[RUDOLFSSON]

Hello friends..

Does anyone have reliable documents or information on the metallurgy of our V8 Pontiac blocks... I assume gray iron... ?

I was planning on doing a hardness test on a main cap this week to ID the type of gray iron "quality".... and maybe a simple drop test afterwards for comparison between cap and block for similarity confirmation.

Here's an interesting read I came across while searching..

https://www.gmheritagecenter.com/doc...n-Castings.pdf

Thanks in advance,
Kris.

[Tom Vaught]

Some blocks were cast up with the base metal cast iron material, but had a better grade of Nodular iron main caps installed when 4 bolt main caps were used.

Tom V.

[steve25]

Thanks for sharing that info big time!
I can't believe I have never come across it in all of these years!

[Shiny]

Originally Posted by RUDOLFSSON

Hello friends..

Does anyone have reliable documents or information on the metallurgy of our V8 Pontiac blocks... I assume gray iron... ?

I was planning on doing a hardness test on a main cap this week to ID the type of gray iron "quality".... and maybe a simple drop test afterwards for comparison between cap and block for similarity confirmation.

Here's an interesting read I came across while searching..

https://www.gmheritagecenter.com/doc...n-Castings.pdf

Thanks in advance,
Kris.

Thank you for sharing that document, Kris.

It is a blast from the past.

My degree is in metallurgical engineering but I never worked in automotive nor a "primary" metal industry nor with cast iron so my knowledge isn't going to help much beyond what I can read in the book.

I did have a job interview scheduled with a Ford foundry when I graduated (1976) but there was a strike or something and they cancelled on me!

I plan to read the brochure with interest as I am unfamiliar with pearlitic microstructures in cast iron.

A quick glance tells me the GM Central Foundry had some unique alloys and a massive heat-treating and machining facility.

All I can say is I'm interested in the specifics of the engine block alloys but the information doesn't seem to be in that brochure. Like steel, there is a wide range of alloys and properties labeled "gray iron".

Hopefully someone can share more history about Pontiac's engine blocks and alloys. I have no clue if Pontiac had their own foundry or relied on this GM Central Foundry for all cast iron parts. I have read there were variations in engine block nickel content but never saw any details. The history is interesting for me as it is such a huge part of the story of the metal industry in the US.

Hopefully forum members that worked in the auto industry will point to more Pontiac manufacturing history and details.

I'm also interested in your hardness data if you are able to get that done.

Mike

[Elarson]

I am by no means a cast iron expert. But one interesting thing that I ran across is that a wide range of strengths can be had from the same chemistry. It is very dependent on the rate of cooldown after initial solidification. If it's left in the mold a longer time, it cools more slowly and finishes out at a softer, lower strength.

Again...I'm not an expert but that's an important part of the equation.

Eric

[Shiny]

Agree with Eric.. I am also no expert but was taught some principles 40+ years ago.

The cooling rate affects both the composition and the morphology of the microstructure. It is the microstructure that controls all the properties.

Think of it as carbon is soluble (dissolved) in iron at high temperature but wants to come out of solution and be carbon at low temperatures. The microstructure is all about how the carbon comes out of solution.

Fast cooling rates can "lock" the carbon in solution and not give it time to precipitate in big chunks. For steels (lower ranges of carbon content), the same is true but the end game is more about iron carbide particles than "graphitic" (pure) carbon. In cast irons, there is "excess" carbon relative to steel.. this means cast iron microstructures can be all over the map with mixtures of "steel-like" characteristics. The heat treating described in the GM brochure appears to be all about generating "steel-like" microstructures in gray iron castings.

[steve25]

I recall that at least in terms of Pontiac blocks ( maybe all iron GM blocks back then?) once they where demolded there where aged for 2 weeks before machining.

[RUDOLFSSON]

Ordinary #3 2-bolt main cap from a '74 block 48XXXX block results from our Mitutoyo hardness tester 87-88 Rockwell B .. => 172-176HB (3000kg@10mm)

Similar to gray iron class 20 / 25 ... now I need to do a simple drop test and see if cap and block are the same.


Kris.

[Skip Fix]

All my 409 Chevy blocks have"Armasteel" cast into the main caps.

[61-63]

Originally Posted by steve25

I recall that at least in terms of Pontiac blocks ( maybe all iron GM blocks back then?) once they where demolded there where aged for 2 weeks before machining.

