The OM621 is an

inline-four A straight-four engine (also referred to as an inline-four engine) is a four-cylinder piston engine where cylinders are arranged in a line along a common crankshaft. The majority of automotive four-cylinder engines use a straight-four layout ( ...

diesel engine The diesel engine, named after the German engineer Rudolf Diesel, is an internal combustion engine in which Combustion, ignition of diesel fuel is caused by the elevated temperature of the air in the cylinder due to Mechanics, mechanical Compr ...

produced by

Mercedes-Benz Mercedes-Benz (), commonly referred to simply as Mercedes and occasionally as Benz, is a German automotive brand that was founded in 1926. Mercedes-Benz AG (a subsidiary of the Mercedes-Benz Group, established in 2019) is based in Stuttgart, ...

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

camshaft A camshaft is a shaft that contains a row of pointed cams in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition syst ...

cylinder head In a piston engine, the cylinder head sits above the cylinders, forming the roof of the combustion chamber. In sidevalve engines the head is a simple plate of metal containing the spark plugs and possibly heat dissipation fins. In more modern ...

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder (engine), cylinder a ...

s, 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 The Unimog (pronunciation in American English: ''YOU-nuh-mog''; British English: ''YOU-knee-mog''; German: , ) is a Daimler Truck line of multi-purpose, highly offroad capable AWD vehicles produced since 1948. Utilizing engine-driven power tak ...

vehicles until 1988.

Models

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

{{reflist, 30em OM621 Diesel engines by model Straight-four engines