The OM603 doesn't have the ability to correct for timing chain elongation. There is no keyed shaft, they use a cam sprocket with an alignment hole instead. If the chain is stretched, replace it.

My SDL has 178K according to the odometer (I suspect more like 225K) and has 1˚ of chain stretch. Not sure if it's been replaced or not, nothing else has been, so I suspect it is original.

Chain wear is a function of maintenance, not mileage. Poor maintenance habits - crap oil, long change intervals, etc will cause the chain to wear faster.

Theoretically how long could a original chain last with great maintenance habits? Surely all chains and its surrounding parts have some kind of wear and eventually breakdown, but I've seen once or twice OM617s with 400,000+ miles on them with the original chain. It was no coincidence that those cars were maintained like a damn F16.

Ditto, for those w/ an 82-85 turbo-diesel. I pulled the lower oil pan on my 1984 and found a bolt that mounts the oil pump sitting in the bottom, along w/ part of that black plastic guide rail. I recall the snap ring was still on the shaft. The guide rail had cracked at the pivot hole and was cocked upwards, dragging on the chain.

Others say you must remove the upper oil pan to replace the oil pump, which means engine out of vehicle, but I was able to remove it just thru the small oil pan. Besides the oil pump, you must also remove the front bearing block. Replace the O-rings on the oil pump outlet tube and check the bearing while in there. A new guide rail was cheap.

I am at 233K on my 617. I am pricing the job now.:)

617.952
Besure the Machanic installs a IWIS/JIWIs timing chain.

Also the Timing Chain Tensioner spring often has coils with metal worn off on the sides. Good Idea to replace that.

214k on a W124
 

I have 214k on my 1991 300d. Original chainS (plural).