X-Mozilla-Keys:                                                                                 
Bill Freeman wrote:

Paul,

I don't have a feel for how serious a problem the thru-bolt
crushing of the aluminum housings really is.  If this is a serious
problem, I would suggest that I can take a look at the overall
problem and see what the possibilities are.  VW ran into a
similar problem in the late 60's/early 70s when they increased the
bore size and raised cyl head temps due to the leaner mixtures
associated with emissions control.  Their cyl head studs would
pull out of the magnesium crankcase.  The first fix (by repair
shops, not VW) was to install "case inserts" which were 12mm
outside thread/10mm inside thread steel pieces, and retaining
the original 10mm studs. Later on, VW
retained the std 10mm case threads but put in 10mmOD/8mm ID
steel inserts and used 8mm diameter studs.  The smaller diameter
studs had a lower spring rate and limited the peak loads on the
stud/case interface threads (which were still 10mm, like the original
studs) and the problem was solved.

My guess is that if this is a serious enough problem, that it may be
possible to either turn down the original studs/bolts (which are they?)
over most of their length (middle) and keep the peak compressive stresses
on the aluminum housings low enough to avoid crunching them.  It may
cause high enough stresses to yield the bolts (due to increasing the
stress by reducing the area) so we may need to go to a higher
strength alloy and/or heat treat.  Would be nice if turning down
the original bolts/studs would work, tho.

Is this worth the effort, or is this a non-problem in most cases?

Bill

I think it is worth it Bill. I have a housing that I can cut
up and send you the pieces if you want to expieriment a bit.
Perhaps Bruce can scare up an early necked down and late
not-necked down tension bolts. Also I will pop for an ARP 
necked down bolt for R&D purposes.

I am out of spare time and Robin is dragging me off to Europe
next week to visit friends and go to the Frankfurt auto show.

Paul Lamar
 
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