Guys Has anyone here ever seen any literature that explains what GM was up to regarding 4" bore 302/327/350 blocks for 1969 model year? I know that there was a big shakeup in 1969 where GM changed the structure and put all drivetrain into a division, and from that time forward casting numbers appear to be shared, for example 3970010 blocks appear across Tonawanda, McKinnon and Flint engine plants from mid 1969. This may partly have been to do with strikes that also see the 1969 model year continue until around December 1969. But what I have seen so far: Early 1969 model year (about August 1968 - December 1968) - Flint uses 3932386 blocks. Then this casting number pops up in December 1968 on McKinnon cast and assembled blocks (I have a few here cast in Canada and with Canadian assembly stamps on them). At the same time and moving forward into 1969 calendar year Tonawanda is using 3932388 blocks but I have found Saginaw cast 3956618 blocks machined and assembled at Tonawanda around Feb-May 1969. I have a feeling Flint replaced 3932386 with 3956618. Then they all start to use 3970010 from around May-July 1969.
I haven't fully researched to see what else is on their site, but I know Mortec.com has a healthy listing of GM casting numbers and sources.
I would suggest the "Chevrolet by the numbers" books by Alan Colvin. These are the best I have found for Chevrolet I.D.
There are several reliable sites to check Mortec being one of the best along with http://www.nastyz28.com/sbchevy/sblock.html Others being http://outintheshop.com/faq/casting/castings2.html New one to me that I haven't used but looks interesting https://www.enginerepairshop.com/chevy-casting-numbers.html Still I have never understood the pee on your shoes because you have a certain casting number on a 350 block or what year it was cast for or what it originally went into unless one ,you are hunting for "that specific block" for a restoration or you are hunting for a specific block because it has certain features that others don't or you are hunting a 4 bolt main block. Although you might impress a few mouth breathers if you were able to sit in your lawn chair an give them the Ya, the block is a 69 327 big journal block at a rod trot.
Thanks guys. There is heaps of sites and books around that explain what the casting numbers are (some more correct than others), but I am after more of what went on at the engine plants behind the scenes leading up to the GM drivetrain re-organisation in 1969. My goal is to understand the reasons why in Australia we got the engines we got in our Australian Muscle Car, the Holden HK GTS327 of 1968-96, HT GTS350 of 1969-70 and HG GTS350 of 1970. In fact some of our specification engines here do not exist in US vehicles (like a 1969 passenger 4BBL 327) but they do use standard parts from mainly Tonawanda and McKinnon/St Catharine's engine plants. I have had a quick look at the Colvin books but he doesn't go into huge detail on the specific differences between engine plant casting differences and why they changed when they did. I have a fair amount of McKinnon/St Catharine's information but looking to see if anyone here has seen anything about what was happening at Tonawanda and Flint that time that makes the block casting numbers change and even shift plants. The sort of stuff at this link attached is what I'm after, I asked Greg where it came from and it was developed by an ex McKinnon worker who was a history buff, you can see that even a few small words like what is against 1969 here explains why in Australia we got Tonawanda 350 engines early on but later changed to St Catharine's engines: http://hotrod.gregwapling.com/chevrolet/mckinnon.html
On a purely mechanical aspect, I think what led GM to the changes for the 69 and up small blocks were the years of abuse on the drag strips, as well as the Z/28 Trans-Am engines and the need for machining blocks for four bolt mains (among other things). I'm sure GM listened to input from people like Traco, Penske, Yunick, Jenkins, etc. considering they were funneling money to them for development purposes.
I have no doubt the introduction of the 1969 year model engines with 4 bolt mains was a result of input from those guys, but initially the casting plants had their own casting numbers for essentially the same thing: Flint 386 block, 186 heads, and looks like migration to the 618 block after about December 1968. Tonawanda 388 block and 041 heads (although Tonawanda do not appear to have done 2.02/1.6 valve versions so nothing more powerful than the L48 350/300 but still 4 bolt). But later in 1969 model year, towards the middle of 1969 all plants seem to change to the one casting number, the 010 block. There is probably going to be minor variations between 386, 388, 618 and then the 010 with improvements as time moved on and I'm interested in that too - Alan Colvin can probably solve that one for me, will study his latest books to see if he goes into any detail. However I'm more interested in the mechanism behind the changes - like why Tonawanda are machining and assembling engines using Saginaw cast 618 blocks in early 1969, why 386 blocks suddenly appear out of McKinnon late in 1968. I suspect some of it may be GM covering their bases so strikes didn't shut down the business, and whether this 1969 business restructure was planned or made as a result. It is well documented that 1970 model vehicles didn't appear until around January 1970 rather than September 1969 - due to various factors including strikes they ran the 1969 models through to the end of 1969. Incidentally this is why the 1970 Camaro gets called the 1970 1/2. Hence why I asked the original question, just thought some of the older guys here may have seen some info on it somewhere.
From my copy of Chevrolet By The Numbers 3932386 Identical to 3932371 block with changes to cylinder wall and water jacket casting cores. Used from August 68 to January 69 3932388 Tonawanda cast and built, probably identical to the 3932386 block . Used as a 350/300 only. Casting dates from September 68 to December 68 3956618 Identical to 3832386 with minor casting changes. Generally used in low power 327 and 350 3970010 Completely new engine case design. used up to 1975. Casting started in late April/early May.
Thanks VINFAB. Will have a better look at Alan's books, I have only skimmed through them at a friend's place. I do know that he has 3932388 wrong though as I know it was also used on the LM1 engines in 1969 (350/255) and also on some L65. I have seen 350/300 cast as late as July 1969 using this block. I believe Tonawanda used this casting up until the 010 replaced it.
The Jalopy Journal
