Whooo. Sounds like a fun discussion here. I'll weigh in with my opinion (which is worth what you each are paying for it). Note that in this discussion, the engine type is VERY IMPORTANT. The criteria are drastically different for 61x and 60x. With that said:

For iron-head OM616 and OM617 engines:
The FSM says up to 10 degrees can be corrected with offset keys. The keys are available in 2, 4, 6, 7.5, and 10 degree increments. Does the chain need replacement? That is harder to tell than you'd think. I have heard of more than one fine-looking chain failing in a big way. For the 61x engine, my opinion is that it's not a bad idea to replace it on principle after ~250kmi, and maybe waaay sooner, if you intend to keep the car a long time. Another interesting factor is that the stretch (elongation, whatever!) does not necessarily return to zero with a new chain. This is, IMO, due to two things - first, the possibility of worn sprockets. Second, sloppier tolerances in the engine design. I believe the latter is why Mercedes allows correction with offset keys. I have a friend with a 617 who heard a funny noise, and discovered a chain link plate broke free and was cutting a groove through the timing cover! :eek: He rolled in a new chain. No offset key. Sprockets looked fine. We used my factory crimp tool on the new master link. When it was al done, the NEW chain showed SIX degrees off! Egads, it's worn, change it! :rolleyes: By Mercedes standards, his new chain can only stretch 4 degrees from new before it will require replacement, as it will exceed the 10 degree limit. Get the picture?


For aluminum-head OM601, OM602, and OM603 engines (and possibly 604/605/606 as well) :
The FSM is extremely explicit about these engines. When chain stretch (sic) reaches an indicated 4 degrees or more, replace the chain. There are no offset keys produced or allowed. A service bulletin (separate from the FSM) specified a more conservative limit of 3 degrees, instead of 4. My 603 chain showed 4 degrees stretch at 220kmi. When I rolled in a new chain, it returned the indicated stretch to ZERO, unlike the 617 engine. I believe this is due to tighter tolerances in the 60x engine design, hence the factory requiremnt for replacement, rather than adjustment.


The OM60x service bulletins are here:

http://www.meimann.com/docs/mercedes/OM60x_Timing_Chain_TSB.pdf

http://www.meimann.com/docs/mercedes/OM60x_Timing_Chain.pdf


Happy valve timing!

:D :D

difference after new chain?
 

Dave,

Any noticable difference in the performance after the new chain was put in?

Chuck

In my case, I have always changed the whole sprocket, tensioner as well as the guide along with my timing chain, no point in just changing the chain alone, the sprockets get equal amount of wear. The maximum life I have had out of a chain is 120,000Km. To me 3 degrees of stretch is enough to warrant a change.

leathermang,
The 81-85 300SD has a 617, OM617.951 to be exact. So do the '79-'80 SD's only it's .950 The TSB that I linked to was for 602,603,606 engines, but the procedure for checking the chain stretch on the earlier engines is the same. Line up the marks on the camshaft sprocket and camshaft bearing cap and read off the numbers on the crank damper pulley. Can it be any simpler?

The chains can and do break themselves when worn or defective, which is what caused Mercedes to issue the TSB in 11/95 due to reports of chain failure in some '92-'95 diesel engines. They found a small amount of defective chains had been installed at the factory (that self destruct) due to poor quality control, so they decided to replace any of the '92-'95 engines that chains wore to 3+ degrees under 50,000 miles.

To find out the condition of the chain,
Don't just look at it, don't take it off the engine and compare it with a new chain and don't guess. You should MEASURE IT

gsxr,
As to your friends engine, did you ever consider the pointer being possibly moved? It is a common source of error after replacing the chain, another being sprocket wear. I know the OM61x's were less advanced than the OM60x's but sloppy, come on! Was this the only OM617 you changed the timing chain on?

Certainly you can change the chain when ever you want on " principle" but if it's not worn (4 degrees OM60x or 5 degrees OM61x) there is no real reason to.


Chris

Sounds like Chris and I are on the same page. I do have the Om617 manual in printed form as well as microfiche. A law course I once took taught me two things. Read the whole article and don't take anything out of context. The OM617 manual says to check valve timing if there are complaints after valve work. The specs are 11.5 degrees with new chain and 13.5 with chain that has been in service over 20,000k. Service procedure 05-215 says that late timing can be adjusted with offset keys if elongated chain hasn't reached maximum specs. If passed specs, chain must be replaced. So I would assme that if Mb gave valve timing specs with a new chain and a chain that has been in service, those are the specs. As to the 10 degree key, the manual also states that the key can be reversed to subtract from an 18 degrees advance of the gear. Apparently MB is conservitive with two degrees, so I would have no problem with five degrees. Also MB has only three instructions for resurfacing a head. #1 resurface to specs. #2 check valve seat depth. #3 check valve timing per procedure 05-215.

Peter

I tend to follow a philosophy of, "if it's not broken don't fix it." Unfortunately for a timing chain this would be welcoming a catastrophe. I checked my timing chain for stretch a few thousand miles ago, I'm at a little over 226K on my 300D right now, and I had zero stretch. My car always had 3K mile oil changes, maybe that had something to do with it.

Chuck - there was a slight improvement in performance/noise/MPG but it may have been more placebo than anything. Not a huge difference. If your IP timing is off (due to the chain stretch) and that is corrected at the same time, you may notice a larger improvement. I got a measureable MPG increase with the IP timing set to the advanced side of spec.

