BMW M20 engines
Engines

BMW M20 engines

17.02.2023 /

The BMW M20 engine series is an in-line six-cylinder single-camshaft petrol powertrain. The first production of the series began in 1977 and the last model rolled off the assembly line in 1993. The first models on which engines of this series were used were E12 520/6 and E21 320/6. Their minimum working volume is 2.0 liters, while the largest and latest version had 2.7 liters. Subsequently, the M20 became the basis for the creation of the M21 diesel engine.BMW M20 engines

Since the 1970s, due to increased consumer demand, BMW has required new engines for the 3 and 5 model series, which would be smaller than the already existing M30 series, however, while maintaining the six-cylinder inline configuration. The result was the 2-litre M20, which is still the smallest inline-six from BMW. With volumes from 1991 cubic meters. see up to 2693 cu. see these motors were used on models E12, E28, E34 5 series, E21 and E30 3 series.

Distinctive features of the M20 from the M30 are:

  • Timing belt instead of chain;
  • Cylinder diameter 91 mm instead of 100 mm;
  • The angle of inclination is 20 degrees instead of 30, like the M30.

Also, the M20 has a steel cylinder block, an aluminum block head, one camshaft with two valves per cylinder.

M20B20

This is the very first model of this series and it was used on two cars: E12 520/6 and E21 320/6. The cylinder diameter is 80 mm and the piston stroke is 66 mm. Initially, a Solex 4A1 carburetor with four chambers was used to form the mixture and feed it into the cylinder. With this system, a compression ratio of 9.2:1 was achieved and the top speed was 6400 rpm. The first 320 machines used electric fans for cooling, but from 1979 they began to use a fan with a thermal coupling.BMW M20 engines

In 1981, the M20V20 was injected with injection, having received the Bosh K-Jetronic system. Since 1981, rounded teeth have also been used on the camshaft belt to eliminate howling when the engine is running. The compression of the injection engine increased to 9.9:1, the value of the maximum speed of rotation decreased to 6200 rpm with the LE-Jetronic system. For the E30 model, the engine has undergone an upgrade in terms of replacing the cylinder head, a lighter block and new manifolds adapted to the LE-Jetronic system (M20B20LE). In 1987, for the second and last time, a new fuel supply and injection equipment, Bosh Motronic, was installed on the M20V20, with which the compression is 8.8: 1.

Engine operation M20V20

Motor power ranges from 121 to 127 hp. at speeds from 5800 to 6000 rpm, the torque varies from 160 to 174 N * m.

used on models

The M20B20kat is an improved version of the M20B20 created for the BMW 5 Series and features a number of features. The first thing that is fundamentally different is the presence of the Bosh Motronic system and a catalytic converter that was new at that time, which reduces the toxicity of emissions produced by the engine.

M20B23

Six months after the start of production of the first M20V20 in 1977, the production of injection (ported injection) M20V23 began. For its production, the same block head was used as for the carburetor M20V20, but with a crank extended to 76.8 mm. The cylinder diameter is still 80 mm. The distributed injection system, which was originally installed on this engine, is K-Jetronic. Subsequently, it was replaced by the then newer L-Jetronic and LE-Jetronic systems. The working volume of the engine is 2.3 liters, which is slightly more than the previous one, however, the increase in power is already noticeable: 137-147 hp. at 5300 rpm. M20B23 and M20B20 are the last representatives of the series, produced before 1987 with the Jetronic system.BMW M20 engines

used on models

M20B25

This motor replaced the previous two, produced only with the Bosh Motronic injection system of various versions. Displacement 2494 cu. cm allows you to develop 174 hp. (without converter) at 6500 rpm, which significantly exceeded the performance of the smaller representatives of the series. The cylinder diameter has grown to 84 mm, and the piston stroke to 75 mm. Compression remained at the same level - 9.7:1. Also on updated versions, Motronic 1.3 systems appeared, which reduced engine performance. In addition, the catalytic converter reduced power to 169 hp, however, it was not installed on all cars.

used on models

The M20V27 is BMW's largest and most powerful M20 engine. It was designed to be more efficient and torquey at lower revs, which was not the usual thing for BMW inline-sixes running at a maximum of 6000 rpm. Unlike the M20B25, the piston stroke has grown to 81 mm, and the cylinder diameter to 84 mm. The block head is somewhat different from the B25, the camshaft is also different, but the valves remain the same.

Valve springs are softer, absorbing more excess energy, which increased efficiency. Also for this engine, a new intake manifold with elongated channels is used, and the throttle is the same as in the rest of the M20. Thanks to these changes, the upper limit of engine speed has been reduced to 4800 rpm. The compression in these engines depended on the market to which they were delivered: cars with a compression of 11:1 were driving in the USA, and 9.0:1 were sold in Europe.

used on models

The power produced by this model does not exceed the rest - 121-127 hp, but the torque with a margin of 14 N * m from the highest (M20B25) is 240 N * m at 3250 rpm.

Service

For this series of engines, approximately the same requirements for operation and oils used. It is better to use SAE semi-synthetics with a viscosity of 10w-40, 5w-40, 0w-40. In some cases, it is recommended to fill synthetics for one replacement cycle. Oil manufacturers worth paying attention to: Liqui Molly, Care, check every 10 km, replacement of consumables - it's like everyone else. But it is worth remembering one feature of the BMW as a whole - you need to carefully monitor the level of fluids, since gaskets often become unusable and begin to leak. However, this is not such a serious drawback, since it is solved by purchasing components from good materials.

Regarding the location of the engine number - since the block is of the same design - the number for all models of the series is located above the spark plugs, in the upper part of the block.

M20 engines and their characteristics

EngineHP/rpmN*m/r/minYears of production
M20B20120/6000160/40001976-1982
125/5800170/40001981-1982
122/5800170/40001982-1984
125/6000174/40001984-1987
125/6000190/45001986-1992
M20B23140/5300190/45001977-1982
135/5300205/40001982-1984
146/6000205/40001984-1987
M20B25172/5800226/40001985-1987
167/5800222/43001987-1991
M20B27121/4250240/32501982-1987
125/4250240/32501987-1992

 Tuning and swap

The topic of tuning for BMW is well disclosed, but first of all it is worth understanding whether a particular car needs it or not. The simplest thing that is usually done with the M20 series is the installation of a turbine and chip tuning, removing the catalyst, if any. These upgrades allow you to get up to 200 hp. from such a new and small motor - an almost European variation on the theme of small powerful engines, which has been practiced and practiced in Japan to this day.

Often, owners of cars from such old years of production think about replacing the engine, since the resource for 20 or more years is impressive. Modern engines of the new BMW and Toyota come to the rescue here, primarily attracting by their prevalence and reliability. Also, the power characteristics of many modern engines up to 3 liters will allow them to be used without replacing the gearbox. In the case of installing an internal combustion engine that greatly exceeds the original characteristics, the checkpoint will also have to be set accordingly.

Also, if you own a very old BMW from the M20 before 1986, you can upgrade its system to a more modern one and get better dynamics. Some install systems based on specific operating conditions, or want to achieve better traction “on the bottoms”.

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