Hi Ted,
There is no "easy" and permanent solution. Retorquing is only a stop gap to
correct
something that is in the process of failing.
The BN1, BN2 head stud layout is not real good. You need to have everything
just right to
get a good permanent seal.
This includes having the head & block surfaces perfectly flat, using high
strength studs,
nuts, & hardened steel flat washers under the nuts & torquing to 75 lb/ft. Old
studs may
be stretched or just plain weak & will not maintain the needed clamping forces.
This will usually hold a three layer copper, composition, copper head gasket.
If the
compression ratio is raised considerably, a three layer steel gasket along with
the good
studs & flat surfaces, will usually hold. The surfaces need to be perfectly
flat to use
the steel gasket.
I think perhaps the most important is to have the head & block surfaces
perfectly flat
within 0.001 inch. The head's deck surface is already pretty thin & will not
tolerate much
milling. The original head is frequently found to be cracked even when it has
not been
milled.
The largest "out of flat" gaps are often in the areas between cylinders where
it is the
hardest to seal. I have an old head that has .008" gaps in the "between
cylinder" areas.
It won't hold, of course, with any gasket.
You can thoroughly clean the head & block sutfaces, lay a straight edge on the
surfaces, &
try to insert a feeler gage at various places along the straight edge. This
will easily
show any "low" spots where the head or block is not flat. When reassembling the
engine it
is good to lightly countersink the areas around the head stud holes in the
block. Any
"lifted" top threads will prevent the head from fully seating.
Denis Welch has very high quality studs, nuts, washers, & gaskets available but
they are
costly.
Regards,
Dave Russell
BN2
Ted Schroeder wrote:
> Subject: Blown head gasket
>
>
> About two years ago I had some head work done on my BN-1. I replaced the
>head using a
> new gasket. I coated the gasket on both sides with silver spray paint before
> installation. This fall the gasket blew between the rear two cylinders. Does
>anyone
> know what might have caused this? I can't remember if I re-torqued the head
>or
> not...probably not!
>
> I'd appreciate any advice as to what I should do to keep this from
>reoccurring.
>
> Thanks,
>
> Ted Schroeder
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