Chris - on my 603, the pointer is perfect, because I set it with a dial gauge while the head was off! ;) The 603 pointer only adjusts over a 3 degree range total, btw. On the 617, I do not know for sure. However the 617 pointer is not something that looks like it would be moved, adjusted, or knocked accidentally (unlike the 603 where you can accidentally loosen the bolt while changing the water pump - don't ask how I know.) I also don't know the range of 617 pointer adjustment. HOWEVER, there have been others who rolled in a new chain and saw a significant amount of "stretch" with a new chain. Someone on this forum reported, IIRC, 4 degrees after rolling in a new chain, much to his dismay. I agree this is another possible source for error but don't have enough data to state the probability or magnitude. And I do agree that replacing the 60x chain before it reaches the limit is probably not necessary. I don't entirely agree with that on the 61x anymore after reading more than one anecdote of unprovoked chain failures that had not reached the 10 degree limit.

YMMV, etc...

:cool:

The gears (sprockets) and guides do not normally wear much on M-B diesels (if maintenance is kept up in accordance with the manual) and are usually not replaced until the engine is torn down and rebuilt(which shouldn't happen until 500+kmi with proper care), sure check them but it's rare for them to need replacing. The tensioner usually lasts longer then the chain(replacing it with the chain is a usual practice though). Timing chains can last anywhere from 250 to 500+kmi's depending on maintenance. OM60x's chains wear less then 61x's though the 61x's can tolerate more wear. Using synthetic oil is reported to cut chain wear in half or more among it's many other benefits.

gsxr,

10 degrees is NOT the wear limit for the OM61x engines, just the chain isn't likely to break until 7-10+ degrees. If and when stretch gets that high the chain needs to be replaced NOW not tomorrow! Recommended replacement is at around 5 degrees on the OM61x's. If putting on a new chain doesn't put the timing back at "0" and if nothing is found seriously worn, you can use a offset key to correct this. Some wouldn't bother if it was only off 3-4 degrees due to the fact that small changes in timing are not terribly critical on a diesel and usually anything between 0-3 degrees can be considered like new or unworn. This is the only situation where an offset key should be used.


Chris

Peter, GOOD! I see that YOU do have a 617 tubo manual.... as compared to Chris....

I take it that we are now past the " offset key is only for correction due to machining of the head " ?

Clearly the fact that they suggest checking elongation at a certain number of miles... means that they do not think there is going to be big movement of the head /head gasket or such.... so that what they are looking for is to keep tabs on CHAIN ELONGATION... right ?

"says to check valve timing if there are complaints after valve work" That is close.... but it says to check the valve timing using the position of the number one valve IF THERE ARE ANY PERFORMANCE COMPLAINTS..... not just after valve work.... one would certainly want to set everything to specs after something as major as valve works...but that is just part of getting the engine back into service....

NO it is NOT
 

Chris, "but the procedure for checking the chain stretch on the earlier engines is the same. Line up the marks on the camshaft sprocket and camshaft bearing cap and read off the numbers on the crank damper pulley. Can it be any simpler?"

No, the MB factory shop manual specifically requires using the position of the number one valve traveling a certain distance for checking ANY PERFORMANCE COMPLAINTS..... and such notables as Steve Brotherton, moderator and MB mechanic have settled this for most people in other threads....
And it was not too long ago that this happened....

Chris, ADMIT you have NO turbo 617 MB FACTORY SHOP MANUAL !!!
This will help others understand why you are avoiding logic and quoting the manual in your posts....

leathermang,

I am talking about checking the chain stretch on a used chain (which is what this thread was started about) NOT setting timing precisely on a new or nearly new chain(which is what the manual IS talking about). If you have a new chain and timing is still way off (and again if nothing is found worn) you can get out the dial gauge and offset keys to precisely check and correct it per the manuals instruction. It makes no sense on a used chain as when you will begin to notice performance changes the chain will need replacement(everything else being in order, pump timing ect.). Diesel engines are not as sensitive to valve timing being slightly (1-2 degrees) off like gasoline engines, where valve timing makes a BIG difference in performance.

Over the useful life of a diesel chain (about 5 degrees of stretch on the OM61x engines), there is little to be gained by using an offset key and beyond about 5 degrees of stretch the chain is worn beyond it's safe limit and should be replaced. I'm not saying that you or the manual is wrong or you shouldn't ever make it right, just that there are only certain times you need to be so precise. Production tolerances (not a problem on M-B diesels in nearly 30 years, was common on OM621 or 636 engines though) and when rebuilding an engine (to correct for the head being shaved and other factors) are the major reasons for using offset keys, NOT to correct timing error due to chain wear.

Chris

Chris, you should tell the folks in Stuttgart about your theory on the use of the offset keys. They have the reputation of taking things too seriously sometimes and as such could benefit from a good laugh too. I know I have!:D :D :D :D :D

I've read the sections in both books, offset keys can be used for BOTH procedures. The books state to replace the chain when stretch is "excessive" but does not define "excessive"...

Yes, it does define ' excessive'....it says replace the chain when the offset keys will no longer bring the engine back to specs...

Thanks Pete..... Chris does not have, and has not read the Factory shop manual for a 617 turbo engine.... thus we will have to cut him some slack.... but not more than 10 degrees measured at his crank..... LOL

Chris, We ARE talking about the same thing...
you are simply making up stuff which is directly contradicted by the instructions in the manual... both specific and implied.