BMW M52B25TU

BMW M52B25 TUThe BMW M52B25TU is a 2.5 liters (2,494 cc, 152.20 cu-in) straight-six, four-stroke cycle natural aspirated gasoline engine from BMW M52-family. The engine was manufactured on Munich Plant (Munich, Germany) from 1998 to 2000. M52B25TU engine is a technical update (hence the designation TU) of the earlier M52B25 engine. The main “technical update” for M52TU was the addition of double VANOS.

The M52B25 TU engine features a cast-aluminum alloy cylinder block with cast-iron cylinder liners. The aluminum cylinder head uses chain-driven double overhead camshafts (DOHC) and four valves per cylinder (24 valves in total). It is equipped with a Siemens MS 42.0 DME (Digital Motor Electronics) system, double VANOS (Variable Valve Timing System from BMW) for both inlet and exhaust camshafts, Motor Driven Throttle Valve, dual length intake manifold (called “DISA” by BMW) and a distributorless ignition system with individual ignition coils for each cylinder.

This engine 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 of 10.5:1 and a redline of 6,500 rpm. It produced 170 PS (125 kW; 168 HP) at 5,500 rpm of maximum horsepower and 245 N·m (25 kg·m, 180.6 ft·lb) at 3,500 rpm of peak torque.

The breakdown of the engine code is as follows:

  • M52 – Engine Family
  • B – Gasoline
  • 25 – 2.5 Liter Displacement
  • TU – Technical update

General information

Engine Specifications
Engine codeM52TUB25
LayoutFour stroke, Inline-6 (Straight-6)
Fuel typeGasoline
Production1998-2000
Displacement2.5 L, 2,494 cc (152.19 cu in)
Fuel systemFuel injection system
Power adderNone
Max. horsepower170 PS (125 kW; 168 HP) at 5,500 rpm
Max. torque245 N·m (25 kg·m, 180.6 ft·lb) at 3,500 rpm
Firing order1-5-3-6-2-4
Dimensions (L x H x W):
Weight~175 kg(385 lbs)

Cylinder block

The M52B25TU cylinder block is cast aluminum alloy with cast iron cylinder liners, bore is 84.0 mm (3.31 in) and stroke is 75.0 mm (2.95 in). The cylinders are exposed on all sides to circulating coolant. The cast-iron counterweighted crankshaft rotates in replaceable split-shell main bearings. This engine used seven main bearings.

The forged steel connecting rods use replaceable split-shell bearings at the crankshaft end and solid bushings at the piston pin end. The pistons are of the three-ring type with two upper compression rings and a lower one-piece oil scraper ring. Full-floating piston pins are retained with circlips. The compression ratio rating is 10.5:1.

Cylinder block
Cylinder block alloyAluminum alloy
Compression ratio:10.5:1
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):84.000-84.010 mm (3.3071-3.3075 in)
Piston skirt diameter (standard):83.980-83.989 mm (3.3063-3.3066 in)
Piston pin outer diameter:22.000 mm (0.8661 in)
Piston ring side clearance:Top0.020-0.060 mm (0.0008-0.0024 in)
Second0.030-0.065 mm (0.0012-0.0026 in)
Oil0.020-0.060 mm (0.0008-0.0024 in)
Piston ring end gap:Top0.100-0.300 mm (0.0039-0.0118 in)
Second0.200-0.400 mm (0.0079-0.0157 in)
Oil0.250-0.500 mm (0.0098-0.0197 in)
Crankshaft journal diameter:60.000 mm (2.3622 in)
Crankpin diameter:45.000 mm (1.7717 in)

Cylinder head

The cylinder head is made of an aluminum alloy with good cooling efficiency. The M52TU B25 engine use chain-driven double overhead camshafts and four valves per cylinder. Standart head height is 140.0 mm (5.5118 in). The cylinder head employs a crossflow design for greater power and efficiency. Intake air enters the combustion chamber from one side while exhaust gasses exit from the other. This engine is equipped with double VANOS (Variable Camshaft Timing) system. VANOS is fully variable and operates independently on both intake and exhaust sides.

Intake valves are 33.0 mm (1.2992 in) in diameter and exhaust valves are 30.5 mm (1.2008 in), valve lift are 9.0 mm (0.356 in). Valve clearance is set by self-adjusting (zero-lash) hydraulic lifters for reduced valve noise and the elimination of routine valve adjustment.

Cylinder head
Cylinder head alloyAluminum
Valve Arrangement:DOHC, chain driven
Valves:24 (4 valves per cylinder)
Intake/Exhaust duration:244°/228°
Valve head diameter:INTAKE33.0 mm (1.2992 in)
EXHAUST30.5 mm (1.2008 in)
Valve steam diameter:INTAKE6.0 mm (0.2362 in)
EXHAUST6.0 mm (0.2362 in)

Head tightening procedure and torque specs:

  • Step 1: 40.0 Nm; 4.1 kg·m; 29.5 ft·lb
  • Step 2: Turn all bolts 90°
  • Step 3: Turn all bolts another 90°

Maintenance data

Compression pressure
Minimum10.0 kg/cm2 (9.9 bar, 145 psi) / 350 rpm
Compression differential limit between cylinders:1.0 kg/cm2 (1.0 bar, 15 psi) / 350 rpm
Oil system
Recommended engine oil SAE 5W-30
Oil typeBMW LL-98 or LL-01
Engine oil capacity (Refill capacity)~ 6.5 L (6.87 US. qt, 5.72 Imp. qt.)
Oil change interval, km (miles)5,000-10,000 (3,000-6,000)
Ignition system
Spark plugBosch: FGR7DQP, NGK: BKR6EQUP
Spark plug torque:25 N·m (2.5 kg·m, 18.4 ft·lb)

Vehicle applications

ModelYears Produced
BMW 323i, 323Ci (E46)1998-2000
BMW 525i (E34)1998-2000
BMW Z3 2.3i (E36/7 )1998-2000
BMW 323ti Compact (E36) – with single VANOS1999-2000
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