The BMW M21 is a straight-six

diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to mechanical compression; thus, the diesel engine is a so-call ...

developed by the Bavarian engine manufacturer BMW. It has swirl chamber injection and is based on the M20

petrol engine A petrol engine (gasoline engine in American English) is an internal combustion engine designed to run on petrol (gasoline). Petrol engines can often be adapted to also run on fuels such as liquefied petroleum gas and ethanol blends (such as ''E ...

and was produced for BMW by the Upper Austrian

Steyr Steyr (; Central Bavarian: ''Steia'') is a statutory city, located in the Austrian federal state of Upper Austria. It is the administrative capital, though not part of Steyr-Land District. Steyr is Austria's 12th most populated town and the 3rd l ...

engine plant from 1983 to 1991. It was succeeded by the

M51 M51 or M-51 may refer to: * M-51 (Michigan highway), a state highway in Michigan * M51 highway (Russia) * M51 (Cape Town), a Metropolitan Route in Cape Town, South Africa * M51 Skysweeper, an anti-aircraft gun * M51 MACI mine * M51 SLBM, a Fre ...

Background

In the 1970s BMW decided to develop an engine, which would both be powerful and have a good fuel economy. This was caused by the oil crisis in 1973. In 1975 a group of BMW engineers started working on the M21 diesel engine, the M20 petrol engine was used as the basis. The Steyr engine plant was planned from the beginning to be the sole manufacturer of the new diesel engine. It started as a joint venture with Steyr-Daimler Puch in 1978, but in February 1982 BMW took over the reins. The first engines built there (in early 1982) were six-cylinder petrol units. Beginning in 1983, Ford was planning to buy 190,000 BMW turbodiesels over a period of several years. With the American diesel market imploding in the early 1980s, Ford only built a small number of Lincolns thus equipped and only for two model years. In 1983 at the IAA, the first passenger car was shown to the public which made use of the M21. It was the E28 524td, which has a top speed of and reaches in 12.9 s. This 5-series BMW was the fastest series production diesel car in the world in 1983. It has a fuel economy of .

Technical description

As per the M20, the M21 is water-cooled, has a cast iron block and a

SOHC 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 cha ...

valvetrain. The

camshaft A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...

is driven by a belt, each cylinder has one inlet and one outlet valve. Compared to the M20, the M21 has reinforced

connecting rod A connecting rod, also called a 'con rod', is the part of a piston engine which connects the piston to the crankshaft. Together with the crank, the connecting rod converts the reciprocating motion of the piston into the rotation of the cranksh ...

cylinder head In an internal combustion engine, the cylinder head (often abbreviated to simply "head") sits above the cylinders and forms the roof of the combustion chamber. In sidevalve engines, the head is a simple sheet of metal; whereas in more modern ov ...

s, pistons, valves and a reinforced

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 ...

with seven bearings. For faster engine startup the M21 has a glowplug system called ''instant start'', which reduces the time to reach starting temperature compared to similar diesel engines. The fuel is injected into swirl chambers. A Garrett

turbocharger In an internal combustion engine, a turbocharger (often called a turbo) is a forced induction device that is powered by the flow of exhaust gases. It uses this energy to compress the intake gas, forcing more air into the engine in order to pro ...

is used (without an

intercooler An intercooler is a heat exchanger used to cool a gas after compression. Often found in turbocharged engines, intercoolers are also used in air compressors, air conditioners, refrigeration and gas turbines. Internal combustion engines Mo ...

). Initially, the M21 was only available as a turbocharged engine. In 1985, BMW introduced a naturally aspirated version of the M21, which was popular in countries with a high motor vehicle tax. Initially, the fuel pump was controlled mechanically. From 1987, an electronically controlled fuel pump was used, which increased the torque output by . The updated engine has a smaller turbocharger, which improves response.

Models

Applications: * 1983 - 1988 E28 524td * 1985 - 1988 E28 524d (naturally aspirated) * 1985 - 1993 E30 324d (naturally aspirated) * 1985 - 1993 E30 324td * 1988 - 1991 E34 524td * 1984 - 1985 Continental Mark VII * 1984 - 1985

Lincoln Continental The Lincoln Continental is a series of mid-sized and full-sized luxury cars produced by Lincoln, a division of the American automaker Ford Motor Company. The model line was introduced following the construction of a personal vehicle for Edse ...

* 1986 - 1987 Vixen 21 TD and Vixen 21 XC * 1989 - 1991

Bertone Freeclimber The is an off-road vehicle built by Daihatsu between 1984 and 2002. The Rugger was also called the Rocky in most export markets, and Fourtrak in the United Kingdom. It has also received a series of different names elsewhere, which is why it is ...

* 1992

UMM Alter II The UMM Alter II is a Portuguese automobile produced by UMM from 1986–1994. UMM Alter II Phase I In 1986 the Alter II was released by the Portuguese automobile manufacturer União Metalo-Mecânica (UMM). It featured a new 4-speed manual ge ...

(four examples built)

References

Andreas in ''Bimmer''
Die BMW-Sportdiesel: Von 524td E28 über 530d E39 bis BMW M550d F10
published at 21 January 2012, retrieved at 9 April 2015. (german) Ronan Glon in ''RanWhenParked.net''
30 years ago: BMW introduces its first diesel engine
published at the 22nd of Juli 2013, retrieved at 9 April 2015.

Auto Motor und Sport ''Auto Motor und Sport'', often stylized as auto motor und sport and abbreviated AMS or AMuS, is a German automobile magazine. It is published fortnightly by Motor Presse Netzwerk's subsidiary Motor Presse Stuttgart, a specialist magazine publi ...

Der zweite 5er von BMW: Die Baureihe E28 Der unscheinbare Revoluzzer
retrieved at 9 April 2015. (german)
. Retrieved at 9 May 2016.
Retrieved at 3 January 2017. E30 Zone- M21
Retrieved at 3 January 2017. M21 Diesel engines by model Straight-six engines {{BMW automotive diesel engines: 1980s to 2000s

Background

Technical description

Models

See also

References