Re: [ST] copper grease and torque settings

["Chris Harwood" <Chris@xxxxxxxxxxxxxxxxxx>]

At the risk of infuriating the rest of the list.....  it would be
interesting to know if the bolt rotated the same amount on successive
dry tightenings.

As a further variable in the real-life situation: I replaced the lower
wishbones on my GM Omega and they recommend new titanium bolts each time
(well, Haynes do, Vauxhall won't sell the w/s CDs to punters!).  So of
course I asked at the mfr spares counter where I bought the wshbones and
was told '..we don't stock them because we put the old ones back every
time"!

C'est la vie

Chris Harwood
00 RS

>>> frederic.nizery@xxxxxxxxxxxxxxxxx 25/06/2007 10:07:04 >>>
>...The nut was loosened then re-tightened to the proper torque. The
reading was
>now 
>lower. This was done two more times and each time the pressure was
less...


Problem is for something like piston rod head bolts, the type of
grease
to apply is specified and more and more it's a torque/angle procedure.
It's the case for the 955i engine.
But most of the cases, nothing is added to the torque spec.
That would probably mean it's for a brand new perfectly clean thread
and 
bolt .
Hence for some critical nuts, getting a new one each time is
specified.
The surface shape of the thread would probably change after the first 
fastening.

The result of the experiment you're describing is very interesting. I 
would have thought the opposite.
It tends to prove the the surface is damage at each tightening and the

friction factor gets higher.
It would probably change according to the surface coating (zinc, 
cadmium...) or not of the bolt.

Fred ST 02 BRG
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