Timing Chain 617.952:
 

When is it recommended to replace the timing chain in the 617 motor?

Does it depend on chain stretch? Mileage?

Has anyone ever heard of or had one fail?

What other parts need to be replaced with the chain? Tensioner?

The reason I ask is that I have heard people say that if the chain dosent show excessive stretch then it isn't necessary to change it. I have also heard people exclaim that a car with over 280kmi should have it changed now! I have heard they rarely need to be replaced.

Looking for logic, reason and experience...

Thanks for your time,

Alec.

85 300TDT 280kmi

Ah yes, the ol' timing chain debate!

There are many different MB engines and timing chain arrangements. The 123 diesels are some of the best setups in this regard. As important as the chain(a double roller thank goodness), maybe even more important is the tensioner. Without tension on the chain, it will flop around and break a guide or something resulting in catastrophic failure. That said, the tensioner itself is simply a piston in a bore that holds hydraulic pressure generated by the oiling system. The good news is that this piston does not move rapidly inside the bore meaning that there is little or no wear.

There is a school of thought in which people feel that they must change the tensioner any time they change the chain, and who am I to argue in spite of the fact that I don't understand how it would wear out. In a high mileage engine with low oil pressure it is easy to understand that it might not hold the chain tight, particularly during start up before oil pressure is developed.

As far as when to change the chain, it's sort of like asking "how long is a rope?". An engine that has had religious, frequent oil changes, does not experience much particulate matter circulating with the oil. In that case the rollers and pins wear very little if any.

I think that IF the engine still holds very good oil pressure AND if the chain shows little stretch, you are okay.

To check stretch accurately, you need a dial indicator and the MB procedure to know exact valve lift specifications for accurate measurement.

You can get an idea of chain stretch by removing the valve cover and rotating the engine by hand using a 27MM socket on the crankshaft snout. Watch the mark on the number one cam bearing stand that is about 45 degrees from the top toward the drivers side. Once the camshaft mark perfectly aligns with the cam bearing stand mark, stop and look at the harmonic balancer timing mark. If the crankshaft is more than a degree or two past TDC, you might want to think about measuring it more accurately with a dial indicator, or changing the chain. If you change the chain, inspect the guides that you can see for damage or wear.

Good luck,

I see this mentioned a lot "To check stretch accurately, you need a dial indicator and the MB procedure to know exact valve lift specifications for accurate measurement. " Can someone give a brief description on how this is done. I have dial indicators but I can't imagine how this would be done.

Thanks.

Phil.

The dial indicator is used on one of the valves. Once the valve reaches the specified lift this is used to determine stretch. You need the factory procedure in order to have this specified lift measurement.

Have a great day,

hey folks,


Is there an upper limit where one should change the chain even though it still looks good and has a good history of oil changes. My 84 300d has 250K miles and I think that I am going to get it done anyway.

Any thoughts?

Thanks for all your replies.

bob

If you can turn the engine slowly with the valve cover off until the cam mark lines up, and the crankshaft is at TDC, you probably don't need to change it. This is not a 190E 2.3 engine with a single row chain. It is a double row chain.

If the engine has seen frequent, hot oil changes, the chain may very well have no stretch. You won't know until you check it.

Good luck,

Question, wouldn't adding a bypass oil filter help make the timing chain last longer? It filters out much smaller particles than the full flow filter and that seems to be the main cause for wear on the chain from what everyone is saying.

Either that or change it hot and change it often!

Have a great day,

Phil,

Steve gave a description on this subject. Check out the following link:

http://www.peachparts.com/shopforum/diesel-discussion/10414-help-i-need-check-stretch.html?highlight=617.95

David

Thanks, David. I did a search but must have missed that one.

Next time I have the valve cover off I'll be checking the stretch in a scientific way instead of the crude way. I estimated my chain to have about a 3 degree stretch using the cam alignment marks so I don't think I have anything to worry about. I believe I have the same engine as the one mentioned in that post so I'll check it using 2mm down on the intake valve and 11 deg ATDC. I hope these numbers are right...???

Phil