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In correctly identifying a 3904351 block in terms of casting identifiers I am curious about the area next to the back of the block where the 3904351 is cast. In the area to the right of the block number most all block that I have seen have "GM2 HIPERF". I recently was looking at a 351 block that had "GM1" with nothing else and then on the far right side of the block was "HIPERF". Question is, is the "GM1 a real L71? And would it be judged correct?
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Re: Correct 67 351 Block - 435
Ron-----
The "GM1" and "GM2" denote pattern (mold) numbers. In PRODUCTION, several different patterns may be used since a lot of pieces have to be cast. As far as GM is concerned, all are the same and having the pattern number (and, certain other information) on the castings is used for quality control purposes.
Apparently, the patterns for the "GM1" and "GM2" patterns had the "HiPerf" embossment in different areas. This is quite common on castings from different patterns. The pattern makers at the foundry may do such things a bit different.
I an VERY confident that an L-71 engine could have been built from blocks cast from whatever patterns were used for the 3904351 block casting, be they "GM1", "GM2", or any other. The pattern number in no way relates to the final application of the block. The CASTING NUMBER (e.g. 3904351 or part number for the casting) is what's more relevent with respect to the final application of the block. However, even that's not the "final word". The "final word" as to application is found with the PART NUMBER for the FINISHED block assembly. Unforttunately, that number appears nowhere on the block, at all.In Appreciation of John Hinckley -
Re: Correct 67 351 Block - 435
The "GM1" and "GM2" are casting pattern numbers from which the molds were formed; they're just for traceability back to the pattern in the event of machining problems, and have no meaning in judging.Comment
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