# Pontiac blocks - deterioration?



## bignuk1 (8 mo ago)

A garage full of parts came with my cars and I am trying to sort out what is sellable and what is junk. I pulled 4 blocks out and in trying to id them noticed 3 of 4 had what appears deterioration of the metal at the back of the block towards the distributor but inside the block. Is this normal or are these junk? Thanks


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## armyadarkness (Dec 7, 2020)

iT'S JUST THE WAY THEY WERE CAST


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## armyadarkness (Dec 7, 2020)

Sorry for the caps


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## geeteeohguy (Feb 2, 2008)

Agreed. Casting 'birthmarks'. A non-issue and they've been there since the foundry.


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## Sick467 (Oct 29, 2019)

I've only tore down about 10 engines in my career as a enthusiast. I have never seen a lack of casting material like those. Usually it's the opposite, some extra flashing material that can be ground of to make it pretty or to help the oil flow ever so slightly better. I'm not saying they are not good cores, I'll let the more experienced chime it, but I would not consider them for souped-up build. You might ask "why" and I'd have to say because "I don't know any better". Even if they are good-to-go, perception of a problem can reduce their value.


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## armyadarkness (Dec 7, 2020)

Ironically, often what's considered "missing" material, is "extra" material.


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## Sick467 (Oct 29, 2019)

This is what I have seen on the three 400 blocks that have come through my shop (pic borrowed from the net)...










The extra flashing is seen, above, between the opposing rear lifter holes as a lighter colored ridge. The OP's photos show holes or voids in the rear wall. After flipping through photos, on the net, of our beloved blocks, I see several with holes and voids in that area...must have been a common occurrence. I would still consider it to be a less than desirable casting. I can't begin so suggest that it won't hold up and I would certainly not throw them out.


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## armyadarkness (Dec 7, 2020)

No doubt that many are better than others!


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## redhorse719 (Jan 9, 2019)

bignuk1 said:


> A garage full of parts came with my cars and I am trying to sort out what is sellable and what is junk. I pulled 4 blocks out and in trying to id them noticed 3 of 4 had what appears deterioration of the metal at the back of the block towards the distributor but inside the block. Is this normal or are these junk? Thanks
> View attachment 157399
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> View attachment 157400
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Casting flash, not a problem unless it breaks loose on a fresh engine. Carefully remove it with a die grinder before hot tanking.


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## Baaad65 (Aug 29, 2019)

I don't like how that hole climbs up the dizzy wall either, especially in the lifter galley I want more not less with Pontiacs known for breaking there.


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## 1971LemansWisc (Apr 18, 2021)

Late '70 400 Block - same hole in the back wall.

The Casting Flash between Lifter Bores isn't bad.


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## bignuk1 (8 mo ago)

Thanks for the input. I will sell as is and not scrap them.


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## lust4speed (Jul 5, 2019)

I've seen more blocks looking like Bignuk1's than being completely filled in back there. I just take a die grinder and remove the flashing back to the thicker area.

One thing is for certain, that is the way those blocks were born and they haven't got worse with age. Figure they made it 50+ years being like that.


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## Jared (Apr 19, 2013)

My 461 was like that as well. If you zoom in and look at the rear of the block, mine's similar. Len Williams left it like that so I'm sure it's fine.


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## armyadarkness (Dec 7, 2020)

lust4speed said:


> Figure they made it 50+ years being like that.


That's what I'm thinking


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## Baaad65 (Aug 29, 2019)

Looks can be deceiving, something else learned today 👍


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## PontiacJim (Dec 29, 2012)

armyadarkness said:


> That's what I'm thinking


You can deburr the casting flash using a die grinder/sanding rolls. I never did this nor even thought about doing it in the past. I did do it on my 455 block because I read it can prevent any casting flash to break off and fall into the engine and smoothing the edges out can help to prevent any stress cracks as well as help with oil return.

With the millions of engines Pontiac cast, when was the last time you hard of one going south because the casting flash broke off and damaged the engine? So it is one of those things I feel can help to make you sleep better at night, but may not make a difference one way or the other - and makes for good conversation in a group of motorheads that you deburred the lifter valley of casting flash and it cut 1/2 second off your 1/4 mile times.


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## Sick467 (Oct 29, 2019)

Along with cleaning up the casting flash around the lifter bosses, I have been advised by a long-time Pontiac drag racer to open up all the oil return holes in the valley. I have opened them up with a die grinder by about 1/16th inch or a bit more, but try to open them up towards the slope that the oil is running down to begin with. Then I chamfer the hole opening up slightly to eliminate the sharp edge. You can see one of them in Jim's photo...dead center in the photo. It's just one of those things that sounds good to do without any study to prove it. I sleep better for it.


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## Noangelbuddy (Dec 6, 2017)

bignuk1 said:


> A garage full of parts came with my cars and I am trying to sort out what is sellable and what is junk. I pulled 4 blocks out and in trying to id them noticed 3 of 4 had what appears deterioration of the metal at the back of the block towards the distributor but inside the block. Is this normal or are these junk? Thanks
> View attachment 157399
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> View attachment 157400
> ...


I would have been wondering the same thing. It amazes me that blocks are made using sand casting molds. I’ve seen the ”how it’s made videos” and know it’s been done this way for decades. It never would have occurred to me, but then I am still in awe of vinyl records (some of you may remember those) and the quality of sound picked up by a needle.


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