[DML] Thread Galling

["content22207" <brobertson@xxxxxxxxxxxx>]

Just received an eMail Re: thread galling that shows there still is
misunderstanding about what it is:

Galling is NOT a problem that develops over time
Galling is NOT a result of different composition metals in contact
with one another
Galling is NOT affected by the outside environment
Galling is NOT limited to stainless steel (though stainless is most
susceptible)

Galling is basically welding. Occurs when self oxidizing metal
surfaces rub against one another too fast or too hard. Protective
outer layer is removed, heat is generated (friction or pressure), and
the virgin metal fuses. *ONLY* happens during fastening. If the
threads haven't galled at that point, they aren't ever going to!

Galling is usually a production line problem. Is difficult to do it in
your own driveway with a socket wrench (no cheater), especially if you
lubricate the threads first.

The eMail I received concerned stainless fasteners in an exhaust
system. That's one of the BEST places to use stainless. Single biggest
component of auto exhaust is water vapor! If you don't want to buy
Grady's new 7mm stainless studs (only place you'll ever find them
BTW), at least put stainless nuts on your carbon studs (Fastenal still
has 7mm stainless nuts). Other studs are common 10mm -- replace them too.

Or, you can snap the carbon studs off in the heads, drill them out,
replace them with new carbon, then repeat the process all over again
next time you replace exhaust gaskets...

Bill Robertson
#5939









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