[alfa] What I learned about SS exhaust fasteners

["Jay Mackro" <jmackro@xxxxxxxxxxxx>]

In a recent digest, I mentioned that stainless steel bolts + nuts tended
to freeze up, especially when used on exhaust systems.  I received a
number of replies, and learned a great deal about this problem.  Thanks
to all who responded.

The concensus seems to be that you MUST use an anti-seize whenever
using SS hardware, even when it isn't exposed to heat.  One of the replies
that addressed the problem most directly advised:

    use zinc plated steel bolts, stainless steel split washers and brass nuts

which seems like the best approach.  While brass nuts won't take a lot
of torque (e.g., they're easy to strip if you over tighten on assembly),
these
joints don't require a lot of clamping force, and the anti-corrosion
properties
of brass probably outweigh its lack of strength.

The problem of exhaust system fasteners is an intersting one - you need
two properties:

  1) The joint shouldn't come loose under vibration in the early days - e.g.,
before everything rusts up solid.  I have had problems in this area when the
lock washer anneals from the heat, and the still unrusted nut & bolt just
vibrate loose.

  2) The joint shouldn't lock up due to corrosion, making it impossible to
take apart after it has been in place for a few years.  This is less of a
problem
where the joint is easily accessable - like on the catalytic converter -
since
it is easy to put a wrench on both the nut and bolt head, and if the fastener
fractures, so what?  But, corrosion can be a real issue when the fastener is
difficult to access - like where an early Alfa's cast iron manifold bolts to
the
downpipes.  There, it is difficult to apply enough torque to some of the
fasteners to just fracture them when they corrode.

I guess the tried and true method of using steel bolts and brass nuts is
probably the best solution.

Jay Mackro, San Juan Capistrano Ca.
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