Author Topic: Timing chain problem - after tensioner shenanigans!  (Read 163 times)

daantjie

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Timing chain problem - after tensioner shenanigans!
« on: 05 October 2020, 09:56 PM »
Hi guys

As is so often the case (with me at least), in trying to fix one problem, in this case a leak at the timing tensioner, I now have another problem...

I hope I did not ruin my motor, but here goes, I'll try to explain, might be long rambling :-\

At the last attempt (still leaking by the way), when I removed the tensioner I noticed that it came out with a lot of force, in that the tensioning rail was pushing it out quite firmly.  So when I tried to put the tensioner housing back in later on, it met with a lot of resistance, whereas before it would slip in easy, as the chain slack was on the tensioner side, so the rail would easily move back.

Now the rail is very stiff, and there is no slack on the "outboard" side, where I am standing, but the chain is very slack on the inboard side, HUH?

I am now  worried that I somehow jumped a tooth?  I made sure that the tensioner was clicking out as I pushed the spring in, and when I took it out it looked like before, with the inner pin approx 6-7 mm extended, thus to me it looked like it had taken up the slack as before.

Thinking back on how the motor ran on the last go round, it did start kind of rough, but smoothed out, and there was no chain slapping sound, it ran smooth, albeit as I recall quite rich I think, but maybe I was imagining that as it is always kind of rich at startup as I don't have any anti-smog crap on my car.


So, brain trust, what to do now???  I am tempted to "put the slack back" on the tensioning rail side by lifting the chain over the sprocket, but I think this is likely a dumb idea...I am just completety stumped as to how I "lost" the slack on the outboard side, did the rail somehow bind or bend?

Chain and tensioner is fairly new,  i would say approx 1k km since I did the job few years back and was running fine.

Any help appreciated as always 8)
« Last Edit: 06 October 2020, 07:38 AM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

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Re: Timing chain problem - after tensioner shenanigans!
« Reply #1 on: 06 October 2020, 07:37 AM »
If you are unsure if chain is on correctly best course is to remove both valve covers and line the cam and crank marks up.

You may have created slack on chain in certain portions just because the cams turn a small amount.  If you can turn the crank 2 revolutions it should take up all the slack in the chain. Or even just turn in backwards 1/4 turn and then back to where it was.

As far as leak goes, using new gasket? use a metal rule and check for any obvious out of flat situation. Make sure to clean mating surfaces with brake cleaner or such to remove any oils. Also tighten  1/4 torque value, let set about an hours or 2 and then tighten the rest of way. This should leave a bit more sealer on the surfaces.

I think I may have a spare tensioner if you want me to look for it.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

daantjie

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Re: Timing chain problem - after tensioner shenanigans!
« Reply #2 on: 06 October 2020, 07:50 AM »
Thanks Robert!  I still have my spare tensioner from when I did the job a few years back.

I am still really perplexed as to why this happened.  The tensioner was for sure "engaged" when I removed it the last time, the ratchet function seems to work fine, so even if there was an oil pressure issue, then surely the chain should still have been tight?  I really did not hear any metal sounds and the idle was very smooth from what I recall, so it all seemed perfect until I took the tensioner out the last time :-\

I guess I am going to have to get stuck in good and proper on this jobby now :'(
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Timing chain problem - after tensioner shenanigans!
« Reply #3 on: 06 October 2020, 09:28 AM »
If you are unsure if chain is on correctly best course is to remove both valve covers and line the cam and crank marks up.

You may have created slack on chain in certain portions just because the cams turn a small amount.  If you can turn the crank 2 revolutions it should take up all the slack in the chain. Or even just turn in backwards 1/4 turn and then back to where it was.

As far as leak goes, using new gasket? use a metal rule and check for any obvious out of flat situation. Make sure to clean mating surfaces with brake cleaner or such to remove any oils. Also tighten  1/4 torque value, let set about an hours or 2 and then tighten the rest of way. This should leave a bit more sealer on the surfaces.

I think I may have a spare tensioner if you want me to look for it.
Daniel, just PM'd you with more-or-less the same suggestion so I guess great minds think alike. ::)  I know your pain.  You try to fix X which upsets Y which in turn breaks Z.  Story of my life.

As I think about it I had some trouble reinstalling the tensioner too.  Somehow I was inserting the plunger too far so then tensioner body wouldn't go all the way in.  Sounds similar to your problem, maybe? 

As an aside, how do these tensioners actually fail?  Spring gets too weak or barrel wear leading to oil leakage past plunger and hence low pressure on the rail?  It's so simple it seems like there isn't actually much to go wrong.  Anyway, good luck......    Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: Timing chain problem - after tensioner shenanigans!
« Reply #4 on: 06 October 2020, 09:49 AM »
Thanks Dave!

What I have done on the tensioner install, all the times I have done it, same procedure:

- Slide assembled tensioner into head (pin not yet extended, thus the pin is more or less flush with the end of the body.  You could easily feel the slack on the chain lever/rail when pushing it into the head, it would easily pop in and out at this point
 - Mount flange
 - Install inner ring
 - Insert spring.  What I did here is to push the spring into the housing firmly, and then you can feel the pin ratcheting out somewhat, thus in the process it would take up the slack.  But I would think that just installing the closing plug, the spring would pop the pin out anyway.  I did this to ensure that the snap ring on the inner pin was properly engaged in the outer body.
 - Install closing plug
 - Fire up, no drama
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

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Re: Timing chain problem - after tensioner shenanigans!
« Reply #5 on: 06 October 2020, 03:09 PM »
OK some good news (I think) ::)

I was able to turn the motor by the crank for a few cycles, TDC marks line up, and no binding of the chain, so I would say so far so good?  You guys were bang on, the slack was mainly between the two sprockets, thus in the "valley", and pretty much immediately the slack returned to the tensioner area.

Still not sure how the heck this could have happened...The tensioner is supposedly a fail safe design, and I have to believe that it was doing it's job?

I have some parts inbound from the Classic Centre, will update this thread, hopefully with no KABOOM!

Cheers
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Timing chain problem - after tensioner shenanigans!
« Reply #6 on: 06 October 2020, 05:38 PM »
Sounds like GREAT news to me.  Solid work!
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: Timing chain problem - after tensioner shenanigans!
« Reply #7 on: 07 October 2020, 06:21 AM »
Depending on the cam position the strength of the valve springs can turn the cam a small amount. This would only happen when the tensioner is off.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550