BMW M50B25

BMW M50B25The 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

Engine Specifications
Engine codeM50B25
LayoutFour stroke, Inline-6 (Straight-6)
Fuel typeGasoline
Production1990-1992
Displacement2.5 L, 2,494 cc (152.2 cu in)
Fuel systemElectronic fuel injection (MS40.1)
Power adderNone
Max. horsepower192 PS (141 kW; 189 HP) at 6,000 rpm
Max. torque245 N·m (25 kg·m, 180.6 ft·lb) at 4,700 rpm
Firing order1-5-3-6-2-4
Dimensions (L x H x W):
Weight194 kg (428 lbs)

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.

Cylinder block
Cylinder block alloyCast-iron
Compression ratio:10.0:1
Cylinder bore:84.0 mm (3.31 in)
Piston stroke:75.0 mm (2.95 in)
Number of piston rings (compression / oil):2 / 1
Number of main bearings:7
Cylinder inner diameter (standard):84.000-84.014 mm (3.3071-3.3076 in)
Piston skirt diameter (standard):83.980 mm (3.3063 in)
Piston ring side clearance:Top0.020-0.052 mm (0.0008-0.002 in)
Second0.020-0.052 mm (0.0008-0.002 in)
Oil0.020-0.055 mm (0.0008-0.0022 in)
Piston ring end gap:Top0.200-0.400 mm (0.0079-0.0157 in)
Second0.200-0.400 mm (0.0079-0.0157 in)
Oil0.200-0.450 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 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.

Cylinder head
Valve Arrangement:DOHC, chain drive
Valves:24 (4 valves per cylinder)
Intake/Exhaust duration:240°/228°
Valve head diameter:INTAKE33.000 mm (1.2992 in)
EXHAUST30.500 mm (1.2008 in)
Valve steam diameter:INTAKE7.000 mm (0.2756 in)
EXHAUST7.000 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
Standard10.2 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 plugBosch: FGR7DQP, NGK: BKR6EQUP
Spark plug gap0.7 mm (0.028 in)

Vehicle applications

ModelYears Produced
BMW 525i, 525ix (E34)1990-1992
BMW 325i, 325is (E36)1991-1992
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