Mercedes-Benz OM621 engine

The Mercedes-Benz OM621 is an inline-four diesel engine that Mercedes-Benz produced from 1956 to 1968 in displacements of 1.9, 2.0 and 2.2 litres. It followed the OM636 and was succeeded by the OM615. The design is based on the petrol M121 engine but with revised camshafts, cylinder head, pistons and fuel injection system. In 1961 the capacity grew to 2.0 litres (1,988 cc) and output to 55 PS for the newly introduced W110 models. After the OM615 took over in cars, a 2.2 litre (2,197 cc) version of the OM621 stayed in use solely in Unimog vehicles until 1988. Listed applications include the W121 190D, the W120 180Dc, the W110 190Dc and 200D and the Unimog 421.