BMW M20B20

BMW M20B20The BMW M20B20 is a 2.0 liters (1,990 cc, 121.4 cu·in) straight-six, four-stroke cycle natural aspirated gasoline engine from BMW M20-family. The engine was manufactured from 1976 to 1992.

The BMW M20B20 engine features a cast-iron block and aluminum head with a single overhead camshaft (SOHC) and two valves per cylinder (12 in total). It has an 80.0 mm (3.15 in) cylinder bore and 66.0 mm (2.6 in) piston stroke.

An early version of this engine was equipped with the Solex 4A1 four-barrel carburetor. This engine has a compression ratio of 9.2:1 and a redline of 6,400 rpm. It produced 122 PS (90 kW; 121 HP) at 6,000 rpm of horsepower and 163 N·m (16.6 kg·m, 120.1 ft·lb) at 4,000 rpm of peak torque.

In 1981, the engine began to use a mechanical fuel injection system and the Bosch K-Jetronic engine management system. The compression ratio rating was increased to 9.9:1. In September 1982 the fuel system was updated to electronic fuel injection (LE-Jetronic) with a redline of 6,200 rpm.

In 1987, the M20B20 was revised with the addition of the Bosch Motronic engine management and catalytic converter. It has a compression ratio rating of 8.8:1. This engine produced 130 PS (95 kW; 127 HP) at 6,000 rpm of horsepower and 174 N·m (17.7 kg·m, 128.2 ft·lb) at 4,000 rpm of peak torque.

The breakdown of the engine code is as follows:

  • M20 – Engine Family
  • B – Gasoline
  • 20 – 2.0 Liter Displacement

General information

Engine Specifications
Engine codeM20B20
LayoutFour stroke, Inline-6 (Straight-6)
Fuel typeGasoline
Displacement2.0 L, 1,990 cc (121.4 cu in)
Fuel system Solex 4A1 four-barrel carburetor
Mechanical fuel injection system (Bosch K-Jetronic)
Electronic fuel injection system (Bosch LE-Jetronic, L-Jetronic, Motronic DME1.1/DME1.3)
Power adderNone
Max. horsepower From 122 PS (90 kW; 121 HP) at 6,000 rpm
to 129 PS (95 kW; 127 HP) at 6,000 rpm
Max. torque From 163 N·m (16.6 kg·m, 120.1 ft·lb) at 4,000 rpm
to 174 N·m (17.7 kg·m, 128.2 ft·lb) at 4,000 rpm
Firing order1-5-3-6-2-4
Dimensions (L x H x W):
Weight170 kg (374.8 lbs)

Cylinder block

The BMW M20B20 engine has a cast-iron cylinder block, bore is 80.0 mm (3.15 in) and stroke is 66.0 mm (2.6 in). The cylinder block, a monoblock specially cast structure. The pistons are each fitted with two compression rings and a single oil ring.

Cylinder block
Cylinder block alloyCast iron
Compression ratio:9.2:1, 9.9:1, 8.8:1
Cylinder bore:80.0 mm (3.15 in)
Piston stroke:66.0 mm (2.6 in)
Number of piston rings (compression / oil):2 / 1
Number of main bearings:7
Cylinder inner diameter (standard):80.000 mm (3.1496 in)
Piston skirt diameter (standard):79.980 mm (3.1488 in)
Piston ring side clearance:Top0.040-0.080 mm (0.0016-0.0031 in)
Second0.030-0.070 mm (0.0012-0.0028 in)
Oil0.020-0.050 mm (0.0008-0.002 in)
Piston ring end gap:Top0.200-0.500 mm (0.0079-0.0197 in)
Second0.200-0.500 mm (0.0079-0.0197 in)
Oil0.200-0.500 mm (0.0079-0.0197 in)
Crankshaft journal diameter:60.000 mm (2.3622 in)
Crankpin diameter:45.000 mm (1.7717 in)

Main bearing cap bolts tightening procedure and torque specs:

  • 60 Nm (6.12 kg·m; 44.28 ft·lb)

After securing bearing cap bolts, make sure crankshaft turns smoothly by hand.

Connecting rod bearing bolts

  • Step 1: 5 Nm; 0.51 kg·m; 3.69 ft·lb
  • Step 2: 20 Nm; 2.04 kg·m; 14.76 ft·lb
  • Step 3: Tighten bolts at the angle of 70°

Cylinder head

The cylinder head is made of an aluminum alloy with good cooling efficiency. The engine has a single overhead camshaft with two valves per cylinder. The camshaft is driven by a timing belt.

Intake valves are 40.0 mm (1.57 in) in diameter and exhaust valves are 34.0 mm (1.34 in). The valves are opened and closed by rocker arms. These rocker arms perform a dual function of cam follower valve adjuster, as one end contains the eccentric and the adjustment nut. The rocker arms pivot around rocker arm shafts.

Cylinder head
Valve Arrangement:SOHC, belt drive
Valves:12 (2 valves per cylinder)
Intake/Exhaust duration:
Valve head diameter:INTAKE40.0 mm (1.5748 in
EXHAUST34.0 mm (1.3386 in)
Valve steam diameter:INTAKE7.0 mm (0.2756 in)
EXHAUST7.0 mm (0.2756 in)

Head tightening procedure and torque specs:

  • Step 1: 30 Nm (3.06 kg·m; 22.14 ft·lb)
  • Step 2: Tighten bolts at the angle of 90°
  • Step 3: Once again, tighten bolts at the angle of 90°

Maintenance data

Valve clearance
Intake valve0.25 mm (0.010 in)
Exhaust valve0.25 mm (0.010 in)
Compression pressure
Minimum10.2 kg/cm2 (9.9 bar, 145 psi) / 350 rpm
Oil system
Recommended engine oil 5W-30, 5W-40, 10W-30, 10W-40, 10W-50, 15W-40, 15W-50
Oil type API
Engine oil capacity (Refill capacity) With filter change 4.25 l
Without filter change 4.0 l
Oil change interval, km (miles)10,000 (6,000)
Ignition system
Spark plugBosch: W8LCR, NGK: ZGR5A
Spark plug gap0.7 mm (0.028 in)

Vehicle applications

ModelYears Produced
BMW 520/6 (E12)1976–1981
BMW 320/6 (E21)1977–1982
BMW 520i (E28)1981–1982
BMW 520i (E28)1982–1984
BMW 320i (E30)1982–1984
BMW 520i (E28)1984–1987
BMW 320i (E30)1984–1987
BMW 520i (E28)1986–1987
BMW 320i (E30)1987–1992
BMW 520i (E34)1988–1990
Author: Sergei Wers
About: Co-founder and CEO of a multi-brand auto repair shop (engine repair, chassis repair, body repair and painting) for over 15 years. I have been developing internet sites with technical specifications for more than seven years.

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