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Old 04-13-2021, 02:44 PM
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Another interesting tidbit that may be interesting in this discussion. 20 years or so ago I bought a BHJ ultrasonic cylinder wall gauge. It came with a handful of reference pieces to calibrate it for different cast iron alloys. One of them (designated L-3) was for Pontiac 1965 and later, Olds 1967 and later, GM corporate V-6, Caddy 1968 and later, All V-8 Buicks, and all AMC V-8s. This was not the same for Chevy high nickel/bowtie nor of course for regular chevys.

From this one could guess that in 1965 Pontiac changed to the Buick alloy, followed by Olds in '67 and Caddy in '68. There was no standard provided for Pontiac '64 and earlier and I have always wondered what the difference was.

I have a 64 and 66 block sitting next to each other. Maybe sometime I will get t a chance to wire wheel them both and look at the shine.

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Old 04-13-2021, 03:48 PM
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When I went on a tour of Central Foundry in 1978, that booklet was given to each of us during the tour. So it was probably produced in that general time frame. I vaguely remember being impressed with it. Had a class in college that toured 15 automotive plants in 5 weeks and we had to write a paper about each of them. Central foundry was clean and extremely automated in 1978. In sharp contrast, we also toured a former AMC foundry near Findlay, OH. They were producing castings for Chrysler at the time. It looked like an operation from 1870's compared to central foundry. Many of the "hot" jobs had workers handling castings for 15 minutes with a 45 minute brake between. Everything done by hand, no automation at all other than a few conveyor belts. One of the best classes I had in college.

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Old 04-13-2021, 04:45 PM
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From what I've been able to determine through research, Pontiac cast its blocks and heads of GM-232-M iron. A quick google search shows it's registered as "gray iron," but I've been unable to determine its metallurgical makeup.

Two-bolt main caps were of the same as the blocks (GM-232-M) and many four-bolts caps were too. Some four-bolt caps were, however, constructed of ArmaSteel or Malleable iron, depending upon the model year and/or application.

Intake and exhaust manifolds were cast of GM-14-M iron early on and then GM-232-M later on (mid-1970s onward). A former GM foundry worker told me that 14M was softer and more easily machined and was GM's choice for components expose to exhaust gas.

We'll never know if some runs were of a special alloy or if the metallurgic makeup changed from batch to batch, but for the most part that's what I found Pontiac used. How that compares to other divisions, I don't know.

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Old 04-13-2021, 07:19 PM
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Quote:
Originally Posted by JSchmitz View Post
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.
Had some street driven Pontiacs that had virtually no cylinder ridge at 100k miles.
Bought an original owner 67 executive for the 400 for a GTO build that was missing an engine.
When we pulled the heads off and measured the bores most had worn over .047 and the block had to be machined to 60 over to clean. original std pistons to.
Same engine- the crank measured as new and just a micro polish took care of it.

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Old 04-13-2021, 09:26 PM
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Originally Posted by 455dan View Post
Had some street driven Pontiacs that had virtually no cylinder ridge at 100k miles.
Bought an original owner 67 executive for the 400 for a GTO build that was missing an engine.
When we pulled the heads off and measured the bores most had worn over .047 and the block had to be machined to 60 over to clean. original std pistons to.
Same engine- the crank measured as new and just a micro polish took care of it.
That extra wear had more to do with PMD using both rings being made of plain iron.
Whitmore told me Pontiac switched to single moly top ring, cast iron 2nd ring around 67-68 and the cylinder wear went down dramatically

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Old 04-14-2021, 01:39 AM
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Originally Posted by Dragncar View Post
That extra wear had more to do with PMD using both rings being made of plain iron.
Whitmore told me Pontiac switched to single moly top ring, cast iron 2nd ring around 67-68 and the cylinder wear went down dramatically


Ah , that makes sense. I just assumed that particular block was just softer than the norm

But was pretty sure i had seen info on the rings used in 67 being moly top ring

Dug out my 3rd annual complete book of engines from 1967 and found where I had seen it,
according to it- all 67 400 and 428's had a cast iron 2nd ring and all had a molybdenum filled channel Top ring.

