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  • BMW M20 Engine (1977-1993)
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History

BMW M20 Engine

1977 to 1993

 BMW M20 Engine specs

 

The BMW M20 is a straight-six SOHC piston engine produced from 1977-1993. It was released in 1977 in the E12 520/6 and E21 320/6 and began to be phased out following the introduction of the M50 engine in 1990.

Like the larger capacity M30 engine from which it is derived, the M20 has a SOHC and 2 valves per cylinder. While the M30 camshaft is chain driven, the M20 camshaft and auxiliary shaft are driven by a timing belt. Initially released with a carburetor, later models used Bosch fuel injection.

History

The BMW M20 was developed in the mid-1970s as a "small" six-cylinder, since the 1968 built "big" six-cylinder BMW M30 was not suitable for the BMW E21 due to its dimensions . The cylinder spacing of the M30 was 100 mm, for the M20 a cylinder spacing of 91 mm was chosen, which resulted in a reduction of the outer dimensions. The basic features were designed by Alexander von Falkenhausen , the engine was ready for series production under Dr.-Ing. Karlheinz Lange. Originally conceived as a 2.3-liter engine, followed in the German market a 2-liter version, in the North American market there was in 1981 a 2.7-liter version, the eta version. Since the performance of the eta engine fell short of customer expectations, BMW was the last of the M20 family to develop a more powerful 2.5-liter engine. The eta engine was also available on the German market from the 1983rd  specifically for the Austrian market the 2-liter M20 was offered throttled with 88 kW. 

The BMW M20 was produced starting in 1976 by BMW engine construction in Munich and in parallel from 1982  in the BMW engine plant Steyr . By April 1990, 1.7 million cylinder heads were manufactured for the engine in Munich, whereby the production of the M20 engines in Munich was discontinued in favor of the successor BMW M50 . At the Steyr plant, the M20 was still being built in small numbers. On 27 November 1992 in Steyr ran out of the cylinder head line M20, the last M21 cylinder heads had been made already on 14 February 1,992th  The last motor, the motor assembly M20 / 21 was on 17 December 1992 in Steyr from the tape. At that time, the BMW M20 had already been largely replaced by the built since 1990 and four-valve technology much more modern six-cylinder engine BMW M50.

With displacements ranging from 1991 cc to 2693 cc, it was the "little brother" to the larger BMW M30. It has 91 mm (3.6 in) bore-spacing instead of the 100 mm (3.9 in) of the M30 six-cylinder and the M10 four-cylinder engines.Powering the E21 and E30 3-Series, as well as E12, E28 and E34 5 Series cars, it was produced for nearly two decades, with the last examples powering the E30 325i touring built until April 1993.Early versions of the M20 were sometimes referred to as the "M60", although the M60 code has since been used by BMW for a V8 engine produced from 1992-1996. The M20 was the basis for the M21 diesel engine, and the loosely related M70 V12.

The M20 is a stationary and slightly inclined in-line six-cylinder engine with OHC valve control that is water-cooled and operates after the Ottover process . It has a slightly short-stroke design, the bore is 80 mm, the stroke is 76.8 mm  or 66 mm.  Later, it was also 84 mm bore, 75 mm and 81 mm stroke. Thus, the four displacement variants 2.0 l, 2.3 l, 2.5 l and 2.7 l with an output of 88 kW yield (120 hp) to 126 kW (171 hp).

The engine block is made of gray cast iron.  For all engines, the cylinder spacing is 91 mm. First, a cast crankshaft was used. 

The cylinder head made of aluminum is one-piece and designed as a cross-flow cylinder head .For the first time in the BMW was overhead camshaft by means of toothed belt instead of the timing chain driven. The camshaft actuates 2 V-shaped valvesper cylinder via rocker arms .

Depending on the construction time, size and series, a double register carburetor Solex 4A1 (320/6 or 520/6) and later a mechanical ( K-Jetronic ) or electronic ( L-Jetronic / Motronic ) intake manifold injection were used for mixture preparation of the unit Models 320i / 323i / 325i / 520i / 525i. Alpina , Schnitzer and Hartge offered the engine performance-boosted with up to 154.5 kW (210 hp), with the built-in Alpina C2 and B3 M20 versions have 2.7 liter displacement. The hallmark of the BMW M20 with intake manifold injection is the cast intake bridge and the vibrating tube charging system realized with itin which the natural vibration of the air column in a narrow speed range acts as a slight charge. This intake manifold differs only minimally in the respective displacement variants. Greater, though not immediately apparent, changes were experienced in the eta versions (2.7 l).

