Author Topic: 6.9 Tensioner leak, again...  (Read 98 times)

daantjie

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6.9 Tensioner leak, again...
« on: 05 October 2020, 10:31 AM »
For the 6.9 guys mainly...

This topic has been discussed before, if I recall as well on the old M100 board as well.

The 6.9 tensioner is somewhat unique in that you have to assemble it unit by unit onto the engine.  The flange is notorious for springing a leak, and after having gone through this about 4 years ago I am again seeing a slow leak from the tensioner, yay.

I recall some folks advocated for reducing the inner ring torque (40nm as per manual).  What is hella frustrating is that the (as usual sparse) instructions in the manual does not indicate a torque spec for the 2x mounting bolts on the head.  So most guys do this at 20nm.  The issue I think is that the inner ring pushes the flange away from the head @ 40nm, thus it overcomes the 20nm from the 2x mounting bolts :o I recall some folks saying to reduce the torque on the inner ring, but I do not know if this is wise, or by how much :-\

I added some Permatex Form - a  - gasket to the gasket the last time, and it seemed to have held it, albeit not permanently.

Any sage advice, I am not happy about effing around wth this again >:( >:( >:(
« Last Edit: 05 October 2020, 12:12 PM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

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Re: 6.9 Tensioner leak, again...
« Reply #1 on: 05 October 2020, 02:01 PM »
Torque is related more to bolt size, not directly to holding power.  Thus the different torques values dont affect the others holding ability. If you put 40nm on the small bolts you could likely break them.

When no torque value is given, then you can refer to a chart like this:
https://applifast.com/wp-content/uploads/2017/07/Applifast_Conversion_Table-Torque.pdf

I am not a fan of permatex, rather I would use black RTV instead.

'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

daantjie

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Re: 6.9 Tensioner leak, again...
« Reply #2 on: 05 October 2020, 02:15 PM »
Thanks Robert, I think the issue is more going into the aluminium head, I am worried that I will bugger up the threads if I go too high on the torque, which of course would be a whole new nightmare.  I guess I'll keep experimenting with sealants.  I tried Hylomar but it was a big flop, no good.
Daniel
1977 450 SEL 6.9 - Astralsilber

daantjie

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Re: 6.9 Tensioner leak, again...
« Reply #3 on: 05 October 2020, 06:51 PM »
Ugh this thing is giving me fits...

Fired her up and leak is even worse now.  Looks like the sealant might be making it worse???

I am worried that the flange and/or surface is warped so really up shit creek right now...
Daniel
1977 450 SEL 6.9 - Astralsilber