How do you tell when the timing chain needs to be replaced? I could find nothing in the official MB repair manual. It seems there would be a dimension on how far the chain tensioner projects that would tell when to replace chain. Can anybody tell me this dimension or another way to determine when the timing chain is worn beyond limits? Engine 1980 617.950
P.E.H.

My wife's car is a 1983 300SD. I replaced the chain at 358,000 miles. Inj. pump timing was off by 6 deg. Performance was really off. After the change it was like a new car.

You can have it checked with the valve cover off. You line up the marks and read the degrees off of the balancer. Mercedes says more than 3 and you have a problem on a Diesel.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
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Just had the valves adjusted on the 81 SD at 190,000 miles - chain is fine.
From what I can gather, 300,000+ miles on the original chain is not uncommon with routine maintenance.
Valve adjustment, which should be performed every 15,000 miles on your particular engine, is when the chain can be checked for stretch.