Author Topic: Concensus on when to replace 6.9 timing chain rails?  (Read 204 times)

raueda1

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Concensus on when to replace 6.9 timing chain rails?
« on: 19 September 2019, 01:35 PM »
Some seem to insist on changing the rails whenever you replace the chain.  Others say that the design of the 6.9 tensioner and chain path doesn't stress or wear the rails so there's no reason to change them unless they're actually broken.  Perhaps this is another battle between the "replace on principal" crowd and the disciples of "if it ain't broke don't fix it."  I myself seem to vacillate from one to the other and then back again (usually governed by how hard the job is  ::) ).  Anyway, any thoughts would be welcome, as always.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

ptashek

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #1 on: 19 September 2019, 02:17 PM »
I'm with the "just do it" crowd on this one.
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rumb

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #2 on: 20 September 2019, 06:00 AM »
Yeah, just do it. It's a long way into there and you dont want to go back.  On my engine the main tensioner one was crumbling. There rest were fair, but well worth changing.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

daantjie

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #3 on: 20 September 2019, 07:15 AM »
+1.  The access alone with the motor out makes this a no brainer ;)
Daniel
1977 450 SEL 6.9 - Astralsilber

TJ 450

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #4 on: 29 September 2019, 05:30 AM »
This is how I go about it. If the chain is being replaced, the guides get replaced too. This is unless they are the lined alloy ones as on the 6.3 and other earlier models. The lower left guide one my 6.9 was one of these.

Obviously for the M116/7 it is mandatory to replace the guides.

With the chains, I have head it best not to use the master link with circlips and to use a peened one instead (requires a tool). I noted a lot of wear on the pins of the link fitted to my 6.9 when the heads were done recently and will need to modify this.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

raueda1

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #5 on: 29 September 2019, 08:56 AM »
This is how I go about it. If the chain is being replaced, the guides get replaced too. This is unless they are the lined alloy ones as on the 6.3 and other earlier models. The lower left guide one my 6.9 was one of these.

Obviously for the M116/7 it is mandatory to replace the guides.

With the chains, I have head it best not to use the master link with circlips and to use a peened one instead (requires a tool). I noted a lot of wear on the pins of the link fitted to my 6.9 when the heads were done recently and will need to modify this.

Tim
Hmmmm.    Very interesting.

re: rails -  Is this saying that the lined alloy guides are OK to leave alone unless there's an obvious problem?  In my case the only rail with notable wear is the curved one on the tensioner.  The rest look new - no grooves, no nothing.

re: chain - I just got a new chain from the Classic Center which included the master link.   I'd infer that they don't think it's too bad, or maybe they do it that way for user convenience (hah!).  Any idea how old your linked chain was?  Unfortunately I'm now being somewhat driven by expedience.  Got surgery in mid-Oct and what isn't done by then will likely sit until spring.  Thanks and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

UTn_boy

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #6 on: 29 September 2019, 11:34 PM »
This is how I go about it. If the chain is being replaced, the guides get replaced too. This is unless they are the lined alloy ones as on the 6.3 and other earlier models. The lower left guide one my 6.9 was one of these.

Obviously for the M116/7 it is mandatory to replace the guides.

With the chains, I have head it best not to use the master link with circlips and to use a peened one instead (requires a tool). I noted a lot of wear on the pins of the link fitted to my 6.9 when the heads were done recently and will need to modify this.

Tim

Back in the early 1980's there was a technical service bulletin issued stating that the master link with the circlips is safe to use provided the master link is installed in the correct orientation (citclips facing the rear, openings of the clips facing to the left side of the engine).  With the exception of the M-100 engines, every timing chain I've ever ordered from Mercedes comes with the circlip style master link. 
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1978 450sel 6.9 Euro, Anthr/velour

TJ 450

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #7 on: 01 October 2019, 06:59 AM »
Yes that’s my opinion on the alloy ones unless they are delaminating. The tensioner rail I think it is best replaced if available, they do wear significantly.

If you don’t replace them, I don’t think it is the end of the world as they don’t seem to get slapped by the chain as on other engines. The ratcheting tensioner would help this.

With the master link, I am running the circlip type but have been told by a notable MB mechanic that it is not advisable. The chain has been in my car roughly 10 years, 60,000km and it has notches worn in the pins of the link. It is a genuine chain and link. Admittedly this would also occur on the peened type but I found it concerning all the same.

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

UTn_boy

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Re: Concensus on when to replace 6.9 timing chain rails?
« Reply #8 on: 01 October 2019, 05:16 PM »
Well, always remember that experience doesn't always make any of us the wiser.  Tell your friend to look up the service bulletin if he doesn't believe you.  Like you, I've had the circlip style links in all of my cars for many years and hundreds of thousands of miles.  Never a problem.  And yes, if you take one of the other links apart you'll not the same wear.  The circlip style master link is made from the same material as the chain, and there are no stresses on the chain that would cause the clips to pop off.  It's perfectly safe.  Even Mercedes said so.  Granted, of the link is put on incorrectly it can come off. Maybe that is what your friend experienced?  Just guessing.  I really don't know. 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour