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Re: Identifying A Hack Job On A Head
Posted by: BobV66Vair ()
Date: May 16, 2017 09:31AM

First, the hardness test Jim mentioned is called a Rockwell Hardness Test. It is usually a small tool that smacks the metal at a specific impact (distance & force) and then the resulting dent is measured for depth. Very hard steel, like that used in concrete pumpers, is a Rockwell 90. That is really hard and results from a steel alloy. I worked for a gear manufacturer (Perfection/Zoom) in the 70's and 80's. The Zoom gears were very hard but a top fuel drag differential builder would always re-treat his gear sets. All 9" Ford by the way. He said his experience made him only use one specific hardness and ductal characteristic. This was a long time ago before modern testing and treating were perfected and top fuel gears were custom made.

Second, I may be fuzzy but Aluminum is hardened by heating and slow cooling. The opposite of steel, fast quenching aluminum actually makes it softer. Our engines go through this heat/cool process every time we shut them off. It seems to me that the heads may get too hard if anything. I believe they go through expansion and contraction constantly as we drive them so it is actually that heat/expansion cool/contraction that causes the most problems. GM must have figured the metallurgy out since they last for 50 years. I am not sure a heat treat specialist could get that close, particularly since they don't know the OEM specification on the metal. Ray does install only deep seats and he actually uses wider seats so he machines the head to accept them. I forget what the steel is but it's something exotic. Artwork.

I was glad to see that the problem heads Lawrence had were not done by Ray! He has been working on mine for a few months now and I expect them to be artwork when complete. I would be very concerned if they are not.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Identifying A Hack Job On A Head
Posted by: JimBrandberg ()
Date: May 16, 2017 09:56AM

If I remember right, Corvair heads are 356 aluminum alloy.
I thought heating and quick cooling was the process in heat treating to restore the temper. I hope I'm not the one who's fuzzy.
Yes it was a Rockwell test.
My old machinist said one pair of heads I had were like cutting butter, they didn't have the good chips when machining.
Jim Brandberg
Isanti, MN
CorvairRepair.com

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Re: Identifying A Hack Job On A Head
Posted by: mspeters ()
Date: May 16, 2017 10:31AM

I suspect Bob is thinking of aging. But the alloy IS quenched prior. Heating it up is called solution treating and locks in the alloying elements as a homogeneous solution when quenched.

[www.bodycote.com]

see pg 5 of this: [www.afsinc.org]

356 does seem likely

Matt Peterson
Ada, MI
65 corsa vert 180hp

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Re: Identifying A Hack Job On A Head
Posted by: toytron ()
Date: May 17, 2017 05:29AM

Matt is on the right track. Here at Arconic (formerly Alcoa) the heat treating processes sometimes involve "ageing" where gas(s) are introduced into the heating process that aide in strengthening the alloy. Of course our furnaces are huge and we do many ingots or slabs at one time. Not only for the automotive but aerospace industries too.

At Caterpillar they also use Some exotic gas combinations to heat treat their drive wheels for their large dozers (steel) and their clutch plates.

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Re: Identifying A Hack Job On A Head
Posted by: toytron ()
Date: May 17, 2017 06:38AM

Well after talking to someone more knowledgeable than I on this topic I stand corrected. We do not work with casting alloys as much in this location so the aging process is mostly time and temperature for casting alloys. We do use time and temperature here but it is different for casting of cylinder heads. So that just goes to prove that you need to know that the person whom you work with knows what they are doing with your parts.

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Re: Identifying A Hack Job On A Head
Posted by: BobV66Vair ()
Date: May 17, 2017 08:51AM

mspeters Wrote:
-------------------------------------------------------
> I suspect Bob is thinking of aging. But the alloy
> IS quenched prior. Heating it up is called
> solution treating and locks in the alloying
> elements as a homogeneous solution when quenched.
> [www.bodycote.com]
> ent/solution-and-age/aluminium-alloys.aspx
> see pg 5 of this:
> [www.afsinc.org]
> 356 does seem likely


Good stuff Matt. Now I know the correct term for the heat and slow cooling cycle. I had just heard it all called heat treatment. This does show the engineering that went into the Corvair engine parts. I would not mess with it.

Bob Vinnacombe
Sandy, Oregon
1965 Corsa 140 stock
1966 Monza Soon to be race car
1968 Monza Parts for now

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Re: Identifying A Hack Job On A Head
Posted by: tknobby ()
Date: May 21, 2017 01:55PM

I only heat treat heads that have been run excessively hot, machine like the metal is "gummy", required excessive welding to repair or the customer requests the heat treat. The average head I rebuild machines out just fine.

For iron seat install I only heat the head to 300F and use .008" to .010" interference. Then stress relieve the head after it cools. Heating to 500F will cause the head to begin to anneal. I do Not peen any aluminum around the seats. This is Not needed. At least on my work. For bronze seats I use .005" to 006" interference fit.

T...

Tom Knoblauch
San Antonio, TX
AmericanFlat6.com

'64 Spyder Vert Big Valve heads EFI Custom roller cam front disc brakes on 2" drop spindles
'65 Vert 95 EFI 4spd
'65 Monza Coupe 95 w/ Thomas Tribute 110 heads 2 2bbl 40MM Webers 140 exh tubes and logs PG w/ high stall Converter
'66 Monza Coupe 3.0L EFI 4spd
'68 Monza Coupe 140 3.0L EFI Slide Throttle 4spd

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Re: Identifying A Hack Job On A Head
Posted by: Max Roeder ()
Date: May 22, 2017 02:43AM

mspeters Wrote:
-------------------------------------------------------
> Do we know what alloy vair heads are?
>
> Too much press fit would cause the heads to relax
> back close to its yield strength due to the
> excessive hoop stresses. Think of the horizontal
> portion of a stress-strain curve...


Interesting comment on the stress strain curve. Could you expound on or provide an example of the curve as it would relate to the compressive stress strain/ time in the seat region on the corvair heads. Also possibly a comparison of these factors as related to the series of 356 cast alloy variants.

I've been trying to identify the specific 356 aluminum requirements for the heads and have only been able to find the "356" on any drawings. If you or anyone else has knowledge of how close GM held their alloying control I would be interested in knowing more. Also was there ever any thermal treatments applied to the 356? I'm guessing a T5 or T51 post cast treatment was applied for machining and maintaining dimensional control. But Like I said I have never been able to nail down any real standard specs for the 356 heads. Look at the standards for Aluminum 356.0-T51, Sand Cast:

[www.matweb.com]

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Re: Identifying A Hack Job On A Head
Posted by: toytron ()
Date: May 22, 2017 10:26AM

I wonder if I brought in a sample to work if someone in the lab would test it for me? I will have to see if I have a scrap head laying around.

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