Need help with casting number

[Dennis H.]

I am looking at a 67 roadster with a replacement block. The owner says it was a replacement engine supplied by the dealership in 1970. The casting # is 3959512. I cannot find this number in any books that I have. I checked it myself. It is very clear. Does anyone have any info? Thanks in advance.

[Lynn H.]

Re: Need help with casting number

Dennis,
I have one of these blocks myself, and I have it in one of my books. The book I have it in says for the years 62-63. What is the casting date? I was told awhile back while investigating the block that I have that it was a service replacement only, never used in production.
Lynn

Books says-327 CI, 250 HP, 2 bolt

[William C.]

Re: Need help with casting number

Mortec says 62-67 2 bolt service block. Casting date likely 68-71?

[Dennis H.]

Re: Need help with casting number

Lynn thanks for the reply. The owner told me that. He said it was a replacement and that was why it was not in the books. I didn't say anything but I thought that did not sound right. I could not imagine GM casting a special block for repalcement only, but maybe they did. I hope someone else enlightens us.

[Dennis H.]

Re: Need help with casting number

Thanks for the quick replies. I should have checked the archives first. After checking there, I see that the 512 small block casting is not too unusual.

[Joe L.]

Re: Need help with casting number

Lynn thanks for the reply. The owner told me that. He said it was a replacement and that was why it was not in the books. I didn't say anything but I thought that did not sound right. I could not imagine GM casting a special block for repalcement only, but maybe they did. I hope someone else enlightens us.

Dennis-----


I've always thought that it was unusual, too, that this casting number was used for SERVICE only. However, keep in mind that this is a small journal, 4" bore block. The part number indicates that it was a late 1968 or early 1969 released block. By that time small journal blocks were not used for any PRODUCTION application. So, it pretty much had to be a SERVICE only piece.

Also, I've never seen one of these blocks in any confirmed PRODUCTION application. In every instance I'm aware of, the block was obviously a SERVICE piece.

[Cecil L.]

Re: Need help with casting number

CE replacement service blocks:
3959512 small journal 327 pass/truck
3959532 283 pass/truck
3959534 283 Chevy II
3959538 small journal 327 Chevy II

[Lynn H.]

Re: Need help with casting number

Dennis-----


I've always thought that it was unusual, too, that this casting number was used for SERVICE only. However, keep in mind that this is a small journal, 4" bore block. The part number indicates that it was a late 1968 or early 1969 released block. By that time small journal blocks were not used for any PRODUCTION application. So, it pretty much had to be a SERVICE only piece.

Also, I've never seen one of these blocks in any confirmed PRODUCTION application. In every instance I'm aware of, the block was obviously a SERVICE piece.

The block that I have is dated B21 4, I had assumed this was 64, due to the fact that the book I have that lists this block states 62/63. If the part number is indicative of the 68/69 release, then maybe it is 74??
Lynn

[Joe L.]

Re: Need help with casting number

The block that I have is dated B21 4, I had assumed this was 64, due to the fact that the book I have that lists this block states 62/63. If the part number is indicative of the 68/69 release, then maybe it is 74??
Lynn

Lynn------


It has to be 1974. There's no way this block was around in 1964. By 1984, it was long-gone.

[Lynn H.]

Re: Need help with casting number

Lynn------


It has to be 1974. There's no way this block was around in 1964. By 1984, it was long-gone.

Thanks Joe!! Always good to have an idea of what I have. I am not sure why I am even keeping this one around, except for the fact that it is in excellent condition. I figure someone I run across may have a use for this "small journal" 327 block someday. As always, your posts and information is very much appreciated.
All the best in the coming year,
Lynn

[Joe L.]

Re: Need help with casting number

Dennis and Lynn-------


Another thread made me think of something in regard to the 3959512 block. Is this block designed for the use of a canister-style oil filter or a spin-on type? In other words, does a canister-style adapter (GM #5573979) or a spin-on style adapter (GM #3952301) bolt up directly to the block?

[Lynn H.]

Re: Need help with casting number

Dennis and Lynn-------


Another thread made me think of something in regard to the 3959512 block. Is this block designed for the use of a canister-style oil filter or a spin-on type? In other words, does a canister-style adapter (GM #5573979) or a spin-on style adapter (GM #3952301) bolt up directly to the block?

Joe,
I did not think of this earlier, as it certainly would have made a difference in "dating" the particular block that I have. I did just have a look at it, and it IS NOT machined to accept the cannister/cartridge type of filter, it looks like intended for the spin-on type filter. I would say this is confirmation of your assessment of the date of my block being 74 and definitely NOT 64.
Lynn

[Joe L.]

