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Post Info TOPIC: '85 Timing Chain or Camshafts First


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'85 Timing Chain or Camshafts First

Hi Folks,

New to the forum but have been browsing for sometime.

I recently inherited the responsibility of two W126's. I have all the parts to do the timing chain but when I took off the valve covers, I saw that two camshaft lobes on both sides looked and felt compromised enough to change out both camshafts.

What should I do first, timing chain or camshafts? I would appreciate the professional outlook on this since I have never worked on MB vehicles. I've done extensive work on other vehicles though.

I am still looking for some camshafts as well.

Much Appreciated !!


1985 500 SEL

1991 560 SEL


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If you have two worn down lobes on the camshaft you should replace them at the same time as the chain as these cylinders are not going to be operating the same as the rest and eventually it will become a noise and drive-ability issue.

Mercedes vehicles are very difficult to work on, many will not even touch them. The ironic thing is, once you get to understand how a Mercedes is built they become much easier to work on. Unlike many other manufactures I see Mercedes routinely use special tools to make for a quick and easy repair, but these tools can be costly! More so when a Mercedes is in the first 10-15 years of service.

These are not roller follower engines, so it will be normal to have some small scratching on the lobes and follower as the vehicle ages but it should be proportional across all the lobes. You should also check the plastic oil rail retaining clips on the cam towers to ensure that none are broken or plugged. You will also want to replace these when you do the cams and chain.

Good luck.


What is to give light must endure burning -- Viktor Frankl


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To do the job, including new camshafts, these are the major steps....

* Drain your oil, & replace with new filter assembly.
* Remove rocker covers, along with whatever else is needed to do the job, including all drive belts & necessary auxilliaries.
* Rotate the engine via the 27mm hex-bolt as fitted to the crankshaft, & bring to TDC, no.1 cylinder.
* Remove the cam-followers for each cylinder, using OEM tool or similar, whilst following the firing-order-sequence.
* If replacing with new camshafts, you'll need new cam-followers too.
* Bring the engine back to TDC, No.1 cylinder.
* Take note of the marks visually on the camshafts, for reference points of correct timing. Look at the cam-towers & camshafts at forward engine for these marks.
* Once satisfied that the timing is correct, remove the cam-chain-tensioner.
* Use a 22mm spanner to hold camshaft in position, & undo camshaft fastening bolt. ( There's a cut-out for the spanner behind the sprocket ).
* Secure the cam-chain with wire or similar, to prevent it falling into the sump.
* Remove the camshafts, & fit the new ones, ensuring that the lobes are coated well with a moly-lube-paste. Oil the bearing journals.
* Refit the cam-sprockets & chain. ( Loosely fit the tensioner too if you want )
* Install the new cam followers, following the firing order once again.
* It's well worth changing the chain-guides too whilst you are here. See the w126 section here on this forum for pics. An M117 engine was pictured. Use this thread to learn about replacing the cam-chain.
* Replace the oil-lube-tube plastic clips. ( Clean out the tubes with de-greaser or similar before refitting ).
* Double check your timing marks align as they should.
* Refit rocker-covers & remaining items. Check oil level.
* Start-her-up, & maintain 2000-rpm for about 15-minutes to aid in mating the new cam & followers.
* Check for leaks & low fluid levels. Correct & drive away !



-- Edited by Rastus on Friday 9th of November 2018 08:22:32 PM

-- Edited by Rastus on Friday 9th of November 2018 08:24:20 PM


"Only an alert & knowledgeable citizenry can compel the proper meshing of the huge industrial & military machinery of defense with our peaceful methods & goals, so that security & liberty may prosper together". Dwight D.Eisenhower.


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Gentlemen, thank you so much for your responses!!

I have been educating myself since February this year and have learned something new from you both - thanks!

Thanks so much for the good luck and the major steps.

In preparing for the chain replacement, I did purchase the chain,
all the guides that I can get to from the top with new pins (just in case),
a puller for guide pins since I didn't know about the valve cover bolt trick to extract,
two master links - one set for following and the other to remain with the chain after rolling,
chain tensioner gasket - hoping the tensioner itself is good,
oiler kit - for cam towers,
two cam sprockets,
valve cover gaskets,

I just got the valve spring compression tool after realizing I would need to do the cams.

What size hex key socket do I use for the cam tower bolts and how do I get to the bottom tower bolt on cylinder number 4 back (firewall) right?
Do I need to do the torque sequence in reverse and what is the sequence?
At what step would it be best to replace the cam gear/sprockets?
Is it okay to use an impact gun on the cam bolts?
Whether I use new or used cams is it necessary to change cam bearings?
I have found some used cams with the towers and followers as a matched set...
Do I need new tower bolts?
Right now my right cam looks to be off about two degrees or so with the crank timing mark at 0, left cam lined up and distributor rotor on mark (#1) - I assume to chain stretch
Are the compensators "rebuildable" - can I take them apart to clean and pump up again? Can I still test them? Its been sitting since Feb.
I really appreciate the sequence. I couldn't figure that out.
So, cams, then maybe sprockets (how best to make sure they go on the chain the right way?), then chain, then happy ending.

Oh, what weight and type of oil and filter do you recommend? only 154k miles.

Much appreciated !!



1985 500 SEL

1991 560 SEL


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Posts: 16038

You run a very real risk of stripping out the threads in the engine block every time you crack loose a cam tower bolt.. they are extremely tight and one of them is at an angle to improve strength. If you strip even one bolt it is really-really bad news.


IIRC the cam tower bolts are either six or eight Allen, I will have my valve covers off tonight and be able to refresh my memory.

The torque specs and the sequence I do not have on hand but I do have them in my W126 book. If you are unable to find them elsewhere let me know.

Depending where you are located you could run either a 10w30 for colder climates or a 10w40 if you live in a hot climate.

Compensators may be rebuildable but I have not seen anything in the ways of kits or instructions.

I may have missed some of your questions but I got to run, heater is running.


What is to give light must endure burning -- Viktor Frankl

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