Suspending cores in castings
In the 1970s, foundries suspended the inner cores that formed water jackets on what looked like safety wire. Since these wires extended out through the mold, these specific areas were reinforced with small round boss areas. You can see examples of 5 or 6 of these boss areas on the top of your cylinder head. When the alloy was poured into the mold, the safety wire became part of the alloy and essentially disappeared.
For whatever reason, in rare cases the suspension wire coming out through the very center of the back wall of the valve chamber would leave behind a tiny hole in the casting. In all the cases we've seen, maybe 4 or so in the last 30 years with about the same number being reported on the Forum, Universal drilled and tapped such a flaw to accommodate a 1/4" NPT flush pipe plug installed with a 1/4" Allen wrench. The quality of the rest of the casting was not adversely affected. The problem is that Universal used a plain steel pipe plug which corroded through at the end of the Allen wrench recess.
Last edited by Don Moyer; 09-26-2018 at 09:34 AM.
Reason: Typo
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