BMW M42

The BMW M42 is a straight-4 DOHC piston engine produced from 1989 to 1996. Following BMW's typical construction techniques, the motor incorporates a durable cast-iron block and aluminum head. Weight-saving measures include aluminum chain cases, oil sump, motor mount arms, accessory mounts and a cartridge-style oil filter housing. Closely related to the single cam M40, the DOHC 16 valve head and chain-driven cams provided a notable increase in power. It was used in North American versions of the E36 318i instead of the M40. The M42 also incorporated 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.

The M42 went through several minor revisions during production. All versions featured a low-maintenance timing chain with a self-adjusting hydraulic chain tensioner and hydraulic valve tappets. The M42 also incorporated 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 incorporated an upstream O2 sensor and three-way catalyst.