I think that using ARP lube is a good measure for all bolts that have
critical torque specifications. It lets you achieve an accurate torque
setting without having to worry about thread binding throwing off the
measurement. If it has no real value, it certainly can't hurt!
Joe (C)
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On
Behalf Of Jack W. Drews
Sent: Tuesday, March 16, 2004 7:36 AM
To: fot@autox.team.net
Subject: lube torqued fasteners?
I hate to get us off the track of fun discussions with a technical
question, but these can be fun, too.
Should we lube threaded fasteners on our 40 year old engines? If so,
what
torque readings should we use?
ARP, for example, says that moly lube should be applied to their
fasteners
to get accurate and consistent torque readings. And, when torquing
Carillo
rods with ARP fasteners, I adhere to their instructions to the letter.
But
that's a case where the folks at ARP designed the fastener and
determined
the torque values.
My question is in regard to fasteners and torque values that were
determined 40 years ago. My understanding is that at that time, all
torques
were specified "dry". This was true at the heavy equipment company where
I
worked until a few years ago, where exhaustive research was done on
fasteners and torque. Believe me, they torqued a bazillion fasteners on
their product and they were all done dry. Engineers knew that tightening
a
lubed fastener to the torques specified as dry would result in a higher
tension in the bolt. Furthermore, good practice on setting a torque
value
is to stress the bolt to 80% of its yield. At the same time, lubing a
fastener will cause an increase of 20 to 30% in the tension imparted to
the
fastener for the same torque reading, so lubing a fastener for which the
torque had been specified dry could easily cause the bolt to be
stretched
beyond yield.
Now the practical application of this in our engines can be thought of
in
terms of head studs and nuts. Stock head nut torque is specified as 90
ft
lb.. I believe that spec assumed a dry joint. If we lube the nut, we'll
put
20% more tension in the stud at that torque. And we all know that stock
head studs (not ARP) do stretch and the threads distort when
overtorqued.
Therefore -- what should we do -- torque dry or lubed?
uncle jack
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