Mercedes-Benz OM646, OM647 and OM648 engines (2002-10)

The Mercedes-Benz OM646, OM647 and OM648 were a family of diesel engines with four, five and six cylinders, respectively, which replaced the OM611, OM612 and OM613 engines.

Each OM646, OM647 and OM648 engine had am 88.0 mm bore and 88.3 mm stroke, a cast iron block, alloy cylinder head, second-generation Bosch common-rail direct injection (operating at up to 1600 bar), variable geometry turbocharger (VGT or VNT), an air-to-air intercooler, double overhead camshafts (chain-driven), four valves per cylinder (actuated by tappets), a compression ratio of 18.0:1, an electronically-controlled exhaust gas recirculation valve and an electric fuel pump.

Like their predecessors, pilot injection injected and burnt a small amount of fuel in the cylinder prior to combustion to pre-heat the chamber for faster warm-up and to better maintain temperature and pressure through the combustion cycle. More powerful versions of these engines were also fitted with a Lanchester balancer shaft which rotated in opposite directions at twice the speed of the crankshaft.

OM646 EVO

Introduced in 2006, the OM646 EVO engine effectively replaced the OM647 and OM648. Compared to the original OM646 engine, ninety (90) components were modified for the OM646 EVO. Changes included:

• shorter connecting rods for a lower compression ratio of 17.5:1;
• new turbochargers and modified intercoolers;
• a redesigned air duct; and
• ceramic glow plugs (previously metal) for improved engine starting and cold running behaviour.