The Real Difference's in a 75/76 Block?

I've been building Buick's for a lot of years and have always heard the stories that the "blue" 75/76 blocks have thicker cylinders and are stronger. That being said, I've never used one or checked one. So, those of you who have actual proof and experience with one, what are the real differences in a 75/76 block? Cylinder's, deck height, main bearing area, etc., or are these simply urban legends? Yes, I have one and am deciding if I want to use it for my next build. Looking forward to the responses.
Thanks
Brent

 

They do in fact weigh more ,...the main webs are visibly thicker in places,...the block has a much different coloring after cleaning and baking,...BUT,.. they are common to have core shift,..Olds was casting them for Buick

 

I had 4 sonic checked to other week a 74 75 and a 76,.. the 75 was best the 76 was garbage and the 74 was decent,...I'm going to use the 75 for my 494 build and a 400 it 430 block for my 871 build

 

Olds was just casting the 75 and 76 blocks? Also was the service replacement block a 75, 76 production block?
I'm guessing the Olds block had core shift issues?

 

First I have ever heard of that... When I discussed this with Dennis Manner some years ago, he did not mention any other suppliers.. but did say that as the foundry tooling would wear out, they would regularly replace it, and because the engines were being run leaner and leaner (hotter) all the time, that as the new patterns were made, the deck and cylinder wall thickness was increased to better handle the heat. Because not all the tooling was changed at once, and because it was right at the end of the production run, many 76 blocks were cast with the old tooling.

Yes, you will find some 76 blocks that are as much as 11 lbs heavier. When I suspect I have one of those, first thing I do is put it on the scale..

You will find some thicker blocks, in every years, but typically the really thick ones tend to be only 76 vintage.. in my experiences But they are actually really rare, it's just as likely to find a thin 76, and the core shift issues were no better or worst than any other year.

The 75 blocks are lumped into this because of the blue paint thing.. but in my experience, the blocks with the extra meat, that goes beyond just the normal variations, were all 76's.

I can find excellent blocks in every year, and have. You get a nice centered casting, odds are it will show up with a bunch of sonic numbers around .250. Also universal is that the thicker parts of the block exactly the opposite of where we want them... the major thrust side is always the thinner of the two load bearing surfaces.

JW

 

I'm not to updated on foundry manufacturing.
I can see the sand casting molds or whatever they used wearing out from constant pouring of melted iron. I would think the mold of the blocks themselves wear out 2nd? Not sure what they were made of.
Custom tooling to machine the molds wearing?
Any idea to just how many molds were used in the production day of the BBB and how many made in one day?
On top of the thicker cylinder walls and decks was the little thicker mains done for the same reason?

 

So what do the beefier blocks in at as compared to the more normal blocks

 

Sand casting mold parts are relatively inexpensive but each pour is labor intensive. The inner cores or what becomes the water passages are subassemblies made of formed sand, later to be broken up and shaken out after the pour. The core assemblies are held together by what is later capped with the Freeze plugs. While sand casting tolerances are pretty loose, I'm surprised to hear Jim mention the tolerance stack-up error is opposite of what would have been ideal for material thickness. In hindsight, that was an engineering/casting issue that probably could have been a pretty easy and inexpensive correction.

 

Thicker decks and cylinder walls.

JW

 

I have used the 75 blocks for years,never used a lifter girdle,never broke one.This with around 800 horses.Bruno.

 

Forgot a word. What do the beefier blocks tip the scales are actually....like what does one physically weigh, how many pounds

 

I have designed a quite a few aluminum sand casted parts. Never did a steel casting. Mostly I do aluminum die castings, and plastic parts.. I can only say from the times I visited foundry suppliers, and speculate what happened 50 years ago. Sand is recycled and sifted but only back to the main mold halves, The inner core parts i saw were a different color sand and have some form of bonding agent to keep it together. The main halves are littereraly hand packed sand in a 2 part metal frame and the molded form is carefully removed. Then the core parts are manually installed and the frame halves are put together for a pour. The factory is a dirty, hot, loud, smelly environment. The castings cool off while moving down the line before they are violently shaken to remove the sand. I have no idea if casting core shift or scrap rate was an issue for the original factory machining. 1970's GM probably didn't care too much if it could be overbored. I'm guessing GM had multiple vendors for their castings. The company i work for uses multiple foundry services from all over the world, USA, China, India etc, they all have their challenges.

 

Here is a good blog on the history of the Buick Foundry in Flint. It was a huge multi building facility, that operated from 1926 thru 2011. I would be very surprised if Buick was outsourcing engine castings.

http://buickcity.blogspot.com/2013/03/foundry-70-1926-2011.html

 

Interesting read about the old foundry. The buildings today are used as an assembly plant for trucks.

 

That could be. If so... sad

 

Yup, here is some info on both sites in Flint... for those interested

https://en.wikipedia.org/wiki/Flint_Truck_Assembly

https://en.wikipedia.org/wiki/Buick_City

JW

 

I believe at one time, someone was selling salvaged red bricks from the demolished Buick City buildings as souvenirs.

Tommy