Mercedes-Benz W124 cylinder head overhaul: what to check and replace
What should be replaced during a Mercedes-Benz W124 cylinder head overhaul?
The head bolts should be replaced, as the old ones may be corroded. In addition, the top-end gasket set is replaced and the valve guides are checked. On a diesel the glow plugs are replaced at the same time, and the coolant, oils, oil filter and breather hose rubbers are renewed.
What is the head bolt tightening procedure for the Mercedes-Benz W124 M104 engine?
On the M104 the bolts are tightened first to 55 Nm, then 90 degrees and another 90 degrees. For other engines, the values and the bolt length dimensions are found in the factory service manual.
How far may a valve be recessed and how is the seat checked?
On the OM603 diesel the valve head may be at most 0.9 mm below the head surface, measured with a straight edge and feeler gauge. Otherwise the valves are replaced. A good seat width is about 2 mm; if it falls at the edge, the seats are replaced.
How are the hydraulic valve lifters handled in a head overhaul?
The lifters are not washed, but kept in disassembly order and protected from dust. New lifters are filled with oil. The camshaft bearing caps are tightened evenly, and the sliding surfaces are lubricated before assembly.