Chris, I understand that you want to fill the existing grooves. As
such, you really want the "filler" to have the structural strength of
the parent material so as to provide an even crush (or surface loading)
over the entire head surface. You mentioned a "compound" to do that but
most of the stuff I know has LESS compressive strength than your
aluminum castings and a different thermal expansion ratio (CTE). I would
fill the o-rings with an aluminum wire. Ideally, the wire would be the
same alloy as your castings. Unfortunately, cast material is not
usually available in a drawn wire. I am assuming you heads are 356-T6 or
something similar. You might be able to find a wire in 2024 (an
aviation grade), 5083, etc. Unfortunately, I just moved all my reference
material and it is still boxed up. The key is to get a aluminum wire
with similar CTE properties of your head material. Now, I know you
DON'T want to completely TIG weld all over your heads. (especially if
they are T6 heat treated because they will loose their strength).
However, you could carefully get the wire a little larger than your
groove width and depth and you could carefully "peen" the wire in. If
done right, the idea is to complete fill the grove with good, strong
aluminum. Don't worry about leaving extra material above the head
surface. In fact that is what you want to do. Then a very light "kiss"
of a head surfacing sanding belt could do a good clean-up without
removing any head surface (or if careful, less than 0.001"). I would be
satisfied with that approach but you may want to be sure the "material
is firmly locked into the head o-ring. See message (2) to follow,
-Elon
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