Timing case

The flywheel housing forms the rigid connection between the engine block and the clutch or transmission assembly of MAN and Mercedes trucks, buses and vans. This casting, also known as a clutch housing or rear engine housing, centres the gearbox in relation to the crankshaft and protects the flywheel, clutch and starter ring gear against external contamination. On vehicles with manual, automated or automatic gearboxes, flywheel housings differ in bolt pattern, centring, sensor connections and design for a single-mass or dual-mass flywheel. Correct identification based on the chassis number is therefore mandatory; visual comparison or selection based solely on the model name is never sufficient.

Flywheel housings are fitted to a wide range of engine families, including MAN D08, D20, D26 and D38 engines and Mercedes OM 906, OM 457, OM 470, OM 471 and OM 473 engines. The version is determined not only by the engine, but also by the fitted gearbox, clutch concept, starter motor and any PTO configurations. The same engine family may therefore use different rear engine housings.

The housings are generally manufactured from cast aluminium or cast iron. Aluminium versions reduce weight, while cast-iron variants offer high rigidity and resistance to thermal loads. The machined locating bores, dowel pins and flatness of the mating surfaces with the engine block and transmission are critical. Even a minimal deviation in coaxiality can lead to excessive load on the release bearing, input shaft bearing, crankshaft thrust bearings or gearbox input shaft. The mounting surfaces for the starter motor, crankshaft sensor, inspection cover and rear crankshaft oil seal must also be undamaged and dimensionally stable.

Cracks around starter mountings, stripped threaded holes, worn locating bores and distorted mounting surfaces are common defects. They often occur after incorrect transmission installation, a loose gearbox bolt, a broken engine mount, a defective dual-mass flywheel or repeated starting with a poorly engaging starter motor. A crack in the housing can cause resonance noises, starting problems or engine oil leakage through the rear crankshaft oil seal. Please note: oil in the clutch housing does not automatically indicate a defective seal; damage to the seal seating surface or a distorted flywheel housing may also affect the seal.

First clean the entire mating area and locate leaks using UV dye or talcum powder. Then visually inspect the bolt holes, locating bushes and mating surfaces for cracks, corrosion and thread damage. Measure the flatness of the engine-side and transmission-side mounting surfaces using a straightedge and feeler gauge. Always compare the measured deviation with the manufacturer's tolerance. Also check the centring of the clutch housing using a dial indicator on the crankshaft flange or reference bore. Radial or axial deviations outside specification require investigation for a distorted housing, missing dowel pins or damage to the engine block.

Replace a flywheel housing in the event of structural cracks, distortion, worn locating holes or irreparable starter mountings. Welding is only justified when the material type, crack area and post-treatment have been technically assessed; replacement is generally the reliable solution for load-bearing centring and mounting areas. Always install using the correct dowel pins, new fastening bolts where specified, and the prescribed tightening torque plus angle. During disassembly, also inspect the dual-mass flywheel, clutch, starter ring gear, rear crankshaft oil seal and input shaft guide. This prevents a new housing from being damaged again by an underlying alignment or driveline fault.

Braem can assist with chassis-number-based selection of suitable new or used flywheel housings and with the assessment of associated engine and transmission components.