The BMW M50B20 is a 2.0 liters (1,990 cc, 121.4 cu·in) straight-six, four-stroke cycle natural aspirated gasoline engine from BMW M50-family. The engine was manufactured from 1990 to 1992.
The BMW M50B20 engine features a cast-iron block and aluminum head with a dual overhead camshaft (DOHC) and four valves per cylinder (24 in total). The engine is equipped with an electronic fuel injection system (DME M3.1), coil-on-plug ignition, a knock sensor, and a lightweight plastic intake manifold.
The engine has an 80.0 mm (3.15 in) cylinder bore and 66.0 mm (2.6 in) piston stroke. This engine has a compression ratio rating of 10.5:1 and a redline of 6,500 rpm. The BMW M50B20 engine produced 145 PS (110 kW; 147 HP) at 6,000 rpm of maximum output power and 190 N·m (19.4 kg·m, 140 ft·lb) at 4,700 rpm of peak torque.
The breakdown of the engine code is as follows:
- M50 – Engine Family
- B – Gasoline
- 20 – 2.0 Liter Displacement
General information
| Engine Specifications | |
| Engine code | M50B20 |
| Layout | Four stroke, Inline-6 (Straight-6) |
| Fuel type | Gasoline |
| Production | 1990-1992 |
| Displacement | 2.0 L, 1,990 cc (121.4 cu in) |
| Fuel system | Electronic fuel injection (DME3.1) |
| Power adder | None |
| Max. horsepower | 145 PS (110 kW; 147 HP) at 6,000 rpm |
| Max. torque | 190 N·m (19.4 kg·m, 140 ft·lb) at 4,700 rpm |
| Firing order | 1-5-3-6-2-4 |
| Dimensions (L x H x W): | – |
| Weight | 194 kg (428 lbs) |
Cylinder block
The BMW M50B20 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 pistons are each fitted with two compression rings and a single oil ring.
| Cylinder block | ||
| Cylinder block alloy | Cast iron | |
| Compression ratio: | 10.5:1 | |
| 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: | Top | 0.020-0.052 mm (0.0008-0.002 in) |
| Second | 0.020-0.052 mm (0.0008-0.002 in) | |
| Oil | 0.020-0.055 mm (0.0008-0.0022 in) | |
| Piston ring end gap: | Top | 0.200-0.400 mm (0.0079-0.0157 in) |
| Second | 0.200-0.400 mm (0.0079-0.0157 in) | |
| Oil | 0.200-0.450 mm (0.0079-0.0177 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:
- Step 1: 20 Nm; 2.04 kg·m; 14.76 ft·lb
- Step 2: Tighten bolts at the angle of 50°
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 dual overhead camshaft with four valves per cylinder. Intake valves are 30.0 mm (1.18 in) in diameter and exhaust valves are 27.0 mm (1.06 in). Specifications of M50B20 camshafts are as follows: duration is 240° for inlet and 228° for exhaust valves, valve lift is 9.7 and 8.8 mm, respectively. This motor is equipped with hydraulic lifters.
| Cylinder head | ||
| Valve Arrangement: | DOHC, chain drive | |
| Valves: | 24 (4 valves per cylinder) | |
| Intake/Exhaust duration: | 240°/228° | |
| Valve head diameter: | INTAKE | 30.000 mm (1.1811 in) |
| EXHAUST | 27.000 mm (1.063 in) | |
| Valve steam diameter: | INTAKE | 7.0 mm (0.2756 in) |
| EXHAUST | 7.0 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
| Compression pressure | |
| Standard | 10.2 kg/cm2 (9.9 bar, 145 psi) / 350 rpm |
| Oil system | |
| Recommended engine oil | 5W-30, 5W-40, 10W-30, 10W-40 |
| Oil type API | – |
| Engine oil capacity (Refill capacity) | With filter change: 5.75 L (6.08 US. qt, 5.06 Imp. qt.) |
| Oil change interval, km (miles) | 10,000 (6,000) |
| Ignition system | |
| Spark plug | Bosch: FGR7DQP, NGK: BKR6EQUP |
| Spark plug gap | 0.7 mm (0.028 in) |
Vehicle applications
| Model | Years Produced |
| BMW 520i (E34) | 1990-1992 |
| BMW 320i (E36) | 1991-1992 |
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