The question should have been, has anyone had a factory installed chain break that didnt involve oil loss prior to the incident.

Anyone? Thats what I thought.

My father purchased a genuine MB factory rebuilt OM615 engine for his 71 220D back in the late 70's - as I recall the wholesale price at the time was over 2K. He drove it for a couple of years then sold the car to me and I subsequently experienced a timing chain failure at around 120K miles.

The car had received regular oil changes during its service life and the failure of the chain was not caused by a vacuum pump issues.

I replaced the chain, cam and a couple of cam towers IIRC and the car remained in service for several more years before the body rusted away sometime in the late 80's.

edit:
Sorry I just got what you meant. You didn't mean that a part was leaking oil as an indication of the chain's impending failure. You were talking about the engine oil leaking out somehow, then later on the chain breaking due to lack of lube. Totally understand now.

Oil loss... I'm assuming you're saying that a timing chain should be predicted to break by an oil loss through something like the vacuum pump about to fail? If this is what you're saying, I think it's doubtful because it's the vacuum pump cam roller bearings that fail and fly into the chain. That wouldn't cause an oil loss at all.
or...
other people mentioned the guide rail tips flying off after wearing out into the timing chain. This is definitely a possibility but again, there wouldn't be oil loss.

At least I'm not following the oil loss idea that you're onto. Could you explain a little bit more of what your onto?



On another note, with things that could fail... is it even worth changing the chain without changing potential hazards to it (cam gear, rails, etc.)? And can the chain guide rails be changed with the 'Connect the old chain to the new one and feed it through under tension' method as in the haynes manual?

No on both. If you are going to replace the chain, you should replace the rails at the same time. Changing the rails isn't easy. I can post the FSM guides to changing the rails if you want.

Thanks Lance,
If you've got time to post that, I'd love to see it. I'll be changing my 603's chain and tensioner soon. It's probably a little different on a 617. May as well do the rest of the parts if I can. Isn't it impossible to get to the lower rails (with the engine in the car) on the 617??? seems like I read that somewhere, just wondering.
Nick

The 603 is much different, it has an actual removable timing cover while it's cast as part of the block on the 617.

That's what I thought on the 617. And I'm glad about on the 603! On my old 300d (84) I always wondered how the got those parts in there when the engine was manufactured! Doesn't look very service man friendly! I wonder how people like Metric Motors do it when they're rebuilding.

I replaced the tensioners in the engine in my 240D. I did it in the car. I had to remover the cam sprocket to get the one on the tensioner. The bottom two, I had to remover the vacum pump. On of the new bottom ones didn't fit, so I had to reuse the old one. I used new pins. I used a threaded bolt and nut to get them out. I would say the bottom two of mine were still good and probably the top one. The top one is easy to change. One guy told me if the chain gets sloppy, the flexing of it will take out the top one. The tensioner one had about 1/16 inch groves in it. My Odometer shows 250K, I think the car has nearer 300K on it. I had about 10 degree of chain streatch.
Tom

Forced, can u post other pics if u have them on the 617 chain, tyty

Sorry for digging up an old thread... My timing chain on my 1981 300TD with ~330k miles on it broke last week. This was the original factory chain. Car otherwise ran great. No oil consumption, no loss of oil in the incident.

I was accelerating lazily from a stop light when I felt a shaking in my right foot through the accelerator pedal and heard a clanking scraping noise and then the engine died.

The cam broke and it took out a couple towers.

My mechanic is recommending a motor transplant because it would cost about as much to get in and replace the cam and towers and chain. He's concerned that the teeth on the gears might be worn and that a replacement chain could be damaged and cause another failure.

Thoughts?

I'm thinking that my 6-year stint as a 123er is coming to a close. This car is in really nice shape. I'm amazed at the paint and chrome on these fabulous cars.

Part it out? Sell it as a project?

That might be me you're thinking of, but it was one chain break and one runaway that took the life of my motors.

The breakage on my w116 SD was at about about 8 years/100k miles following a rebuild (prior to my ownership). The stretch had been checked 18 months/12k miles previous and declared minor by a reputable shop. From memory (this was in 2001?) it took out the cam, at least one tower and bent some valves.

The runaway was on an old w126 that had serious issues to begin with and was mostly my fault anyway.

Do you think they rebuilt the Engine but reused the Old Vacuum Pump?

Or simply do you think the Vacuum Pump might have been the cause of the Timing Chain Failure?

Sorry to hear about your engine loss, know that sinking feeling especially when you are out in the middle of no where cruising along at 65mph.
every valve hit a piston, broke the two front cam towers, one off at the base and the other just under the bearing. cracked the valve cover, twisted the rearmost rocker and cracked the head.

If the body is in good shape, why not locate a used engine, maybe up grade to a Turbo 617.952. I see them in PNP from time to time, and not all are junk. pulled one with 97K.
some time I have seen them on Craigs List.

If you are done with the car and it`s in good shape, shame to part it out. the inventory on these is thinning down on good one`s.
really not all that difficult to R&R an engine.

Charlie

I know of one that broke a chain, only after is was replaced. The old style master link was used, the clip was facing in the wrong direction, flew off, and you know the rest.
Every chain that I have rolled on has received a crimped link, using the proper tool. Alan