M108

When the W 108 arrived in September 1965 Mercedes-Benz needed a 250, and got there by lengthening the stroke of the 2.3-liter M180 six by 6 mm to 78.8 mm. The extra capacity forced a structural change rather than a bolt-on one: the crankshaft went from four main bearings to seven so the engine would stay smooth at the higher output, with a larger oil pump, bigger ports and valves 2 mm larger to feed it. Underneath, the design still traced back to Wolf-Dieter Bensinger’s six of 1951.

In this form — twin two-barrel Zenith 35/40 INAT carburetors, 9.0:1 compression, 130 hp at 5,400 rpm — it was the entry engine of the W 108 range, one rung below the fuel-injected M129 of the 250 SE. It went into nothing else, before or after. The 250 S ran from September 1965 to March 1969 and found 74,677 buyers, a substantial number for an engine built to serve a single model, and it stopped when the 2.8-liter M130 and the 280 badge replaced it.