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)
Cylinder block material	Cast Iron
Cylinder 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. In 1961, the engine capacity was increased to 2.0 L (1,988 cc) and power was uprated to 55 PS (40 kW) 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.

Models

Engine	Displacement	Power	Torque	Years
OM621 I	1.9 L (1,897 cc)	37 kW (50 PS) at 4,000 rpm	108 N⋅m (80 lb⋅ft) at 2,200 rpm	1958–1959
OM621 IV	2.0 L (1,988 cc)	35 kW (48 PS) at 3,800 rpm		1961–1962
OM621 III / VIII		40 kW (55 PS) at 4,200 rpm	118 N⋅m (87 lb⋅ft) at 2,400 rpm	1961–1968
	2.2 L (2,197 cc)	40 kW (55 PS) 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