Maybe Pontiac just used up the remaining cast rings on the mid grade 400's
Or my old book could be wrong.

Either way lots of interesting info and history in this thread i am enjoying reading it

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Old 04-14-2021, 01:53 AM
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Ah , that makes sense. I just assumed that particular block was just softer than the norm

But was pretty sure i had seen info on the rings used in 67 being moly top ring

Dug out my 3rd annual complete book of engines from 1967 and found where I had seen it,
according to it- all 67 400 and 428's had a cast iron 2nd ring and all had a molybdenum filled channel Top ring.

Maybe Pontiac just used up the remaining cast rings on the mid grade 400's
Or my old book could be wrong.

Either way lots of interesting info and history in this thread i am enjoying reading it
Maybe it was 66 ? It was right around there at any rate.
Dan was a PMD dealer tech and he took detailed notes of the engines he tore down.
I know a guy who used to do a lot of valve jobs for other people. He was a Chevy guy. Called Pontiac heads "steel".
There not, but they are not the same as a chevy either.

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Old 04-14-2021, 02:25 AM
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Maybe it was 66 ? It was right around there at any rate.
Dan was a PMD dealer tech and he took detailed notes of the engines he tore down.
I know a guy who used to do a lot of valve jobs for other people. He was a Chevy guy. Called Pontiac heads "steel".
There not, but they are not the same as a chevy either.
Wonder if the Chevy Guy noticed that Pontiacs had fully machined combustion chambers so that compression could be kept very consistent.

Can imagine chevies back in the day that had the timing pulled back because a cylinder 'or two" were pinging since compression could vary cylinder to cylinder with those as cast chambers Sorry couldn't resist

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Old 04-14-2021, 03:40 AM
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I agree, great information.. keep it coming.

I'll try to put that main cap under a scope and see confirmation of graphite flakes used. I also sent a message to GM-heritage to see if they have more documents like the on in post no 1.


Thanks to all for valuable information.
Kris.

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Old 04-14-2021, 10:51 AM
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Originally Posted by Rocky Rotella View Post
From what I've been able to determine through research, Pontiac cast its blocks and heads of GM-232-M iron. A quick google search shows it's registered as "gray iron," but I've been unable to determine its metallurgical makeup.

Two-bolt main caps were of the same as the blocks (GM-232-M) and many four-bolts caps were too. Some four-bolt caps were, however, constructed of ArmaSteel or Malleable iron, depending upon the model year and/or application.

Intake and exhaust manifolds were cast of GM-14-M iron early on and then GM-232-M later on (mid-1970s onward). A former GM foundry worker told me that 14M was softer and more easily machined and was GM's choice for components expose to exhaust gas.

We'll never know if some runs were of a special alloy or if the metallurgic makeup changed from batch to batch, but for the most part that's what I found Pontiac used. How that compares to other divisions, I don't know.
Thanks for sharing this.

Who has historical GM material spec documents that spell out composition and/or thermal processes for these codes?

The term "gray iron" does not sound like a "nodular" or ductile composition so maybe there is more to it that can explain all the references to nickel and "steel-like" properties ????

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Old 04-14-2021, 11:25 AM
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Originally Posted by RUDOLFSSON View Post
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.
This is great info.. hope you can provide more.

Do you understand the classes to be a rough indication of yield strength? For example, class 25 gray iron would yield at about 25,000 psi?

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Old 04-14-2021, 11:41 AM
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Can we nail down how these GM numbers relate to common industry standards, and what does the last designation M stand for?

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Old 04-14-2021, 11:44 AM
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Quote:
Originally Posted by Shiny View Post
Thanks for sharing this.

Who has historical GM material spec documents that spell out composition and/or thermal processes for these codes?

