All-round state-of-the-art engineering

Simply adding an extra feature such as an intercooler to the existing engines, as had been done in the case of the 192 hp OM 362 LA in 1983 (the unit that shared identical dimensions to the OM 352 A) would not have been a viable solution in the long term. The engineers therefore decided to redesign the combustion chamber, using spiral instead of swirl downdraught inlet ports. Inlets and outlets were all arranged on the left of the vehicle so as to eliminate long ducts with turbocharged engines. The housing was simplified and at the same time redesigned using ribs and thicker walls to enable it to cope with higher loads. Forged integral counterweights on the crankshafts and a modified hardening process on the crankshaft bearings and big-end bearings also provided for a high load capacity.

The pistons now featured only three rings with a barrel-shaped microsection that was highly resistant to scuffing. In addition to numerous other changes, there was also a new lubrication system and splash cooling was added for the turbocharged engines. The new OM 364/366 model series arrived in 1983/1984 to an enthusiastic reception: it was the birth of the most advanced engine series for the mid-range performance class of the day.

The engineers even paid attention to attractive packaging. To begin with, the engine specialists wanted to use the in-house designers led by Bruno Sacco, but that would have proved too expensive. Instead, the engineers tackled the job themselves, giving the engines a highly elegant exterior to go with their new inner qualities. They managed to push the power rating of the six-cylinder engine up to 200 hp, and later even to 240 hp. The four-cylinder started off as a naturally aspirated engine developing 90 hp, but from 1986 with the help of a turbocharger it developed 115 hp, meaning it could be used in the 711 D and 811 D large capacity vans.

Still able to meet Euro 2 standards

At some point, however, even the best model series in the world exhausts development possibilities. As Körner, the series developer, explained: “We could have developed the 300 model series further, but then we would have needed a new crankcase.” Any further refinement of these engines would have involved an unjustifiable expense. Furthermore, ingenious developments such as multivalve technology and constant throttle could not have been incorporated into the 300 series, and even the production machinery itself was getting old.

Nevertheless, as the OM 364 LA developing 136 hp, the four-cylinder engine unveiled at the RAI congress centre in Amsterdam in 1994 easily complied with the Euro 2 emissions standards that were to come into force from 1996. The features that made it more eco-friendly included an intercooler, a turbocharger with wastegate, a redesigned combustion chamber and five-hole instead of four-hole injection nozzles, as well as a higher injection pressure. In much the same way, the technology in the six-cylinder OM 366 LA changed in 1991 with its adaptation to meet Euro 1 standards. Thereafter, it had a maximum engine power rating of 240 hp. Additionally, intercooling (German abbreviation ‘L’) and turbocharging (German abbreviation ‘A’) made it generally possible to reduce the rated engine speed once more: the LA engines now required only 2600/min to develop their maximum output. This not only helped reduce fuel consumption and noise, it also extended the engines’ life expectancy.

A worthy successor in sight

Despite all this, however, the introduction of the Euro 3 emissions standard sounded the death knell for the long-serving 300 model series, which had proved its worth in so many different fields, from vans, trucks and buses to forklift trucks, power generators and special-purpose vehicles such as the Unimog and MB trac. Its successor was unveiled in January 1996 (initially in the LN 2) as the new 900 engine series which, with strokes of 102 and 133 millimetres, resulted in displacements of 4.2 litres (four-cylinder version) and 6.4 litres (six-cylinder version) respectively.

With three valves per cylinder (two inlet valves and one outlet valve), and electronically controlled pump-line-nozzle elements, they were well equipped to meet the upcoming Euro 3 standard, and even today, thanks to SCR technology, they have no problem meeting the Euro 5 standard. The 900 engine series has demonstrated its quality around the world as a truly global engine, and in this respect is a worthy successor to the 300 series engines, many of which are still engaged in active service in various parts of the world: indeed it is still possible to get hold of an OM 366 LA with 211 hp in the Brazilian cab-behind-engine L-1620 Classic.

Photos:
Daimler AG
Omnibusarchiv
Text:
Daimler AG