is achieved through a bore of 84 mm and a stroke of 81 mm. The engine uses Bosch Motronic 1.7 fuel injection. Versions equipped with a catalytic converter produce 100 kW and 172 Nm. and meets with Euro2 norms.

Applications:

• 1989-1991 E30 318i (only North American models)
• 1989–1991 E30 318iS
• 1992–1996 E36 318i/318ti (only North American and South African models)
• 1992–1996 E36 318iS
• 1996 Z3

S42B20

A racing version of the M42 Engine, called the S42 was used in BMW's 320 4-door touring car, participating in the German racing series called STW (Super Tourenwagen Cup). It differed by having individual throttle bodies (ITB) for each cylinder and its capacity was enlarged to 1999 cc. It had eight fuel injectors instead of the standard four. Valve cover and airbox were entirely made of carbon fiber. Lubrication was provided by a dry sump system. Compression ratio was increased and a lightweight head installed.

Horsepower evolution steps of the S42 Engine:

In its final evolution, this engine develops 158 HP/l.