<VV> Dang 40 yr old aluminum !!!!

[Harry Jensen, CORSA Executive Secretary]

Hello--

The engine in Jon Brakke's Corvair SCCA race car used to loose compression 
in a couple of cylinders after a couple of sessions. We used to religiously 
do a leak down test and if the compression was down, we'd pull off the 
heads and lap in the valves. Jon's theory was the seats were moving slightly.

He eventually had the heads heat treated. I'm pretty sure the heads use the 
aluminum alloy 356 which then is heat treated. After many, many years of 
heat cycles, the aluminum losses its hardness.

After the heat treating, we never had a compression problem due to leaking 
valves again.

--H


At 09:44 PM 3/5/2008, Kent Sullivan wrote:
>Barry, make sure that this shop is using the state of the art, seat-wise:
>Slightly taller and slightly larger in diameter. They won't fall out that
>way, pretty much guaranteed, because there is much more grip than the stock
>seats. The shop will need to cool the seat and heat the head to get them in.
>
>This is something, IMHO, that Chevy should have done in the first place...
>Since dropped valve seats on the hi-po engines (turbos especially, and 140s)
>has been common from the beginning.
>
>--Kent
>-----Original Message-----
>From: virtualvairs-bounces at corvair.org
>[mailto:virtualvairs-bounces at corvair.org] On Behalf Of D. Barry Ellison
>Sent: Wednesday, March 05, 2008 7:24 PM
>To: Virtual Vairs
>Subject: <VV> Dang 40 yr old aluminum !!!!
>
><snip>
>
>So, the bad seat areas will be welded up tomorrow, taken to the machine shop
>for 6 new exhaust valve seats and one more intake again.  After that, we'll
>weld a small bead around them to hold them.  (Is there a real need to run a
>bead around the entire seat or is two 1/4" beads 180 degrees apart enough?
>3 beads at 120 degrees?)
>
>Yes, we'll check the valve guides, especially of the ones that dropped.
>
>If it happens again, I promise you I will sell everything but my convertible
>VERY CHEAPLY and go play with something else, most likely a Factory Five GTM
>kit car!Barry Ellison
>... more than my share of dropped valve seats.  sassafrackin' frickin' 40 yr
>old aluminum!!!
>
>
>
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|--------------------------------------------------------------
| Harry Jensen  mailto:corsa at corvair.org
| CORSA Executive Secretary
|
| Corvair Society of America (CORSA)
| P.O. Box 607, Lemont, IL 60439, 630.257.6530  fax 630.257.5540
| http://www.corvair.org
|--------------------------------------------------------------