 
Configuration Straight-six engine
Displacement
  • 2.0 L (1991 cc; 121.5 cu in)
  • 2.3 L (2316 cc; 141.3 cu in)
  • 2.5 L (2494 cc; 152.2 cu in)
  • 2.7 L (2693 cc; 164.3 cu in)
Cylinder bore
  • 80 mm (3.1 in) (2.0, 2.3)
  • 84 mm (3.3 in) (2.5, 2.7)
Piston stroke
  • 66 mm (2.6 in) (2.0)
  • 75 mm (3.0 in) (2.5)
  • 76.8 mm (3.0 in) (2.3)
  • 81 mm (3.2 in) (2.7)

 

M20B20

BMW M20 M20B25 Engine

The first models to use the M20 were the E12 520/6 and the E21 320/6, which used the 1991 cc M20B20. This engine uses a bore of 80 mm (3.1 in) and a stroke of 66 mm (2.6 in). Fuel was supplied by a Solex 4A1 four-barrel carburetor.

The M20B20 first became fuel-injected in the 1982 520i, with Bosch K-Jetronic used. In 1984, the fuel injection was updated to L-Jetronic. In 1987, the M20B20 was again revised with the addition of Bosch Motronic engine management and a catalytic converter.

Applications:

  • 1977–1981 E12 520/6
  • 1979–1983 E21 320/6
  • 1982–1984 E28 520
  • 1982–1988 E28 520i
  • 1983–1992 E30 320i
  • 1988–1990 E34 520i

M20B23

The 2.3 litre M20B23 used the same head (known as "731") and block as the carbureted 2.0 litre but used a longer 76.8 mm (3.0 in) stroke crank. The engine was first used in E21 323i and was replaced by the M20B25 in 1985.

The E30 version used L-Jetronic. and initially produced 102 kW (137 hp), which was increased to 110 kW (150 hp) in 1984. The 102 kW version continued to be available in certain markets with strict emissions regulations, such as Switzerland, until replaced by the 325i.

The M20B23 was not sold in North America.

Applications:

  • 1977–1982 E21 323i
  • 1982–1985 E30 323i

M20B25

BMW M20 M20B25 Engine block

The M20B25 has a capacity of 2494 cc and produced 126 kW (169 hp) (without a catalytic converter). The M20B25 head is known as "885" (since the casting number ends in 885), it has a bore of 84 mm (3.3 in), a stroke of 75 mm (3.0 in), a compression ratio of 9,7:1 and used the Bosch Motronic 1.1/1.3 engine management system. North American models used a lower compression ratio of 8.8:1.

Applications:

  • 1986–1993 E30 325i, 325iS, 325iC, 325iX
  • 1989–1990 E34 525i
  • 1988–1991 Z1

BMW M20 M20B25 Engine sump crank

M20B27

The 2693 cc M20B27 was designed for efficiency (thus the e for the Greek letter eta in 325e) and low-rev torque. Compared with the M20B25, the stroke is increased from 75 mm (3.0 in) to 81 mm (3.2 in). The B27 used the head casting of '200' which had smaller valves, different camshafts, fewer cam journals, and single valve springs to increase efficiency. Due to these changes the rev limit on the B27 was reduced.

The eta engine has longer intake manifolds, changed timing and reduced coefficient of friction compared to the conventional M20 engine through measures such as softer valve springs, reduced piston ring preload and only four camshaft bearings. Due to the large displacement of 2.7 liters, the eta version has a much higher torque at low speeds. The maximum value of 178 Nm of the 2.0-liter engine reached the 2.7-liter engine already below 1000 / min, the maximum value is at 240 Nm at 3250 / min and thus approximately at the level of the time in the 528i or 728i offered "large" M30 six-cylinder with 2.8 liter displacement, which, however, a significantly higher performance (135 kW / 184 hp at 5400 / min) achieved. The eta engine achieves an exceptionally smooth engine run, good starting characteristics and low fuel consumption thanks to its technologically advanced Motronic control unit, which was designed for the 1980s. However, since it does not correspond to the typical BMW character of high-speed engines, the market success of the eta models was limited it emerged 305,982 pieces. 1986, the eta engine was revised. By a modified cylinder head (M20B25 from) the rated power was increased to 95 kW, the final speed was at 5300 min . 

Power output is 121 hp (90 kW) at 4,250 rpm for M20B27 engines produced up until 1986 and 127 hp (95 kW) at 4,800 rpm for the "325es" model produced in 1987. Peak torque is 170 lb·ft (230 N·m) at 3,250 rpm for M20B27 engines. In 1987, the fuel injection was upgraded from Motronic 1.0 to Motronic 1.1/1.3.In the early 1990's BMW South Africa used components from the Alpina C3 2.7 to produce a E30 specifically for Stannic Group N production car racing. The first iteration of this engine used in the E30 325iS produced 145kw and the second revision, often referred to as "Evo2" or on the VIN plate as "HP2" produced 155kw.

