This chain stretch thing has been discussed many times with no conclusions except for the OM602 and OM603. Now before some smart ass concerned with syntax corrects me by telling me that chains don't stretch, I'm well aware of that. The metal wears, but chain stretch is the vernacular we are all familiar with. That being said, I have researched this subject for many hours looking for specs. I have a large bookcase stuffed with all the factory manuals dating back to when I used to service Gullwings at the dealership. I even have most of the factory service microfich, but have never seen a spec for the V/8s or the 4 and 5 cylinder diesels. I have asked on this forum and never got a response. Gilly and I even discussed it with no definitive answer. The only engines that MB gives specs for are the OM 602, 603. The book says replace the chain at 10 degrees. All the other manuals say to install a new chain if chain wear is beyond the limit, but that limit is never given. I have decided on a bench mark of 10 degrees on the V/8s. If my inspection shoed 8 degrees I would install a new chain, but 10 degrees is the absolute limit. The chain in the 4 and 5 cyl diesels is the same chain for all models and doesn't seem to stretch much if the vehicle is well serviced. I'm convinced that the valve train failure in the V/8s is because that long chain gets to whipping, and snaps off the inside rail on the left bank. The broken piece jams into the cam gear and the chain slips on the clogged gear teeth. The pistons keep going, but the cam doesn't, ergo, bent valves left bank. The problem is complicated by the fact that MB chose to hold the head down with steel bolts into aluminum. They could have used inserts. THe threads generally pull out requiring the installation of 18 heli coils per head. In 86 with the advent of the 420 and 560, they used expensive special bolts that seems to have corrected the problem. Anyway if anyone has comments, feel free.


Peter

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