Lately I've been working on several 80's Mercedes diesels, and since these cars commonly rack up respectable odometer readings timing chain stretch is something that needs checked. It's a SOHC 5 cyl. turbo diesel with a double-roller timing chain maybe 2.5-3 ft. long - 5 degrees stretch is considered time for corrective action. Most people scoff at the idea of installing an offset woodruff key in the cam sprocket, but the FSM even outlines doing in cases of more moderate stretch. Replacing the chain isn't as bad a job as most engine (don't have to remove the front cover or anything) but it still at least doubles the cost of the job. If there's no unusual wear visible on the chain or guides, and stretch isn't severe (10* or more?) is it really that big a gamble to just install an offset key in a chain this stout?
OM617 timing chain opinions?
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Originally Posted By: supton
Is there a tensioner to take up slop?
Is wear (aka stretch) linear? As in, if it took 200k to hit 5 degrees, will it take 200k to hit 10 degree? I'm wondering if wear rapidly accelerates and it's just a matter of buying time.
I would assume no because as wear increases, so does play which theoretically would increase the rate of wear over time/ mileage.
Is there a tensioner to take up slop?
Is wear (aka stretch) linear? As in, if it took 200k to hit 5 degrees, will it take 200k to hit 10 degree? I'm wondering if wear rapidly accelerates and it's just a matter of buying time.
I would assume no because as wear increases, so does play which theoretically would increase the rate of wear over time/ mileage.
Originally Posted By: dlundblad
Originally Posted By: supton
Is there a tensioner to take up slop?
Is wear (aka stretch) linear? As in, if it took 200k to hit 5 degrees, will it take 200k to hit 10 degree? I'm wondering if wear rapidly accelerates and it's just a matter of buying time.
I would assume no because as wear increases, so does play which theoretically would increase the rate of wear over time/ mileage.
This is my thinking as well. I would replace the chain and do it right.
Originally Posted By: supton
Is there a tensioner to take up slop?
Is wear (aka stretch) linear? As in, if it took 200k to hit 5 degrees, will it take 200k to hit 10 degree? I'm wondering if wear rapidly accelerates and it's just a matter of buying time.
I would assume no because as wear increases, so does play which theoretically would increase the rate of wear over time/ mileage.
This is my thinking as well. I would replace the chain and do it right.
Yes, there is a spring-loaded plunger that acts on a shoe to keep the chain tight.
I'd replace the chain with rails, cam oiler pipe and not lose sleep over this. It seems to me the offset crank key is more of a kludge fix if a new chain doesn't restore things to factory spec or if something was off.
JHZR2
Staff member
The FSM absolutely allows for an offset key.
I'm in the do it right camp; not everyone wants to spend that money and energy though.
If it was a rust bucket 123 or 126 that had other issues, I'd likely consider an offset key, retiming the IP, and being done.
If it was a clean example. I'd do it right.
I'm in the do it right camp; not everyone wants to spend that money and energy though.
If it was a rust bucket 123 or 126 that had other issues, I'd likely consider an offset key, retiming the IP, and being done.
If it was a clean example. I'd do it right.
Appreciate the insight, thanks guys.
I can't remember the specs in the FSM, but I used a offset key in my OM617 engine that likely had 175k+ miles on it. I'd be comfortable with the largest key available. That said, a new chain isn't $$ or that complex to install.
I had a 300CD which I swapped in a 617 turbo and a 240D 4spd... I had the engine apart to replace the rear main seal, new HG, turbo drain seals, 4spd manual swap, etc. I'd ne more concerned with turbo play and injectors...
Those engines were stout, yes there's a right way to do things... but at that point you'll likely need injectors, IP rebuild, etc... Had the car for a few years and sold it. It was fun, cool and a learning experience... but I don't miss the outdated tech, noise, and comfort.
I had a 300CD which I swapped in a 617 turbo and a 240D 4spd... I had the engine apart to replace the rear main seal, new HG, turbo drain seals, 4spd manual swap, etc. I'd ne more concerned with turbo play and injectors...
Those engines were stout, yes there's a right way to do things... but at that point you'll likely need injectors, IP rebuild, etc... Had the car for a few years and sold it. It was fun, cool and a learning experience... but I don't miss the outdated tech, noise, and comfort.
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