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Old 10-29-2002, 10:14 PM
suginami suginami is offline
Join Date: Dec 2001
Location: Southern California, U.S.A.
Posts: 8,503
The chains do stretch on these M116 and M117 engines over time, because the chains are long and change direction many times as they travel from the crank at the bottom up to each cam on each side of the "V".

Most members and techs on this site recommend replacing the chains approximately every 100,000 - 120,000 miles. 4 degrees of stretch is considered the time to change the chain.

Further, it's more than just a loose chain that's the problem. The chain guide rails are made of plastic, and become hard and brittle over time, as well. As the chain stretches, it becomes loose, and starts to rattle and bang and slap against the guides. It usually happens at start-up, but when the chain gets loose enough and the guide rails are old and brittle enough, the chain will slap against the plastic and it'll break apart. Plastic pieces will get stuck in the chain and the sprocket, and bam!, you've bent a camshaft, pistons will hit valves, etc.

I've found from reading posts on this site, that's it's more often a loose chain breaking old guide rails, than a loose chain jumping a sprocket that causes an engine failure.

Your car may or may not be due for a timing chain replacement. But at minimum you should replace the upper guide rails.
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".