'M' code block

[James T.]

i have a '72 small block with a date code of M4. If anyone is familiar with Gene Gamache's article on this, or has any info. to ad, please respond.

[Mark G.]

Re: 'M' code block

Jim -

This link, https://www.ncrs.org/forum/archive21.cgi?review=166515

[James T.]

Re: 'M' code block

It is a 3970010 casting with one round head and one flat head screw attaching the 'M4' mark. According to Gene's article, this meant second shift. Also, a separate tag has a '3' indicating that the block traveled on conveyer number three in the Gray Foundery.

[Frank Vincent]

Re: 'M' code block

I have a early '69 with 3932386 block and M39 code.

I wrote to GM and received a reply from the PowerTrain manager and Saginaw Foundry manager. I've also been in contact with Gene Gamache and shared the information I received.
Essentially, as I understand the M system, only the 1st 2 blocks in a "specials" run had the "M" code, while the rest would have the normal date code. In your case, it would have been M3 and M4. If the blocks were approved by GM Engineering, they would have been released to the engine building process. If Engineering did not approve, all the blocks in that run were destroyed.

The "M" code is truly a "one-of-a-kind", as there is only 1 block with that particular casting number and Mcode. If you do some research, you may be able to ascertain when the block was actually produced. In my case, I was able to find 2 other blocks that had the same COPE pattern number and exactly the same characteristics as my block, and they also had the same casting date ... leading me to believe it would have been my casting date.

Since I can only post 1 picture here, I'll post the response from the Foundry manager. I'll post 2 other pictures following that.

[Frank Vincent]

Re: 'M' code block

Page 2

[Frank Vincent]

Re: 'M' code block

Page 3

[James T.]

Re: 'M' code block

Frank, do you known what COPE is an abbrev. for? Jim

[Frank Vincent]

Re: 'M' code block

COPE is the top half of a horizontally parted mold ...

see ...

http://www.swscc.com/making/making_terms.htm

http://en.wikipedia.org/wiki/Cope_and_drag

also ...

http://www.freepatentsonline.com/4779668.html

[Jim Ellis]

Re: 'M' code block

I also have a very early 69 roadster with an "M" code date block, M27. The block casting number is 3932386. This is a Oct.68 built car.

[James T.]

Re: 'M' code block

Jim, have you been able to establish a casting date for your 'M27'? Have you found the pattern number as per Frank's posts?

[Mark G.]

[James T.]

Re: 'M' code block

The pattern serial number on this block is 26. Does anyone have this pattern number from a '72? If so, what is your date casting?

[Jim Ellis]

Re: 'M' code block

Jim

My pattern number is 12, I have not been able to establish the casting date.

[Dan Pepper]

Re: 'M' code block

For further reference, here are a few shots of my '69 L46 M code block casting #''s and stamp pad.

[Dan Pepper]

Re: 'M' code block

...another photo of the block casting#'s...