The term "gray iron" does not sound like a "nodular" or ductile composition so maybe there is more to it that can explain all the references to nickel and "steel-like" properties ????
I'm sure that GM's specifications are proprietary so total metallurgic breakdown available to hobbyists. It does look like there may be some historical information available for a price. You'll see here that it's listed as "gray iron"

https://global.ihs.com/doc_detail.cf...31&origin=DSSC

When googling GM232M, it looks like GM still uses (or recently used) it to produce various crate engines for marine and/or industrial.

https://www.jblllc.com/wp-content/up...Spec-Sheet.pdf

https://www.suttonirrigation.com/wp-...rial.sflb_.pdf

I did speak with the Heritage Center while researching my Firebird books and they shared what they had on GM's alloys, but it wasn't must more than what's already been linked by RUDOLFSSON.

The materials information I shared above came off a handful of blueprints I was fortunate enough to find and vintage Pontiac engineering information as well as speaking with retired Pontiac/GM engineers and even former GM metallurgists and foundry workers.

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Old 04-14-2021, 11:50 AM
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Quote:
Originally Posted by steve25 View Post
Can we nail down how these GM numbers relate to common industry standards, and what does the last designation M stand for?
At that time I wasn't able to determine what the "M" signified. They did, however, use it behind all alloys, ferrous or not.

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Old 04-14-2021, 12:19 PM
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In this link it shows GM-274-M superseding GM-232-M.

https://global.ihs.com/doc_detail.cf...31&origin=DSSC

I then found this reference for GM-274-M. https://www.eng-tips.com/viewthread.cfm?qid=71816

I can't verify accuracy, but it states:

GM274M is a standard which covers a range of grades, firstly general purpose grades where Minimum Tensile can range from 125MPa to 250MPa. Followed by special purpose grades for Disc Rotors, Pump Bodies, Bearing Caps, Piston Rings and Cylinder Liners. For the general purpose grades, the equivalent standards are:

G125 ASTM A159 G1800 or SAE J431
G150 ISO 185 150
G200 ISO 185 200
G205 ASTM A159 G3000 or SAE J431
G240 ASTM A159 G3500 or SAE J431
G250 ISO 185 250

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Old 04-14-2021, 03:29 PM
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https://www.sae.org/standards/content/j431_200012/

http://www.iron-foundry.com/SAE-J431...-Castings.html

SAE J431 automotive gray cast iron, SAE grade G1800
http://www.matweb.com/search/datashe...e6a6a45bf6fa33

SAE J431 automotive gray cast iron, SAE grade G3000
http://www.matweb.com/search/datashe...0313e3cf96f674

SAE J431 automotive gray cast iron, SAE grade G3500
http://www.matweb.com/search/datashe...1282a9ecc6b35d

Stan

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Old 04-14-2021, 07:30 PM
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The factory blocks I tested for hardness were harder than the MR-1 block I had..

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Old 04-14-2021, 07:55 PM
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Quote:
Originally Posted by Rocky Rotella View Post
...

When googling GM232M, it looks like GM still uses (or recently used) it to produce various crate engines for marine and/or industrial.

https://www.jblllc.com/wp-content/up...Spec-Sheet.pdf ....
Thanks, I saw the same when searching with Google and Bing.

I find it weird that this engine is marketed as using GM2342M yet the spec has been retired/superceded.... maybe GM can reference their own extinct specs but if a customer wanted to know what "made from GM232M" meant for his new marine engine, I wonder who would actually know?

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Old 04-14-2021, 08:35 PM
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Quote:
Originally Posted by Shiny View Post
This is great info.. hope you can provide more.

Do you understand the classes to be a rough indication of yield strength? For example, class 25 gray iron would yield at about 25,000 psi?
I was only looking @ hardness for comparison... and afterwards into tensile

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Old 04-17-2021, 06:36 AM
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What difference does it make how hard or soft the factory blocks are - there's nothing you can really do about it. Both of the '59 389 blocks I've had were very easy to drill/machine - and these were supposed to be better blocks.

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