Mercedes-Benz OM 300 (large)

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This article deals with six-cylinder diesel engines with a total displacement greater than 6 liters, the main application of which was medium and heavy trucks. The smaller-displacement four- and six-cylinder engines of the 300 series for light trucks are described under Mercedes-Benz OM 300 (small) .

Mercedes Benz
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OM 300 series
Production period:	1950-1970
Manufacturer:	Mercedes Benz
Working principle:	diesel
Motor design:	In-line engine
Displacement:	7.270-11.575 cm 3
Mixture preparation:	Pre-chamber injection and direct injection
Engine charging:	Partly turbocharged
Power:	92-250 kW
Dimensions:	780 - ??? kg
Previous model:	OM 67 series
Successor:	OM 400

The Mercedes-Benz OM 300 (large) series comprises several generations of six-cylinder engines, which were mainly produced for driving medium and heavy trucks . The origins of the previous OM67 design go back to the mid-1930s; the engines were replaced by the OM 400 series from 1970 .

History and Development

Immediately after the Second World War , the medium-weight L4500 truck was initially continued to be built unchanged. H. with the pre-war engine OM67 / 4 . In 1954 the engine was given the designation OM325 with unchanged displacement (and otherwise unknown changes); previously the OM315, with its larger displacement and more powerful, was derived from the pre-war engine. 1956 followed with the OM326, an even more powerful engine with four valves per cylinder.

Conversion to direct injection

Up until around 1963 the engines had pre-chamber, then direct injection . For normal truck use, the maximum power was last at 240  HP = 177  kW . From around 1970 the engines were replaced by the newly developed OM400 engines . In Brazil, at least the OM355 was built and even further developed.

Technical specifications

Engine type	built from	Design	Bore × stroke	Displacement	Combustion process	Power at speed and comments
OM67 / 4	1945	R6	105 × 140	7.270 L.	Antechamber	82 kW (112 PS) 2250 rpm, approx. 1952: 88 kW (120 PS)
OM315	1950	R6	112 × 140	8.272 L.	Antechamber	107 kW (145 PS) 2100 rpm
OM325	1954	R6	105 × 140	7.295 L.	Antechamber	92 kW (125 PS)
OM326	1956	R6	128 × 140	10.80 l	Antechamber	127–147 kW (172–200 hp), 4 valves / cylinder
OM326h		R6	128 × 140	10.80 l	Antechamber	Underfloor motor for buses
OM327	~ 1969	R6	112 × 140	8.27 l	Directly	125 kW (170 PS) 2400 rpm
OM346		R6	128 × 140	10.80 l	Directly	132 kW (180 PS), 149 kW (202 PS) (154 kW with switchable fan), 2200 rpm, 608/706 Nm
OM346h		R6	128 × 140	10.80 l	Directly
OM355	1967	R6	128 × 150	11.575 L.	Directly	169 kW (230 PS), from 1969: 177 kW (240 PS)
OM355A		R6	128 × 150	11.575 L.	Directly	206 kW (280 PS), only in Brazil
OM355LA	1988	R6	128 × 150	11.575 L.	Directly	250 kW (340 PS), only in Brazil
OM360	~ 1969	R6	115 × 140	8.72 l		125-141 kW (170-192 hp)
OM360h		R6		8.72 l

Nomenclature:
OM = oil engine = diesel engine
h = horizontal / lying for buses
A = (turbo-) charged
LA = (turbo-) charged with charge air cooling
~ = the year is the year of publication of the operating instructions, spare parts list or similar. This can vary considerably from the time the engine was built.

Maybe there was OM346A, but no reliable documents (mainly from Mercedes-Benz) could be found.