Torque Values, What Fastener Lubrication does.

[Judy, Stephen, & Ian]

Most listed torque values in any tech manual (Bentley for example)
assume lubrication is used. Lubricating a bolt reduces the friction
between the bolt and nut threads. As a result, for a given torque a
higher bolting stress is realized in a lubricated vice un-lubricated
bolt. But what is more important by far when assembling gasketed joints
is that lubricating the fasteners results in more uniform results from
bolt to bolt, and so more uniform gasket sealing pressure. For this
reason you should always lubricate fasteners on gasketed joints.
There is also some difference in lubricants used. Any lubricant is
better than none. But the "slipperiest" lubricant ain't always the best.
The most important factor is how consistent are the results from bolt to
bolt. For example. If you lubricate 10 bolts with motor oil, 10 bolts
with nickel grease (anti-sieze), and 10 bolts with an advanced fastener
lubricant like Molykote P-37, the tension between the 10 oil lubricated
bolts will vary from one another much more than will the tension
between  the 10 nickel grease lubricated bolts which will vary from one
another more than will the tension on the Molykote lubricated bolts.
The other important consideration is long term corrosion resistance. for
this common nickel grease is very good.
So when in doubt; reach for the anti-sieze.
Steve Santoliquido
87 CGT