Mercedes M129 Petrol Engine Manuals

Mercedes Benz six-cylinder M129 2.5 liter 2,496 cc petrol engine was enhanced by fuel injection producing 150 horsepower, and was manufactured from 1965 to 1968

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Download: Mercedes Benz M129 Engine Service Manual

Mercedes M129 Engine Repair Manual
Download: 86.9mb, 911 pages, .pdf
Application: W108, W111, W113

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See Multi Unit Engine Manual Applications M108, M127, M129, M189

Download: Mercedes Benz M129 Engine Parts Manual

M129 Engine Exploded Parts Picture Catalog
Download: 1.45mb, 15 pages, .pdf

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M129 Engine Technical Data

The Mercedes M129 was derived from the M180 engine having its stroke increased by 6 mm (0.24 in) resulting in a bore of 82 mm and stroke of 78.8 mm. The M129 engines displacement of 2.5 liters (2,496 cc) was enhanced by fuel injection producing 150 horsepower. This fuel-injected M129 motor was used in the in the W108 and W111 250SE as well as the W113 250SL and produced an additional 20 hp over its carbureted relative the M108 in the 250S. The mechanically controlled six-piston fuel injection pump is what designated the variant as engine type M129.

With the addition of fuel injection, additional modifications included an increase from four to seven main bearings, a larger capacity oil pump, cylinder heads incorporating larger ports with 2mm (0.079 in) valve diameters, and slightly modified connecting rods reflecting a 6mm (0.24 in) longer stroke in a block of unchanged overall height. These modifications allowed the M129 to produce a resulting increase in power.

These M129 fuel injected cars used a six-plunger pump with injectors repositioned to give a more direct angle towards the heads inlet valves. The engine cooling fan was increased to six blades instead of four and incorporated a viscous coupling which engaged the fan when engine speed exceeded 3,000 rpm or the radiator water temperature reached a preset limit. While the M108 and M129 engines were relatively the same, only the fuel injected variants that were implanted in the W108 and W111 250 SE models along with the W113 250SL where designated M129 engines, with the carbureted W108 250S engine being designated the M108.

M129 Engine Faults

Like the M108 engine, the M129 injection engine was also criticized for its accumulation of engine damage due to thermal problems that evolved from three pairs of cylinders having unequal spacing, along with a longer piston stroke. Running at sustained high speeds, or under heavy load before warming up could cause these engines to be thermally overwhelmed creating overheating damage and wear. However, these motors when operated cautiously without heavy load can still be very reliable. Due to these potential issues, the M 108 and M 129 motors were only in production for a short time..

M129 Engine Applications:

W108 250SE 1965-1968
W111 250SE 1965-1967
W113 250SL 1966-1968

Mercedes M129 Vehicles
Series	Model	Years	Engine	Production	hp
W108	250SE	1965-1968	129.980	1965-1968	150
W111	250SE	1965-1967	129.980	1965-1968	150
W113	250SL	1966-1968	129.982	1965-1968	150

Engines Covered in this Multi Unit Manual

While this multi unit manual covers all engines listed here, it is recommended that the linked manuals below be used for those specific motors