Hi Gary,
My experience with this comes from building race cars and high performance
engines.
When a $1.00 bolt failure costs 1/5th of a years income, a person learns
what not to do.
> reassemble everything. I've followed the thread about using lock-tite.
> However, the manual says to use grease and so does the local machine
shop.
> Anything wrong with using plain old grease on the threads?
I use "grease" on wheel lug nuts, and oil on connecting rod threads, but in
those
applications the bolt and nut is actually distorted by the tension applied
when the bolt is torqued. It is the distortion of the hardware that "locks"
the bolts firmly in place without threadlocking materials or devices.
If you aren't tightening the bolt enough to stretch the bolt and distort
the threads, grease or oil is generally a poor idea. Grease is generally a
bad idea
anyway, because the viscosity is too high and the threads "float" on the
grease when torqued lightly. It's OK if the application is low stress, but
not if the bolt is worked anywhere more than a few percent of it's rating.
I'm virtually 100% positive grease is a bad idea in this case. Even if the
rotor and bolt are high enough quality to allow you to stretch the bolt
enough to "lock it" in place without a failure, the rotor plate is probably
not hard enough. If the "soft" plate compresses even a few thousandths of
an inch, you'll loose all the bolt locking when the bolt shaft is short in
length and not stretched more than the wear amount of the plate.
I'd use good bolts and a soft-grade threadlocking compound and torque a
safe amount for the rotor threads. The compound will protect and lubricate
the threads when you install the bolts, and prevent them from falling out
even if the rotor plate compresses or wears at the holes. Since the bolts
are mostly in shear, and not in stretch or compression, the main problem
should be "falling out" and not hardware failure.
A large OD, thick, and *hardened* washer that PROPERLY fits the bolt shaft
would be a big help, because it would spread the load on the rotor plate.
The weak point then would surely be the rotor case threads.
Remember, either you lock the bolt with something or you stretch it more
than the amount everything else changes. If you don't, it will eventually
get loose. Grease or oil is only a good idea when the bolt is stretched by
installation torque more than the amount of give in the other materials.
73 Tom
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