The BMW M42 is a DOHC straight-four petrol engine which was produced from 1989-1996. It is BMW's first mass-production

DOHC An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion c ...

engine and was produced alongside the BMW M40 SOHC four-cylinder engine as the higher performance engine. The M42 was replaced by the BMW 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 10.0:1 compression ratio. Later versions of the M42 also feature a dual length intake manifold ("DISA"). The M42 was used as the basis for the S42 racing engine, which powered the BMW 320i in the German

Super Tourenwagen Cup The Super Tourenwagen Cup, or German Supertouring Championship, was a touring car racing series held between 1994 and 1999 in Germany. The championship was established when BMW and Audi both left the Deutsche Tourenwagen Meisterschaft (DTM) in 19 ...

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. Other features included a forged steel

crankshaft A crankshaft is a mechanical component used in a piston engine to convert the reciprocating motion into rotational motion. The crankshaft is a rotating shaft containing one or more crankpins, that are driven by the pistons via the connecting ...

and tubular stainless steel

exhaust manifold In automotive engineering, an exhaust manifold collects the exhaust gases from multiple cylinders into one pipe. The word ''manifold'' comes from the Old English word ''manigfeald'' (from the Anglo-Saxon ''manig'' anyand ''feald'' old and refe ...

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 Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. While noise and vibration can be readily measured, ...

compared to the smoother straight-six engines 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 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. From September 1993, the chain idler gear was replaced by a more reliable curved plastic guide, requiring a new design of front engine/chain casing. The M42 uses the Bosch Motronic M1.7 engine management system, eliminating a distributor in favor of fully electronic

ignition timing In a spark ignition internal combustion engine, ignition timing is the timing, relative to the current piston position and crankshaft angle, of the release of a spark in the combustion chamber near the end of the compression stroke. The need for ...

. The ignition system also uses a

coil-on-plug A distributor is an enclosed rotating switch used in spark-ignition internal combustion engines that have mechanically timed ignition. The distributor's main function is to route high voltage current from the ignition coil to the spark plugs ...

system. In markets that required emissions controls, the DME also incorporates an oxygen sensor and three-way

catalytic converter A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...

. From January 1995, the M42 (and all other BMW engines) received the EWS-II engine immobiliser with a revised ECU, a transponder chip in the ignition key, a plastic ring around the ignition lock (introduced with a new steering lock December 1994 in preparation) and an EWS transponder unit behind the glovebox. In the final versions of the M42, BMW engineered a dual length intake manifold (called "DISA" by BMW)

Versions

M42B18

The M42B18 has a

displacement Displacement may refer to: Physical sciences Mathematics and Physics * Displacement (geometry), is the difference between the final and initial position of a point trajectory (for instance, the center of mass of a moving object). The actual path ...

of , which is achieved through a bore of and a

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

of . Versions equipped with a catalytic converter produce and . and meet the Euro 2 emissions standard. Applications: * 1989–1991 E30 318is * 1990–1992 E30 318i (only North American models) * 1992–1995 E36 318i (only North American and South African models) * 1991–1995 E36 318is * 1994–1995 E36 318ti

S42B20

The racing version of the M42 engine is called the S42 and was used in BMW's 320 4-door touring car, participating in the German

. Compared with the M42, the S42 has individual throttle bodies, the displacement increased to , two fuel injectors per cylinder, an increased

compression ratio The compression ratio is the ratio between the volume of the cylinder and combustion chamber in an internal combustion engine at their maximum and minimum values. A fundamental specification for such engines, it is measured two ways: the stati ...

and a different cylinder head. The valve cover and airbox were made from carbon fiber and the lubrication system used a

dry sump A dry-sump system is a method to manage the lubricating motor oil in four-stroke and large two-stroke piston driven internal combustion engines. The dry-sump system uses two or more oil pumps and a separate oil reservoir, as opposed to a conve ...

. In 1994, the initial version of the S42B20 engine produced . Outputs gradually increased to for the final version in 1997.

Timing system revisions

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 were updated to resolve wear problems experienced in the early versions of the M42. The updated cam chain tensioner is shared with that of the later M44 engine. In September 1993, BMW redesigned the M42's timing chain guide rails, replacing the occasionally troublesome lower idler gear with a curved nylon guide rail. The idler gear's retaining bolt could break away from the timing case, often taking a chunk of alloy timing case with it.

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.

References

{{commons category, BMW M42 engine M42 Straight-four engines Gasoline engines by model