Jowl

I only recently became educated about the need to replace the timing chain on my 1991 420 sel. My 300D wagon (not a turbo) has 170K miles. Would I be smart to replace its timing chain?

H-townbenzoboy

First of all, you need to check the timing chain stretch. If it is over 5 degrees, either use an offset key to adjust back to proper specs, and if that doesn't work, replace it. If it's not over 5 degrees, leave it alone.

Rick I

I have a bit different opinon about replacing Diesel timing chains in the 617 engine. This is from many years of experience. That engine type has a greatly increased possibility of a timing chain break after it reaches 100,000 miles. I have worked on many which have broken the chain and they often have 130,000 to 160,000 miles. If the chain breaks, it occurs suddenly with no warning, has little relation to stretch, and the engine will most likely not be repairable, and may not even be good enough to use for a core.

If your engine is running good and you plan to continue to use it, it is very wise to have the timing chain replaced. The replacment can be done by only removing the valve cover and an experienced person can install it in 1 hour. This is cheap insurance.

KosherBenz

braverichard

I can understand your explained position on timing chains on 617s, but I know a guy who has worked on these MB diesels since 1974 and he says that most of them rarely need timing chains before 250-300,000 miles provided the engine oil was always changed on time. He explained details about the amount of stress put on the timing chains and how balanced the engines are to explain his observations. I'm not trying to say you're wrong, but I'm just showing that every one that claims to "know" these engines seems to have a different perspective on certain aspects of them. Indeed, you are right though that the cheap insurance to take out would be to simply replace the chain. But I say that if there isn't much stretch, keep the chain on!