Quote:
Originally Posted by fastd
curious: mine say "Halibrand" inside the ear on the front. on the back there are 3 castings: "Alcoa" on one ear, "H326A" on the next and "6061" on the last. do these casting given an indication of vintage or anything else interesting?
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H326A was Ted Halibrand's number for the raw forgings. Raw forgings could be machined and otherwise processed to suit several different types of cars. 6061 is the aluminum alloy and the number without a suffix doesn't describe any stress relieving, aging, or hardening treatments Halibrand put finished parts through.
Blanks (raw unmachined forgings) made before mid summer 1968 (all the originals from SA) were forged by the Harvey Aluminum company and had Harvey's logo on the reverse of one wing. ALCOA bought Harvey Aluminum in mid summer 1968. When ALCOA started forging blanks for Halibrand Engineering the new blanks had ALCOA on them making differentiating Cobra period parts from later parts real easy.
Sometime around maybe 1969 or later a new set of forging dies were made and they of course were marked ALCOA. If you put early and late versions of ALCOA marked parts side by side you can see differences due to different tooling.