block casting number size

[Tim Sargent]

I have noticed the same casting numbers are different sizes on Chevy blocks. In particular I have two 327 cylinder blocks with the casting numbers 3782870, one has the large numbers the other smaller. Both have 1965 casting dates patterned MMDDY the one with the larger number is a very late model year June casting. Both have Flint (V) stampings on the engine pad. Is there any understanding as to why the same casting number molds were different sizes?
Are the larger casting numbers on all later 65 production cars? Is either correct for Corvettes?
Thank you

[Joe L.]

Re: block casting number size

Tim-------

As I recall, 1965 MAY have been the year that some Tonawanda-cast small blocks were used for a small number of Corvette (and, probably other) engines machined and assembled at Flint. So, I would check the blocks to see if there is any indication that one or the other was Tonawanda cast. That MIGHT explain the difference in numeral size. A Tonawanda cast piece will usually have a more-or-less large "T" cast one or more places on the block. So, you might look for that. The single digit year code does not always indicate a Saginaw cast piece; some Tonawanda cast pieces used single digit, too. You can also check the area above the timing cover on the block. I believe that Tonawanda cast blocks have no pipe plug installed and Saginaw-cast blocks do have the 1/8 NPT pipe plug toward the passenger side of the block.

Aside from the above possibility, I would say that the different numeral sizes are just a function of the different patterns that were used to cast the blocks. For one reason or another, when one pattern was made a certain size was used and when another pattern was made, a different size was used.

I think that Mark Gorney would be the best source of an answer to this question; I hope he's around.