I've gotten so many helpful replies to my requests today I thought I'd
pass along an observation I made before my last road trip.
I've had trouble getting a good, persistent seal on my exhaust
manifold-to-downpipe flanges. The flanges are flat, and I've tried both
the copper- and steel-faced gaskets; neither lasts for long. The brass
stud nuts keep loosening, and I've gotten into the habit of tightening
them frequently. When going through the car prior to the trip, I was
tightening the nuts (again), and one of them stripped (moment of panic:
is it the nut, or the stud that's stripped???!!!). Anyway, I replaced
the nut with one of the many spares I keep and headed out on the trip
(3,600 miles in 9 days). Most days, I would lay on my back and tighten
the nuts with a ratchet, two extensions and a deep socket before
starting the day's driving.
What I noticed: the nut that was replaced stayed tight, while the other
5 were always various degrees of loose at the start of the day. I
surmised that the threads on the soft brass nuts either erode or
distort, making it impossible to keep good torque/stretch on the studs.
It could be that brass nuts should not be re-used--the
new-when-installed, never tightened brass nuts on my head-to-exhaust
manifold studs have been fine for many miles--but I've never heard that
anywhere.
My recommendation is to not re-use brass nuts on exhaust studs, they
aren't cheap nor are they particularly expensive, but they don't seem to
be reusable. Alternatively, you could use steel nuts with anti-seize,
but I don't know if this is a good idea (anyone?).
bs
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Bob Spidell San Jose, CA bspidell@comcast.net
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