The OM621 is an inline-four diesel engine produced by Mercedes-Benz from 1956 to 1968, variously in displacements of 1.9 L (115.8 cu in), 2.0 (121.3 cu in), and 2.2 L (134.1 cu in). It was preceded by the OM636, and succeeded by the OM615.
Design The OM621 is based on the petrol M121 engine, but features revised camshafts, cylinder head, pistons, and fuel injection system. In 1961, the engine capacity was increased to and power was uprated to for use in the newly introduced W110 models. After being replaced by the OM615, a updated version of the OM621 engine was used solely in Unimog vehicles until 1988.
Models EngineDisplacementPowerTorqueYearsOM621 I at 4,000 rpm at 2,200 rpm1958–1959OM621 IV at 3,800 rpm 1961–1962OM621 III / VIII at 4,200 rpm at 2,400 rpm 1961–1968 at 3,000 rpm 1966–1988
OM621 (37 kW version)
1958–1959 W121 190D, 190Db
OM621 (35 kW version)
1961–1962 W120 180Dc
OM621 (40 kW version)
1961–1965 W110 190Dc 1965–1968 W110 200D 1966–1988 Unimog 421
References