M121

The 1.9-liter overhead-camshaft four was a fresh design, and its first job was the 190 SL — the touring sports car Hoffman wanted in American showrooms beneath the 300 SL. Injection was ruled out on cost, so after trials of SU, Weber and Solex hardware the production cars took two Solex 44 PHH flat-stream carburetors and 105 PS. Those carburetors became the model’s known weakness: the throttle spindles wear, the idle drifts, and putting it right has never been cheap. In 1956 the same engine, detuned to 75 PS, went into the 190 saloon.

That saloon mattered more than the figure suggests. The 180 alongside it still used the side-valve M136 of 1936, with its ragged combustion chambers and matching thirst; the M121 brought a chain-driven overhead camshaft and rocker fingers to the small Mercedes, and by 1957 the 180 had a 65-PS version of it as well. Early engines ran on only three main bearings and were rough for it. Five bearings and two liters came in 1965 with the 200, along with the first constant-depression Stromberg carburetor Daimler-Benz had used — and a good deal of early complaint about it.