Re: Turbo Exhaust manifolds

[raf40@oes.amdahl.com (Richard Funnell)]

>IMO the studs breaking is caused by the warpage of the manifold, not the
>differences in the coefficients of thermal expansion between the head and
>manifold.

This is what I was told when I had 3 studs break.  It seems reasonable
since the surface where the 2 dissimilar metals meet is nominally flat.  I
would expect most of the effect of different expansion coefficients would
be in shear.  Studs that size are extremely strong in shear, so I'd be
surprised if that would break them.  Warpage of the exhaust manifold, OTOH,
would cause severe tension on the studs, which is a much weaker direction.

Also note that when the problem occurs, the resulting noise diminishes as
the engine warms up and the manifold rejoins the head.

>My experience certainly supports the "get the manifold resur-
>faced and you won't have any further stud breakage problems" theory.  I had
>the manifold resurfaced >6 years ago and haven't had a problem since ...

All of you reporting no problems after resurfacing are making me feel
better, having had that done over 1 year ago.

>
>Steve Buchholz
>s_buchho@kla.com
>Department of Redundancy Department
>San Jose, CA (USA)

Richard Funnell,
San Jose, California
'83 urQ
'87 560 SL