Applications:

  • 1982–1987 E30 325e, 325es
  • 1982–1988 E28 525e (called 528e in North America)
  • 1989–1992 E30 325iS (Only available in South Africa)

Technical

  • BMW M20 Engine Technical details and specifications (1977-1993)

    BMW 3 Series (E30) 2.3L 323i


    No. of cylinders 6/OHC
    Capacity 2316cc
    Firing order 1-5-3-6-2-4
    Compression ratio 9.8:1
    Suitable for unleaded petrol Yes
    Fuel system Make Bosch LE-Jetronic
    Ignition coil Make Bosch Type 0 221 122 319
    Distributor Make Bosch No. 0 237 304 025/033
    Distributor Contact breaker gap 0.35-0.70mm
    Thermostat opens 80°C
    Starter motor Make Bosch Type 0 001 311 125
    Minimum starting voltage 10.0V
    Maximum cranking amps 135-165a
    Alternator Make Bosch Type 0 120 469 617
    Regulated voltage 13.5-14.2V

    © Motor car History

     

    BMW M20 Engine Technical data  (1977-1993) 

     
    engine capacity Bore × stroke compression Power at 1 / min Torque at 1 / min construction time
    M20B20VE 1990 cm3 80.0 mm × 66.0 mm 9.2: 1 90 kW (122 hp) at 6000 163 Nm (16.5 kpm) at 4000 1977-1982
    M20B20 9.8: 1 92 kW (125 hp) at 5800 170 Nm (17.3 kpm) at 4000 1983-1985
    9.8: 1 95 kW (129 hp) at 6000 174 Nm (17.7 kpm) at 4000 1985-1990
    M20B20 Cat 8.8: 1 95 kW (129 hp) at 6000 164 Nm (16.7 kpm) at 4300 1986-1992
    M20B23 2316 cm3 80.0 mm × 76.8 mm 9.8: 1 102 kW (139 hp) at 5300 205 Nm (20.9 kpm) at 4000 1983-09 / 1983
    9.8: 1 110 kW (150 hp) at 6000 205 Nm (20.9 kpm) at 4000 09 / 1983-1985
    9.5: 1 105 kW (143 hp) at 6000 176 Nm (17.9 kpm) at 4500 1978-1982
    M20B25 2494 cm3 84.0 mm × 75.0 mm 9.7: 1 126 kW (171 hp) at 5800 226 Nm (23.0 kpm) at 4000 1985-1986
    M20B25 Cat 8.8: 1 125 kW (170 hp) at 5800 222 Nm (22.6 kpm) at 4300 rpm 1986-1991
    M20B27 2693 cm3 84.0 mm × 81.0 mm 11.0: 1 92 kW (125 hp) at 4250 240 Nm (24.5 kpm) at 3250 1984-1985
    9.0: 1 90 kW (122 hp) at 4250 230 Nm (23.5 kpm) at 3250 1985-1987
    8.5: 1 95 kW (129 hp) at 4800 230 Nm (23.5 kpm) at 3200 1987-1988

    The mass of the engines was between 170 and 175 kg between that of the four-cylinder engine of the type M10 and that of the large six-cylinder engines of the type BMW M30. 

    Usage overview 

    Engine code (old scheme) engine code start of production end of production Performance (DIN-PS) Power kW) mixture preparation use
    M60 / 2 M20B20VE 09/1977 1982 122 hp 90 kW Double register 
    carburettor Solex 4A1
    E21320 
    E12520
    M60 M20B20KE 09/1981 07/1985 125 hp 92 kW K-Jetronic E30320i 
    E28520i
    M60 M20B20LE 09/1982 07/1985 125 hp 92 kW LE-Jetronic E30 320i 
    E28 520i
      M20B20LE 09/1982 07/1985 125 hp 92 kW L-Jetronic E30 320i 
    E28 520i
      M20B20LE ? ? 120 hp 88 kW L-Jetronic E28 520i
      M20B20Kat 09/1986 1991 129 hp 95 kW Bosch Motronic DME1.1 E30 320i 
    E28 520i 
    E34520i
    M60 / 5 M20B23LE 1983 1985 139 hp 102 kW Bosch L-Jetronic E30 323i
    M60 / 5 M20B23KE 02/1978 1982 143 hp 105 kW K-Jetronic E21 323i
      M20B23LE 1983 1985 150 hp 110 kW Bosch L-Jetronic E30 323i
      M20B25 1985 1986 171 hp 126 kW Bosch MEMotronic E30 325i / iX
      M20B25Kat 1986 1992 170 hp 125 kW Bosch DME 1.3 E30 325i / iX 
    Z1
    E34 525i
      M20B27ME 1983 1984 125 hp 92 kW Bosch DME ML1 E28525e
      M20B27Kat 1984 1986 122 hp 90 kW Bosch DME ML E30 325e
    E28 525e
      M20B27Kat 1986 1988 129 hp 95 kW Bosch DME1.1 E30 325e
    E28 525e
      M20B27Kat ? ? 120 hp 88 kW Bosch DME E28 525e

