1967 327/300hp automatic convertible with PS and PB. Replaced the cylinder head covers a couple weeks past and jotted down some numbers. Looks like my cylinder heads are replacements, but am a little confused. The head had "3890462" stamped into it which makes sense for a 1967, BUT under that was "L275" over a "T". That seems to say, Tonawanda made Dec. 2, 1975. Does that make any sense? Were 3890462's still be made in '75? Also, saw "GM/5" and a time clock set to about 7:00. Any ideas? Thanks.
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Re: Cylinder Head Casting Date
Hi Kirk:
Attached is a photo of the casting number and date from one of the heads on my April 67 327/300 HP engine.
Others will have to clarify what your casting date means, but it might be December 27, 1965. The "T" does seem to imply Tonawanda.
I have read that one distinguishing feature of Tonawanda heads is that the "double hump" casting feature on the ends of the head has a rough, as-cast surface, while the Saginaw versions had a machined surface.
The "GM/5" is probably just a mold number, and the clock feature shows what hour of the shift the head was cast. The shift itself is encoded by the types of screw heads used on the date insert (two round, two flat, or one each).
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Re: Cylinder Head Casting Date
Kirk-----
I don't think that the GM casting #3890462 was still being manufactured in 1975. By that time, I believe that other castings had supplanted the '462' for SERVICE applications. However, if you're sure that the last digit is a "5", then it's unlikely that it represents 1965. I really doubt that the 3890462 had been released at that time. It's possible, I suppose, since it would be December, 1965, but if the date is actually 1965, then this head must be one of the very first 3890462 castings ever made. So, if it doesn't represent 1965, then it must represent 1975 and, perhaps, my notion that the 3890462 was out-of-production by then is wrong.
The interesting thing here is that if it was cast in 1965 at Tonawanda, the 1 digit year code was in common use at Tonawanda at that time. If it was cast in 1975 at Tonawanda, the 2 digit year code was in predominant use at that time. So, we get no help there in figuring this thing out.
Checking the double hump casting symbol on the head ends as Joe R described, would help confirm that these are Tonawanda castings, but the "T" virtually guarantees that.
Are both heads the same date and casting number?In Appreciation of John HinckleyComment
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Re: Cylinder Head Casting Date
Only got a chance to look at one while we were changing the covers. Could kick myself. I didn't really think anything about it, just wrote it down as I saw it. Are the double humps we'er talking about located on the "inside" and exactly where to check them. This makes me want to pull both covers and confirm, but I don't want to chip the paint since everything has just been redone. AHHH! I should learn to take pictures like everyone else.Comment
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'Humps' are on the outside ends... *NM*
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