There is only 1 MB engine that MB suggested close inspection & replacement of the timing chain..the 1981-83 3.8L V-8 engine.

WHAT MB says on all other cars is to inspect the timing chain for stretch any time the valve cover(s) is removed.

More than 4-5 degrees of stretch on a GAS motor & the chain should be replaced.

And more that 3 degrees on a diesel motor.

YES the tensioner is the MOST common problem that causes the chains to stretch & break. Any plastic rail should be replaced!

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