BMW M42
| BMW M42 | |
|---|---|
 |
|
| Overview | |
| Manufacturer | BMW |
| Production | 1989–1996 |
| Combustion chamber | |
| Configuration | DOHC Straight-4 |
| Displacement | 1,796 cc (110 cu in) |
| Chronology | |
| Predecessor | BMW M40 |
| Successor | BMW M44 |
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 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.
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.
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