Mercedes-Benz M108 engine

The Mercedes-Benz M108 is a 2.5 litre single overhead camshaft inline-six that Mercedes-Benz fitted to its W108 saloons from September 1965, and a member of the M180 family of engines. It was made by stroking the 2.3 litre M180 by 6 mm to a bore and stroke of 82 mm by 78.8 mm, which raised displacement to 2,496 cc. Carrying the extra output called for seven main bearings in place of four, a larger oil pump, larger ports and valves enlarged by 2 mm. The first version, the M108 I, kept the twin two-barrel Zenith carburettors and 9.0:1 compression of the later M180 and gave 130 hp at 5,400 rpm in the 250 S. Its fuel-injected sister, the M129, proved short lived, and the family block was redesigned with symmetrical cylinder spacing as the M114.