Checking chain stretch - is this correct? - PeachParts Mercedes-Benz Forum

Ceristimo · #1 04-17-2016, 11:09 PM

Sorry for opening all these topics guys. Thanks for helping me out doing my valve adjustment! Job completed successfully

Before putting on the valve cover, I figured I'd check my chain stretch. Aaand, I am reading about...0 degrees...

So, I lined up the markers on the cam-tower, to where the little opening in the ring is perfectly centered on the mark on the cam tower. It looks like it's not centered, but that's the angle of the photo, I had it perfectly centered (needed to rotate the engine 3 times through to get it perfect, I overshot it every time, fighting the compression)

I then read the stretch:

Soooo... Seeing how I have 280k miles on this thing, and the history of the car is unknown except for that the previous owner bought it from a W123 lover 4 years ago, and Betsie has had front suspension work done, a leather wrapped steering wheel and a dash pad and hood pad and other things that have been lovingly done to her:

Is there a chance this is not the original timing chain? Does this measurement mean that I don't have to worry about the timing chain at all for the next decade?....

Diesel911 · #2 04-17-2016, 11:36 PM

If the Bearing Tower Marks and the Cam Gear marks are lined up properly you are showing about 2.5 Degrees after TDC. Meaning your camshaft timeing is 2.5 degrees late.
However. 2 degrees of late timeing is normal after a certain amount of miles and there is no ofset key available to correct 2.5 degrees.

1 degree off at the Camshaft and bearing Tower equals 2 degrees off at the Cranshaft Damper. So the method you used gives you an aproximation.

However, if you want to be accurate you need to look up the 2mm method where you use a dial indicator and anther technique.

Ceristimo · #3 04-18-2016, 12:00 AM

Aah...Well, I had the marks on the camtower spot on...So, even though I'm pushing 280k, the chain seems to still be in reasonably good health then, and not something I have to immediately worry over?

Thanks for your comment, Diesel911.

leathermang · #4 04-19-2016, 12:18 PM

Quote:

Originally Posted by Ceristimo

Aah...Well, I had the marks on the camtower spot on...

The Factory Shop Manual specifically forbids using the marks on the cam for checking anything..... they will accidentally be right sometimes since the options are finite... but the FSM says not to count on them particularly for measuring anything and then making decisions based on those' measurements'....
it says those marks are only for putting the engine together at the factory and just so the cam will be in the ' correct quarter'....
Why don't you read the threads I keep in my signature ?
Do you have a copy of the FSM ?
I think you can access it on the web.... but a paper copy is really nice to have.... then you have to read it for it to do any good....lots of people on here have them but have not sat down and read them...

Clemson88 · #5 04-19-2016, 02:31 PM

280 miles ? Looks like you're about 80K overdue for a chain to me. I drove my SD about 10K without checking and changed it when I found the instructions here.

It's not that big a deal. I like clamping the chain to the cam gear with vice grips which have rubber hoses slid over their tips.

I covered everything with rags and ground the master link off the old chain. I also crimped a new link to join the old and new chains then ground it off to install another new link to finish the assembly.

The worst part is finding a chain crimping tool to borrow.

leathermang · #6 04-19-2016, 02:35 PM

The FSM warns that tension should be kept on the chain as the new one is rolled in... on the driver's side... so that it does not drop a sprocket on the IP.....many people wind up with the IP (18 ?) degrees off.... and wonder why it happened.....

Clemson88 · #7 04-19-2016, 02:43 PM

My short comment was in no way an comprehensive coverage of this activity. I just attempted to explain a couple of the things I did differently than some of the things I've read here.

I guess that's a disclaimer and next time I'll put it on my post.

leathermang · #8 04-19-2016, 02:54 PM

I am not attempting a thorough description either... I just try to post red flags in the FSM which almost never get posted on the forum. If I mention a red flag it is up to the OP or others reading later to check out if it applies to the situation.
People should not try to do serious work on their engines without reading the FSM.... then if they do not understand its instructions/warnings a forum can be of great help...

Ceristimo · #9 04-19-2016, 09:01 PM

Well, history on this car is unknown, except for the fact that the previous-previous owner put a lot of work into this thing. But that was 6-8 years ago. It then got sold to the guy I bought it from, who neglected it for two years, and I spend the last year chasing his neglect.

Point is: I wouldn't be surprised if this is no longer the original chain, but I'm not certain how one can tell, except for measuring correctly with the 2mm lift method. Guess I'll get a dial gauge...

leathermang · #10 04-19-2016, 09:09 PM

Quote:

Originally Posted by Ceristimo

Well, history on this car is unknown, except for the fact that the previous-previous owner put a lot of work into this thing. But that was 6-8 years ago. It then got sold to the guy I bought it from, who neglected it for two years, and I spend the last year chasing his neglect.

Point is: I wouldn't be surprised if this is no longer the original chain, but I'm not certain how one can tell, except for measuring correctly with the 2mm lift method. Guess I'll get a dial gauge...

The reason that is the most legit method... is that accumulated wear... which may not be additive... but the bottom line is what is measured...which is what counts... it is not that hard... just tedious... but due to importance... not too bad....

Diesel911 · #11 04-19-2016, 10:03 PM

If there was an offset Woodruff Key installed by the previous owner it would have corrected the old Chain.

leathermang · #12 04-19-2016, 10:10 PM

Quote:

Originally Posted by Diesel911

If there was an offset Woodruff Key installed by the previous owner it would have corrected the old Chain.

True and the FSM says that as long as those offset keys (several degrees are available ) bring the specs into compliance the chain is still good..

However, most of the time it is not the actual chain which causes big problems... but things which are in contact with the chain....so sometimes it is good to anticipate that potential catastrophic damage and change out the chain and those slides and rails to make sure that does not happen.

charmalu · #13 04-20-2016, 03:35 AM

Here is the Wiki on the 2mm lift method.

PeachPartsWiki: Measuring Timing Chain Stretch

Here is a good thread.

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

Charlie

Clemson88 · #14 04-20-2016, 10:36 AM

Just how far does this rabbit hole go? In post #4 on the "9 degrees of chain stretch," thread the cell gives a list of part that would require a lot more work than rolling a chain into the engine.

I've changed my chain and all of the guides which can be replaced without removing the timing cover. I did not change the cam sprocket Just how important is it to tear the entire front off a 617 to replace all this stuff. Yes, my 84 300 SD

I'm starting to feel like I've shown up for an eight-grade oral presentation buck nekkid.

leathermang · #15 04-20-2016, 01:29 PM

Quote:

Originally Posted by Clemson88

Just how far does this rabbit hole go? In post #4 on the "9 degrees of chain stretch," thread the cell gives a list of part that would require a lot more work than rolling a chain into the engine.

I've changed my chain and all of the guides which can be replaced without removing the timing cover. I did not change the cam sprocket Just how important is it to tear the entire front off a 617 to replace all this stuff. Yes, my 84 300 SD......

'Cell' did a great job on that explanation.... Your questions have to do with variables which are not usually findable.... did the prior owners use the correct oil, correct filter, and change those at proper intervals ? Usually what you did... roll in new chain and replace those things reachable without taking the front sheet metal off will keep the car going just fine... It is a judgement call having to do with things like the cost of a good replacement engine(assuming they are still available at that time in the future ) from the salvage yard or a parts car...which may or may not be easy to access AT the time in the future you need one...
In general ... if you have the space and the money and run across a good parts car... snap it up now... by definition they are getting harder to find and will continue that trend...