Mercedes-Benz OM621 engine

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.

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 (48–54 PS; 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 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.^[2]

Models

Engine	Displacement	Power	Torque	Years
OM621 I	1.9 L (1,897 cc)	37 kW (50 PS; 50 hp) 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; 47 hp) at 3,800 rpm		1961–1962
OM621 III / VIII		40 kW; 54 hp (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; 54 hp (55 PS) at 3,000 rpm		1966–1988

OM621 (37 kW version)

37 kW (50 PS; 50 hp)

• 1958–1959 W121 190D, 190Db

OM621 (35 kW version)

35 kW (48 PS; 47 hp)

• 1961–1962 W120 180Dc

OM621 (40 kW version)

40 kW (54 PS; 54 hp)

• 1961–1965 W110 190Dc
• 1965–1968 W110 200D
• 1966–1988 Unimog 421