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English   The birth of a legend: the 300 engine series - first unveiled in 1949 - is a major advancement
12.05.2009 von admin

This phase in the history of the 300 series played a major part in establishing the excellent reputation of the 300 series engines. Lengthy experiments on various combustion systems produced a more or less centred four-hole injection nozzle at an angle of 30 degrees, and a cylindrically configured combustion chamber in the piston. The bore and stroke, and thus also the 5.675-litre displacement of the six-cylinder engine, originated from the OM 322.

The engine was available in several performance variants, developing 100, 110 and 126 (and later 130) hp. Greater efficiency and improved combustion reduced the thermal load compared with predecessor engines. The higher ignition pressure of 80 bar instead of 60 bar presented no problems for the engines. The new units soon gained an excellent reputation and replaced the OM 312, OM 321 and OM 322 pre-combustion engines.

Advent of the first four-cylinder engines with direct injection

In tandem with the six-cylinder engines with which they had been developed concurrently, Daimler-Benz presented for the first time four-cylinder engines bearing the model designation OM 314. They had a displacement of 3.78 litres and a power rating of 80 hp, later 85 hp. Like their larger brothers, they were used in the new cab-over-engine vehicles of the LP series. The engines series also subsequently found use in the company’s large-capacity vans, which were christened “Düsseldorfer” after their production location, in the small O 309 bus, a derivation of the Düsseldorfer, in the Unimog and in the MB-trac agricultural vehicle.

Mercedes-Benz O 309.

Inevitably, the large four-cylinder engines did not possess the smooth running characteristics of the six-cylinder engines, and in this case the long stroke design proved a serious drawback. Developer Körner’s generous assessment was that “it was not a sophisticated engine”. Even though the engineers were successful in trying to tame the engine using two balancer shafts, the cost involved militated against this additional measure. “It would have been unreasonably expensive,” was Körner’s realistic appraisal of the situation. On the other hand, after brief initial problems, the four-cylinder achieved a reputation for excellent reliability – it just went on and on.

In the meantime, Daimler-Benz was also obliged to increase the power rating of the OM 352. First came the OM 352 A (the ‘A’ stood for Aufladung, turbocharging) for snow clearance machinery. This was also used in trucks from the latter half of the 1960s, with power ratings of 150 and 156 hp. The turbochargers were initially supplied by Eberspächer, then by Garrett and also KKK. During this period the power rating was increased initially to 168 hp and then to 172 hp. The OM 352 was the first turbocharged engine to win full acceptance from customers. A turbocharged version of the four-cylinder, the OM 314 A, also went into small-scale series production.

Development of turbocharged engines with intercoolers commenced in the mid 1970s. Once again it was the 300 series that led the way: the OM 362 LA, developing 192 hp, went into series production in the early 1980s with an unchanged displacement of 5.675 litres.

The OM 352 A was used in the cab-behind-engine truck, the various angular and rounded LP models and also in the New Generation (NG) vehicles. In addition, it made a name for itself as an industrial engine, both naturally aspirated and turbocharged. On the international market it has enjoyed a long career in Iran, where to date around 180,000 engines have come off the assembly lines. In 1981, production also started under licence in South Africa at Atlantis-Diesel-Engine (ADE).

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