DZ 302 186 heads

[Flowjoe]

... Also, Saginaw/Flint blocks had a 1/8" NPT square-head plug in the front of the block, just above about 11 o'clock on the timing cover; Tonawanda blocks didn't have the hole or the plug. Photo below.

any reason why?  Wouldn't corporate GM use one mold design across all corporate entities for standardization?

[melav8r]

Definitely. The year portion of the casting date code on a Tonawanda block is two digits, and it's only one digit on a Saginaw casting (like C 3 9 on a Saginaw block, which would be C 3 69 on a Tonawanda block. Also, Saginaw/Flint blocks had a 1/8" NPT square-head plug in the front of the block, just above about 11 o'clock on the timing cover; Tonawanda blocks didn't have the hole or the plug...

Does that apply to Small Blocks, specifically trying to identify any differences between a Tonawanda cast small block and a Flint Casting.

[JohnZ]

any reason why?  Wouldn't corporate GM use one mold design across all corporate entities for standardization?

The block machining process differed slightly between Flint and Tonawanda; although both sets of tooling were installed in 1954, Flint modified theirs for what they considered to be a more reliable method of creating an intersection in the front oil gallery by gun-drilling that hole from the outside and then plugging it. Tonawanda elected to stay with the base design and create the intersection from the inside; this difference remained all the way through the production run of the Gen I block.

If you find a block with a single digit for the year in the casting date and the plug in the front, it's a Flint block; if the year is two digits and there's no plug, it's a Tonawanda block.

[melav8r]

JohnZ, What about a '68-'69 SBC with a single digit for the year, possibly no front plug, but stamped with a Tonawanda assembly-date/engine-i.d. stamp? Until I confirm the front plug, is there a possibility Flint blocks were shipped to and assembled in Tonawanda?

[KurtS]

Both plants had dedicated foundries nearby, so generally no blocks were exchanged between them. But exceptions could occur.

Post or email me a pic of the pad and I'll take a look.

[Flowjoe]

any reason why?  Wouldn't corporate GM use one mold design across all corporate entities for standardization?

The block machining process differed slightly between Flint and Tonawanda; although both sets of tooling were installed in 1954, Flint modified theirs for what they considered to be a more reliable method of creating an intersection in the front oil gallery by gun-drilling that hole from the outside and then plugging it. Tonawanda elected to stay with the base design and create the intersection from the inside; this difference remained all the way through the production run of the Gen I block.

If you find a block with a single digit for the year in the casting date and the plug in the front, it's a Flint block; if the year is two digits and there's no plug, it's a Tonawanda block.

that's very interesting to know - thanks John.  It does still stun me that corporate would allow that much discretion on such a key component and not adopt (or require) one or the other as "best practice".

[KurtS]

Best practice?? Back then, the plants and the divisions were all competitive. There was no company-wide vision. They didn't see the freight train coming.....

[melav8r]

Both plants had dedicated foundries nearby, so generally no blocks were exchanged between them. But exceptions could occur.

Post or email me a pic of the pad and I'll take a look.

Heres the link, seller just informed me no front plug so with the stamp and JohnZ's info it's definitely a Tonawanda block, but it has a single digit for the year.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=190222656104&ssPageName=ADME:X:RTQ:MOTORS:1123

[crobjones2]

I have to concur with melav8r - my 350  2388 block is dated E209 - there is no plug
It is only a single year digit- could this be a difference for Tonawanda between 68 and 69?

[KurtS]

I think John may be incorrect on that detail. (gasp!) I don't recall ever seeing a 67-69 block with two digits for the year in the cast date.

[JohnZ]

I'm not positive about the 2-digit year code after '67 (my Corvette focus is '57-'67, and the 2-digit year code was the Tonawanda small-block discriminator during those years); Tonawanda big-block casting date codes used a single digit for the year. They may have changed the small-block date code format during and after 1967.

[melav8r]

I'm not positive about the 2-digit year code after '67 (my Corvette focus is '57-'67, and the 2-digit year code was the Tonawanda small-block discriminator during those years); Tonawanda big-block casting date codes used a single digit for the year. They may have changed the small-block date code format during and after 1967.

Thanks for the info JohnZ, apparently the "T" blocks also use a single digit year code for model year '69, whether cast in 68 or 69, but I concur on the missing front plug. here's a T on the face of another "T" block in the area behind the timing chain. I wonder if that identifies it as a Tonawanda casting?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=260242701219&ssPageName=ADME:X:AAQ:MOTORS:1123

[JohnZ]

here's a T on the face of another "T" block in the area behind the timing chain. I wonder if that identifies it as a Tonawanda casting?

Several of the other pattern identifiers have a "T" as well, so it's probably a Tonawanda casting - can't tell from the photos if it has the front plug or not.

[jmcbeth]

Thanks for the help everyone,but I would still like to talk to someone who has a car that is dated close to mine.

Luke,

If you still need someone with a date close yours, please reply. Mine is 09C. Last digits of Vin are 685955.

[69Z28-RS]

I'm a little late on this thread, but my original unrestored Z28/RS is also an '09C' build week.  I'd love to see some comparatiive information for similar cars.   I'm also in the need of a set of correctly dated '186 heads', as when I bought my car, one head was damaged (a stud had pulled out and been welded back! ).   when I rebuilt the engine in 1977, I sold those heads and bought an almost new set of 'angle plug' heads - which were very hot at the time - for less money then rebuilding the ones I had!  (good deal then, bad for restoration!).  *G*  My engine date is also late August..  so I've been looking for mid-August 1969 dated heads.   I've several sets of '186 heads for ealrier in '69, and also from '70 yr for trade if anyone has date-compatible ones to trade.  Luke and John:  I'd love to compare data with you.  I'm attempting my first image attachment herein, but I don't know if it is going to work.

PS.  Re the relationship of casting to assembly dates:   My '69 302 in my camaro was cast one day prior to assembly.   I've got an original '57 Bel Air (283) which was cast/assembled on the same day (which I've always thought was amazing!)..