That poor tensioner seems to get quite a workout from the belt and other things the belt pulls. For some reason, the tensioner on these engines just doesn't last the way it does on my GM engines. I think there may be two factors at work, 1) the diesel MB engine seems to put a lot more vibration and shock into the belt, and 2) the tensioner design seems mechanically weaker than other designs.

I broke a timing cover shortly after a tensioner and shock change on my 87 300D. The new shock was a LOT stiffer than the old one, and I feel it stressed the aluminum cover a lot more, resulting in it cracking and breaking open. The new timing chain cover has a stronger design, possibly due to this issue. I have yet to take the challenge to fix the car, but it needs to be done this year.

Since the design is weak, there is nothing you can do but watch it closely and when it goes out, replace the parts with quality parts.

Ken300D

Carfax is $25 for 30 days. Autocheck is $25 for 60 days.

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles