Mercedes-Benz M121 engine

The Mercedes-Benz M121 was a single overhead camshaft inline four-cylinder engine that Mercedes-Benz introduced in 1955. It was based on the M180 six-cylinder engine, which had appeared three years earlier, and replaced the overhead valve M136 that had been in production since 1935. Its first application was the W121 190 SL roadster in May 1955, and from 1956 until the end of 1967 it powered the entry level 180, 190 and 200 series of the W120, W121 and W110 sedans. A diesel version, the OM621, was built alongside from 1958 and shared many components. The M121 was developed in the Sindelfingen works by a team led by Hans Scherenberg, and it was modernised in 1968 as the M115.