I would be interested in knowing where you got this because I recall several instances (perhaps numerous?) of block casting dates being closer than that to car build dates. No I can't specifically point you to one too many years, too many discussions on here and at Norwalk, etc., etc. And my memory may just be failing me, which is certainly possible, but I'm pretty sure I've seen or heard of instances where a block was cast, say, on Monday and the engine made up on it was in a car by Friday - that sort of thing. I may even have owned one.

[Half-Inch Stud]

PMD blocks were not gray iron, probably ever (never). Chevies Bid and Small had Gray Iron. Upper ring ridge wear is a tell-tale.

PMD Heads were same naterial as PMD block.

PMD Exhaust Manifolds were Chevy Block material: Gray iron.

I wonder what PMD used for intake manifolds......!

[Dragncar]

Pontiac blocks "shine" compared to a Chevy. If you wire wheel a rusty Pontiac block or heads they start to have a little silver shine to them.
A chevy (grey iron) stays flat and dull.
Cadillac blocks are of good iron and shine also. More nickle.

[4zpeed]

Thanks Kris, I've wondered on occasion if you were still investigating metallurgy, referring to the other thread on cast iron heads.

How did you ever find that link, "I searched the world over and thought I found true love, it met another an pfft it was gone, lol".

This file is a awesome bit of insight into the world of GM and their engineering efforts in all of the various metallurgy processes.

Some early cheby blocks apparently do have a luster but for the most part yea they're drab, early Olds stuff has the bling factor too.



Frank

[steve25]

It's my understanding that all Exh Manifolds must be made of Dutlie iron, not plain Gray iron.

It's also interesting to note the tempering that takes place just thru usage!

When I port the Exh side of iron heads, and especially on the roof where away from the main body of the heads there's far less iron mass, grinding thru the first 1/32 to 1/16 of a inch is hard to do and after that metal removal is then just like grinding on any other part of the head.

This is also far more noticeable on the later heads that had to deal with pumping out Exh thru converters and there added restriction and heat!

I also agree that Pontiac blocks have more Nickle content then some other GM brands and especially SBC heads!

I also wonder if earlier blocks other then the 60s SD blocks might have had more ?

In terms of hardness and a machine shop I worked in, I recall 3 sets of late model SBC heads that we loaded in the Steel shot machine to clean them good on the customers request and when the timer turned the machine off and we opened up the load in doors every sharp edge was rounded off to the tune of 1/8" and the Heads where unusable!
Some great cast iron that was!

[JSchmitz]

You all have probably heard Chevy people talking about old LT1's etc. having "high nickel blocks". My old engine builder (now retired) told me that all Pontiac blocks are high nickel content.

[Half-Inch Stud]

I can look up most of the PMD metals used. Exhaust manifold might be ductile iron.

['ol Pinion head]

Agree with 61-63's above comments in respect to tighter dating. Have seen several such instances of tight engine block dating out of the home Pontiac plant build. This was in the '64-66 years & on higher volume coded engines.

[RUDOLFSSON]

Thanks for all your input...

@ Half-Inch
I'd appreciate it! ... I'm doing an in depth investigation on my lifter bore braces and the forces that one might encounter.. so far I'm about 100 pages into it !


Kris.

[Shiny]

Sounds like the consensus is Pontiac blocks were nodular.

I hope HIS can find and share alloy and/or process specifics.

As to nickel, I'm interested in learning the facts. Online blurbs suggest nickel can help "toughen" (less brittle) nodular iron but it's expensive so would be good to understand the alloys used and learn the "why". Material properties with and without the nickel would spell it out.

I can see smaller parts (caps, rods, cranks) run through heat-treating ovens (the Armasteel thing) but I'd be surprised if engine blocks were heat-treated. Pontiac never used the term "Armasteel" for blocks, right?

[shermanator2]

Originally Posted by Dragncar

Pontiac blocks "shine" compared to a Chevy. If you wire wheel a rusty Pontiac block or heads they start to have a little silver shine to them.
A chevy (grey iron) stays flat and dull.
Cadillac blocks are of good iron and shine also. More nickle.

Originally Posted by Half-Inch Stud

I wonder what PMD used for intake manifolds......!

About a year ago I wire wheeled a '64 Tri-Power manifold and noticed it really shined compared to a lot of other cast iron I have wire wheeled.