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Posted by: jjohnsonjo ()
Date: November 19, 2020 06:10AM

flat_six Wrote:
> Interesting question Tim and one I’ve pondered lately. Just finished building a 180 motor with NOS heads. What I did notice about these is that, due probably to the late production timing of the heads, the quality was terrible.
> The casting was hideous - presumed to be due to tooling that was on its last legs and maybe even foundry workers who were not experienced with setting up parts for that discontinued Corvair. Core offset, tons of excess flashing, a gaping hole in the intake manifold that I had to pay to be welded shut. Evidence of weld repair on both heads.
> I also had to chase every thread in both heads so the bolts would go in. Could the cylinder head shop in Tonawanda have worn out taps by then?
> So I wonder if the seats in these heads were installed well, at least as good as seats that were done during the height of production.
> Time will tell Tim! ????

I've have heard from a few other guys over the years that the bronze exhaust valve guides in those late replacement service heads was not the same as normal production heads. They start to squeak and wear out very early. These heads were less than $100 bucks without valves at a Chevy dealer back in the day. Keep an eye on your guides if you haven't changed them.


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Posted by: JimBrandberg ()
Date: November 19, 2020 06:11AM

I have some NOS 140 heads and plan to simply deflash and put into service.

I believe it's the 356 aluminum losing it's temper due to heat cycles, especially severe ones, that's responsible for the aluminum losing it's grip. An essentially new head that's not experienced heat cycles should not have gone soft.

Of course a deeper seat with a tighter press fit would have more holding power but I'm not about to go that route on a new head.

Some folks have some opinions about a tighter press fit eventually relaxing but I don't know enough to form an opinion.

Racer Jon Brakke was a firm believer in getting old heads heat treated to restore the temper but it's A LOT of work.

Jim Brandberg
Isanti, MN

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Posted by: REM654DPG ()
Date: November 19, 2020 10:30AM

Nirvairna asks: I've noticed many seats in newer cars are powdered metal - what do you think of them?

I think those are good high-quality seats too and are comparable to the ones I use. I may look into trying a set of them depending on what the pricing is.

Regarding NOS parts, this is what I have found to be true at least from my experience. The majority of them, especially engine and diff parts have some kind of defect or problem with them. Many of them ended up on the dealer shelves as returned defective or unwanted parts for some reason or another and then ended up in a liquidation and then into someone’s collection. I’m not saying that all NOS parts have this issue – especially cylinder heads – but, you should always meticulously inspect, measure and evaluate any NOS engine/diff part before you buy it because you may find something that renders it questionable.

Regan Metcalf
Portland, OR

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