     

    Models
    Engine Displacement Power Torque Redline Comp Years Cars Market/Cat Fuel feed
    M20B20 2.0 L (1,990 cc/121 in³) 90 kW (122 PS; 121 hp) at 6,000 16.3 kg·m (160 N·m; 118 lb·ft) at 4,000 6,400 9.2:1 1977.09-1981 320, 520 EU - 1x4-bbl Solex
    92 kW (125 PS; 123 hp) at 5,800 17.3 kg·m (170 N·m; 125 lb·ft) at 4,000 6,400 9.8:1 1982-1985 320i EU - L-Jetronic
    92.5 kW (126 PS; 124 hp) at 5,800 17.3 kg·m (170 N·m; 125 lb·ft) at 4,000   9.9:1 1981.06-1985 520i EU - K-Jetronic
    95 kW (129 PS; 127 hp) at 6,000 17.7 kg·m (174 N·m; 128 lb·ft) at 4,000 6,200 9.8:1 1985-1990 320i, 520i EU - LE-Jetronic
    95 kW (129 PS; 127 hp) at 6,000 16.7 kg·m (164 N·m; 121 lb·ft) at 4,300 6,200 8.8:1 1986-1992 320i, 520i EU X ME-Motronic
    M20B23 2.3 L (2,316 cc/141 in³) 105 kW (143 PS; 141 hp) at 5,300 19.4 kg·m (190 N·m; 140 lb·ft) at 4,500 6,400 9.5:1 1978-1982 323i EU - K-Jetronic
    102 kW (139 PS; 137 hp) at 5,300 20.9 kg·m (205 N·m; 151 lb·ft) at 4,000   9.8:1 1982.11-1985 323i EU - L-Jetronic
    110 kW (150 PS; 148 hp) at 6,000 20.9 kg·m (205 N·m; 151 lb·ft) at 4,000 6,500 9.8:1 1983.09-1985 323i EU - L-Jetronic
    M20B25 2.5 L (2,494 cc/152 in³) 126 kW (171 PS; 169 hp) at 5,800 23.0 kg·m (226 N·m; 166 lb·ft) at 4,000 6,500 9.7:1 1985.06-1990 325i EU - ME-Motronic
    125 kW (170 PS; 168 hp) at 5,800 22.6 kg·m (222 N·m; 163 lb·ft) at 4,300 6,500 8.8:1 1986-1993 325i EU, US X ME-Motronic
    M20B27 2.7 L (2,693 cc/164 in³) 90.5 kW (123 PS; 121 hp) at 4,250 23.5 kg·m (230 N·m; 170 lb·ft) at 3,250 4,800 9.0:1 1982-1987 325/e/es, 528e US X

    L-Jetronic/

    Motronic

    92 kW (125 PS; 123 hp) at 4,250 24.5 kg·m (240 N·m; 177 lb·ft) at 3,250 5,000 11.0:1 1983-1984 525e EU - L-Jetronic /
    Motronic
    95 kW (129 PS; 127 hp) at 4,250 24.5 kg·m (240 N·m; 177 lb·ft) at 3,250   10.2:1 1984-1988 325e,525e EU - ME-Motronic
    90 kW (122 PS; 121 hp) at 4,250 23.5 kg·m (230 N·m; 170 lb·ft) at 3,250 4,800 9.0:1 1984-1988 325e, 525e EU X ME-Motronic
    95 kW (129 PS; 127 hp) at 4,800 23.5 kg·m (230 N·m; 170 lb·ft) at 3,200 5,200 8.5:1 1987.09-1988.09 325, 528e US X ME-Motronic

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Service

  •  BMW M20 Engine Service Guide (1977-1993)

    BMW 3 Series (E30) 2.3L 323i

    Spark plugs Original equipment Bosch Type W8DC
    Spark plugs Electrode gap 0.7-0.8mm
    Spark plugs Tighten 24-28 Nm
    Spark plugs Make Autolite Type 64
    Spark plugs Make Champion Type N9YCC
    Spark plugs Make NGK Type BP5ES
    Valve clearance -INLET 0.25mm check cold 
    Valve clearance -EXHAUST 0.25mm check cold
    Drive belt size - alternator 9.5x965mm
    Drive belt size - PAS/AC 9.5x810mm
    Engine oil grade - moderate climate 10W/40 SAE or 15W/50 SAE
    Engine oil change 4.5 litres
    Manual gearbox oil 80W SAE 1.5 litres
    Automatic transmission 2.0 litres
    Differential oil rear 90W SAE 0.9 litres
    Cooling system 10.5 litres

    © Motor car History

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