1969 or 1979 block?

[Steve G.]

OK, first of I searched for an hour in the archives... close, but no cigar on this question!

I'm looking at a block that I thought was from a 1969. No numbers on the pad, never stamped, original broach marks. That makes me assume it's a service replacement. Not a warranty assembly, because its not a CE. Right so far?

Block number 3970010... commonly used from 69-79. Casting date is H 1 9... August 1 1969 or 1979. The "pattern number" above the block casting number is 20.

(Joe, I know you've addressed 3970010 blocks a zillion times on here, but you haven't touched on this subjects according to my search...)

No date around the starter area. Im getting told the 69 vs 79 casting dates looked different (really?) or that the pattern number would settle this (just dont have the experience on pattern numbers).

Any help?

[Michael W.]

Re: 1969 or 1979 block?

The shape of the stamp pad would be a good clue. Long and narrow would be '69, 'squarish' would be '79.

[Joe L.]

Re: 1969 or 1979 block?

OK, first of I searched for an hour in the archives... close, but no cigar on this question!

I'm looking at a block that I thought was from a 1969. No numbers on the pad, never stamped, original broach marks. That makes me assume it's a service replacement. Not a warranty assembly, because its not a CE. Right so far?

Block number 3970010... commonly used from 69-79. Casting date is H 1 9... August 1 1969 or 1979. The "pattern number" above the block casting number is 20.

(Joe, I know you've addressed 3970010 blocks a zillion times on here, but you haven't touched on this subjects according to my search...)

No date around the starter area. Im getting told the 69 vs 79 casting dates looked different (really?) or that the pattern number would settle this (just dont have the experience on pattern numbers).

Any help?

Steve----

IN GENERAL, I believe that the pattern numbers increased over time as patterns were replaced, added, or refurbished. I think this is especially true for a casting like the 3970010 that was in production for such a long period of time. For example, the pattern number on my original 1969 3970010 block, cast August 1969, is "17". The pattern number on a 1975 cast 3970010 block I have is "35". Just a coincidence? Possibly. However, I have observed many other examples of this GENERAL sort of progression of pattern numbers. So, on this basis I would say your block is a 1969-cast piece.

I have also been told, but never confirmed, that when a casting is in production for over a decade, the Saginaw practice was to use a 2 digit year date code for those produced more than 10 years after the initial use of the particular casting number. If so, a 1979 cast 3970010 would have a 79 as the last 2 characters of the casting date.

In this regard, it would be very interesting to hear from folks with 1979 Corvettes with 3970010 blocks and who could check their casting date. It would also be very interesting if they could check the pattern number, too. It's usually on the driver side of the block, near the casting number and right ahead of the "GM".

[Joe L.]

Re: 1969 or 1979 block?

The shape of the stamp pad would be a good clue. Long and narrow would be '69, 'squarish' would be '79.

Mike----


I was not aware that the configuration of the stamp pad ever changed on 3970010 blocks. However, it may have.

Could someone with a 1979 with 3970010 block check on this for us and, perhaps, post a photo?

[Harmon C.]

Re: 1969 or 1979 block?

Mike has the pad correct so this would be the easy way to tell. I think you are right Joe that a 79 block would have both the 7 and 9 for the year.

[Steve G.]

Re: 1969 or 1979 block?

Joe
I believe your observation makes sense that the pattern number was "higher" over time, although Ive heard some people say the '69ish pattern numbers were very low (3-10) but your number 17 is close to the 20 on this one.

I have that 1969 Corvette guide from Rick Bizzoco (sp?) and there is an engine photo which shows the pattern number 25, I believe. This doesnt assure that the photo is of a '69 motor, but you would think so.

The pad is the long and narrow earlier design.

The comment I heard today re: the size or spacing of the casting dates being different reportedly was from that "Chevy by the Numbers" book linked to the NCRS store by this page and incidentally, just ordered by moi.

[Jim T.]

Re: 1969 or 1979 block?

My 70 3970010 block cast D 25 0 has a 28.

[Steve G.]

Re: 1969 or 1979 block?

Helpful responses, thanks everyone. Sounds like a '69.

[Tom R.]

Re: 1969 or 1979 block?

Here's an L48 block from a 78...a late built

Engine Suffix VIN 31563 L48 4spd.jpg