OM615 chain stretch
 

I'm taking the head off my 73 220D, and as I was lining up the camshaft timing I naturally had a look to see what the chain stretch was - well it was 20+ degrees. I didn't even think that was possible with a diesel. Obviously something is wrong and assuming that the timing is correct is it easier to replace the chain after I have the rest of the engine back together, or while I have it apart? I am digging through my manual for OM615 chain replacement but haven't found it yet.

Thanks!

It is more than likely easier with the head on - less opportunity for slack in the wrong place in my opinion, but others may not agree. If the front of the engine came off all the way, like it does on the W201 190E, it is a different story. Jim

So is it safe to run at all with that amount of stretch? I'd like to see if it even works before I start putting new parts on it.

What do you mean by safe? Eventually the chain will fail. I believe that amount of stretch is beyond the range of the available offsets for Woodruff keys from MB, therefore I would assume it is beyond the allowable stretch. I have no idea if that means it is unsafe. Jim

I would think if your chain really has that much stretch you are very close to having valve, piston collision, :eek: which could be "terminal" to your engine.

I just mean, can I start the engine after I get it back together, drive it around the block to check out transmission, brakes, etc. - not extended highway use. If everything works, I'll keep on repairing.

I suppose I had better play it safe, when I was trying to set TDC (with the injectors removed), there was a lot more resistance at certain points than I thought proper for an engine with no compression (and assuming there is no bore damage from overheating). However I'll finish getting the head off today and see what the damage is. I expect to find the head is cracked anyway (there were some other signs of chronic overheating: no thermostat installed, cooling system full of crud, water bottles in trunk).

Safe? No way! 15 degress is the maximum amount of strect allowed with these chains and I would replace this right away even if it means you have to wait for this part to arrive!

I just bought a Wagon with the same problems as your 220D, but the owner thought it would be OK to take it out for a short haul to see if it ran ok and the timing chain broke, busted the crank in 3 pieces, snapped the sprocket off the camshaft and the whole mess dropped into the oil pan, but not before it was tossed into the oil pump drive chain and ripped it off the front of the oil pump breaking the shaft and stripping the pump sprocket!!!!:eek::eek:

I bought the car, a really nice rust free model 300TDT loaded with all options including a sunroof and a real nice interior for $500! Now I've got the engine out and apart and already spent $1200 on a new oil pump and other related parts, including a new timing chain!;) Thank god my camshaft is a lot easier to find than yours will be!:D

Take your time and do it right! Nothing is more expensive than a cheap Mercedes! And it will continue to be a cheap Mercedes if you start taking shortcuts!

I agree...this is indeed a cheap Mercedes, and I'm trying to be as cheap as possible repairing it but that's a dangerous shortcut I don't want to take. So new timing chain it is...

reread post #5:rolleyes:

oh I did :) I'll know just what's up once i get the head off. I am down to the little M8 bolts at the front, would have had it off yesterday but a storm rolled in.

Oh, your almost there, good The reason I responded to your "there was a lot more resistance" post, is because that happened to me when I hand turned one over and it would come up to a "slightly harder too get past", spot. I had the timing off. No harm:P,