Mercedes-Benz OM621 engine

The OM621 is an inline-four diesel engine produced by Mercedes-Benz, from 1956 to 1968. It was succeeded by the OM615 engine.

Mercedes-Benz OM621
Overview
Manufacturer	Mercedes-Benz
Production	1956–1968
Layout
Configuration	Inline-four engine
Displacement	1.9 L (1,897 cc) 2.0 L (1,988 cc) 2.2 L (2,197 cc)
Cylinder bore	85–87 mm (3.35–3.43 in)
Piston stroke	83.6 mm (3.29 in)
Block material	Cast Iron
Head material	Cast Iron
Valvetrain	SOHC
Compression ratio	18.0:1
Combustion
Fuel system	Indirect injection
Fuel type	Diesel
Cooling system	Water cooled
Output
Power output	35–40 kW (47–54 hp)
Torque output	108–118 N⋅m (80–87 lb⋅ft)
Chronology
Predecessor	Mercedes-Benz OM636 engine
Successor	Mercedes-Benz OM615 engine

Design

The OM621 is based on the petrol M121 engine, but features revised camshafts, cylinder head, pistons, and fuel injection system.[1] In 1961, the engine capacity was increased to 2.0 L (1,988 cc) and power was uprated to 40 kW (54 hp) for use in the newly introduced W110 models. After being replaced by the OM615, a 2.2 L (2,197 cc) updated version of the OM621 engine was used solely in Unimog vehicles until 1988.[2]

Models

Engine	Displacement	Power	Torque	Years
OM621 I	1.9 L (1,897 cc)	37 kW (50 hp) @ 4,000 rpm	108 N⋅m (80 lb⋅ft) @ 2,200 rpm	1958–1959
OM621 IV	2.0 L (1,988 cc)	35 kW (47 hp) @ 3,800 rpm		1961–1962
OM621 III / VIII		40 kW (54 hp) @ 4,200 rpm	118 N⋅m (87 lb⋅ft) @ 2,400 rpm	1961–1968
	2.2 L (2,197 cc)	40 kW (54 hp) @ 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

1. Long, Brian (2014-01-31). Mercedes-Benz 'Fintail' Models: The W110, W111 and W112 Series. Crowood. ISBN 9781847976048.
2. "1964-1993". www.mercedes-benz.co.uk. Retrieved 2018-07-22.