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The BMW M50 inline 6-cylinder engine was used in BMW models like the E34 5 Series Sedan and the E36 3 Series. The successor to the M50 was the M52 engine.

The M50 was produced in 2.0 (M50B20) and 2.5 liter (M50B25) configurations. A "Technical Upgrade" was issued in 1992 when the M50 because BMW's first engine to utilize the VANOS technology. Engines with a designation of M50TU are VANOS engines.

The M50 was a 24-valve engine utilizing BMW's 4-valve per cylinder technology. For each of the two camshafts, the bearings and the bucket-type tappets, with integrated hydraulic clearance adjustment, were carried in a demountable aluminum tappet block that was attached to the head by the same studs that held down the caps for the cam bearings. When this was removed there was good access to the cylinder-head bolts, despite the short cylinder spacing and the narrow valve angle (39.5 degree included angle). The exhaust camshaft was driven by a single-row chain. From a smaller sprocket and another single-row chain, the exhaust cam drove the inlet cam, an arrangement that reduced the engine's installed height.

The intake system was made entirely of reinforced plastic using the core melt-out procedure. This was the world's first mass-production application of this technology. The belt-driven intermediate shaft previously used to drive the distributor and the oil pump, was dispensed with. The oil pump was not driven by a short chain from the crankshaft, as was the case in the M10 engine. Ignition was by a new system with an individual ignition coil for each cylinder, known as "static high-voltage distribution."

Like its predecessor the M20, the M50's cylinder center distance was 91 mm. M20 bore and stroke dimensions were also kept for the 2.0 and 2.5-liter versions, for which power output was 150 bhp and 192 bhp respectively. The engine was designed for Super petrol. Until this time, engines for catalytic converters had been designed for use with Regular unleaded in accordance with its wider availability.

In 1992 production began of further-developed versions of this engine which offered lower fuel consumption and increased torque. At the same time, the new evolutions contributed to a reduction in exhaust emissions and a further improvement in the engine's running characteristics. A key role was played by the VANOS variable-cam-timing system, which made a positive contribution to all four criteria.

Measures were taken to reduce friction in the valve gear and pistons. As well, the use of the longest possible connecting rods for each capacity optimized fuel consumption and enhanced smooth running. The use of electronic knock detection also contributed.


Engine Codes  Engine Specifications
Item/Measurement M50B20 M50B20 M50B25 M50B25
Vehicle 520i 520i 525i 525i
Number of Cylinders 6 6 6 6
Layout in-line in-line in-line in-line
Installation 30° inclined right 30° inclined right 30° inclined right 30° inclined right
Coolant liquid liquid liquid liquid
Crankcase/Block Material perlit. cast iron cast iron perlit. cast iron cast iron
Crankshaft one-piece one-piece one-piece one-piece
Main Bearings 7 7 7 7
Weight (kg) 194 198 194 198
Valve Layout dohc dohc dohc dohc
Camshaft Drive simplex chain simplex chain simplex chain simplex chain
Camshaft Bearings 7 each 7 each 7 each 7 each
Valves per Cylinder 4 4 4 4
Cylinder Center Distance (mm) 91 91 91 91
Displacement (liters) 1.991 1.991 2.494 2.494
Bore/Stroke (mm) 80/66 80/66 84/75 84/75
Stroke/Bore Ratio 0.83 0.83 0.89 0.89
Piston Speed (ms) 13.0 13.0 14.8 14.8
Valve Timing (IO/IC) 24°btdc/36°abdc 9°btdc/39°abdc 19°btdc/41°abdc 4°btdc/44°abdc
(EO/EC) 38°bbdc/10°atdc 39°bbdc/9°atdc 35°bbdc/13°atdc 35°bbdc/13°atdc
At Valve Lift (mm) ER-ER ER-ER ER-ER ER-ER
Valve Lift I/E (mm) 9.7/8.8 9.0/9.0 9.7/8.8 9.0/9.0
Connecting Rod Length (mm) 135 145 135 140
Connecting Rod Ratio r/l 0.24 0.23 0.28 0.27
Compression Ratio 10.5:1 11.0:1 10.0:1 10.5:1
Fuel Super LF Norm-Sup Plus LF Super LF Norm-Sup Plus LF
Power Output (bhp@rpm) 150/5900 150/5900 192/5900 192/5900
Power per Liter (bhp/liter) 75.34 75.34 76.98 76.98
Power/Weight Ratio (kg/bhp) 1.29 1.32 1.01 1.03
Torque (mkg@rpm) 19.4/4700 19.4/4200 25/4700 25.5/4200
Torque per Liter (mkg/liter) 9.73 9.73 10.01 10.22
Mixture Preparation fuel injection fuel injection fuel injection fuel injection
 Maker Bosch Siemens Bosch Siemens
 Designation DME M3.1 DME MS41 DME M3.1 DME MS41
Ignition integrated integrated integrated integrated
Ignition Advance map map map map
Generator 12 V/1120 W 12 V/1120 W 12 V/1260 W 12 V/1260 W
Supercharging - - - -
Miscellaneous - VANOS, KD - VANOS, KD
Year of Introduction 1989 1992 1989 1992

source: BMW Motoren, Dr. Karlheinz Lange



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More engine links.

BMW E36 M3 CSL Lightweight had an M50 engine.

Story of an engine swap: M50 engine into popular E30 body style.

M50 engines use a water pump with a plastic impeller. After 80k this can fail and leave little bits all around the cooling system. Replace it with the later metal style pump before it fails. M50s don't seem to like the cooling system being neglected, you need a fluid change every 2 years at least. - John G. Burns

John G. Burns E36 page has some tips for M50 engines.

Koala Motorsport page on M50 overheating has a procedure for replacing the water pump.

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