BMW M20B20

The 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

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.

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.

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

Vehicle applications

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