BMW M50B25

The BMW M50B25 is a 2.5 liters (2,494 cc, 152.2 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 M50B25 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), a coil-on-plug ignition system, a knock sensor, and a lightweight plastic intake manifold.

It has an 84.0 mm (3.31 in) cylinder bore and 75.0 mm (2.95 in) piston stroke. This engine has a compression ratio rating of 10.0:1 and a redline of 6,500 rpm. The M50B25 engine produced 192 PS (141 kW; 189 HP) at 6,000 rpm of maximum output power and 245 N·m (25 kg·m, 180.6 ft·lb) at 4,700 rpm of peak torque.

The breakdown of the engine code is as follows:

• M50 – Engine Family
• B – Gasoline
• 25 – 2.5 Liter Displacement

General information

Cylinder block

The BMW M50B25 engine has a cast-iron cylinder block, bore is 84.0 mm (3.31 in) and stroke is 75.0 mm (2.95 in). The compression ratio rating is 10.0:1. The pistons are each fitted with two compression rings and a single oil ring.

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 33.0 mm (1.30 in) in diameter and exhaust valves are 30.5 mm (1.20 in). Specifications of M50B25 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.

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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