Re: Need help with casting number

Joe,
I did not think of this earlier, as it certainly would have made a difference in "dating" the particular block that I have. I did just have a look at it, and it IS NOT machined to accept the cannister/cartridge type of filter, it looks like intended for the spin-on type filter. I would say this is confirmation of your assessment of the date of my block being 74 and definitely NOT 64.
Lynn

Lynn------


Yes, it does further confirm the 1974 casting date although, given the casting number, I don't think any further confirmation is really necessary. However, the issue I was really trying to get at was this: I never could figure out why the casting number for these small journal blocks changed about 1968 or 1969. Now we know the reason.

Here's what I suspect occurred: in 1968 when the the change was made to the spin-on filter for all PRODUCTION applications, a change was necessary for not only the blocks but also for the tooling used to machine the blocks at Flint. If the small journal, canister style blocks were to be continued to be produced for SERVICE, then there would have to be different tooling (i.e. the pre-1968) used at Flint to manufacture the SERVICE blocks. That would be expensive and create a "manufacturing complexity" that GM did not want to be created. I realize, of course, that there had to be different tooling to machine the small journal features of the block but there was no way around that. There was a way around having to differently machine the oil filter provisions and that was to create block castings which all used spin-on filter configuration.

So, a new series of castings was created so that all blocks would use the spin-on filters. In all liklihood, the blocks used mostly existing patterns modified for the spin-on filter. Of course, the change did require a change in casting numbers.

The above is further supported by the fact that although many trucks, taxi cabs, and police cars continued to use the canister style filter after 1967, they did not use a canister style block. They used a spin-on style block with a special oil filter adapter.

I don't know if Tonawanda small blocks were the same as above. However, it may be that Tonawanda manufactured no SERVICE small blocks for small journal applications after 1967. Likely, all SERVICE small blocks and engines were consolidated at Flint if Flint was not always the source for SERVICE small blocks.

For big blocks no corollary change was necessary. The only significant change to the blocks for 1968 was the change to the oil filter. Due to the much lower volume, Tonawanda likely manufactured a small inventory of canister style blocks for SERVICE and when these were gone, the spin-on style blocks replaced them for SERVICE of pre-1968 applications. If one wanted to use a canister style filter with these blocks, simply use the special adapter (99.99% of the folks at the time wouldn't have cared about the difference in the configuration of the blocks relative to "originality").

[Lynn H.]

Re: Need help with casting number

Lynn------


Yes, it does further confirm the 1974 casting date although, given the casting number, I don't think any further confirmation is really necessary. However, the issue I was really trying to get at was this: I never could figure out why the casting number for these small journal blocks changed about 1968 or 1969. Now we know the reason.

Here's what I suspect occurred: in 1968 when the the change was made to the spin-on filter for all PRODUCTION applications, a change was necessary for not only the blocks but also for the tooling used to machine the blocks at Flint. If the small journal, canister style blocks were to be continued to be produced for SERVICE, then there would have to be different tooling (i.e. the pre-1968) used at Flint to manufacture the SERVICE blocks. That would be expensive and create a "manufacturing complexity" that GM did not want to be created. I realize, of course, that there had to be different tooling to machine the small journal features of the block but there was no way around that. There was a way around having to differently machine the oil filter provisions and that was to create block castings which all used spin-on filter configuration.

So, a new series of castings was created so that all blocks would use the spin-on filters. In all liklihood, the blocks used mostly existing patterns modified for the spin-on filter. Of course, the change did require a change in casting numbers.

The above is further supported by the fact that although many trucks, taxi cabs, and police cars continued to use the canister style filter after 1967, they did not use a canister style block. They used a spin-on style block with a special oil filter adapter.

I don't know if Tonawanda small blocks were the same as above. However, it may be that Tonawanda manufactured no SERVICE small blocks for small journal applications after 1967. Likely, all SERVICE small blocks and engines were consolidated at Flint if Flint was not always the source for SERVICE small blocks.

For big blocks no corollary change was necessary. The only significant change to the blocks for 1968 was the change to the oil filter. Due to the much lower volume, Tonawanda likely manufactured a small inventory of canister style blocks for SERVICE and when these were gone, the spin-on style blocks replaced them for SERVICE of pre-1968 applications. If one wanted to use a canister style filter with these blocks, simply use the special adapter (99.99% of the folks at the time wouldn't have cared about the difference in the configuration of the blocks relative to "originality").

Joe,
As usual I would bet your "suspicions" to be fairly accurate if not exactly on the money. I never really put much thought into the "whys", as without someone of your caliber to help me think through the process, I usually cannot come up with conclusions that I can convince myself with.
As always, THANKS!!
Lynn