<VV> More on valve seat failures

[jvhroberts at aol.com]

 On this, we fundamentally disagree. Far too many of us have had dropped seats, even on factory heads that have never been abused or improperly repaired. Not all of them, but far more than would be considered statistically acceptable. As such, far too many of them don't run forever. And, statistically speaking, a sample of 1 isn't meaningful. 

I've dropped seats on about half of the Corvair engines I've owned, all 140s, except for a 110 which also dropped an intake. 

Look at how long this thread has become, there's your evidence!! 

 

John Roberts
 

 

-----Original Message-----
From: Mark Durham <62vair at gmail.com>
To: jvhroberts <jvhroberts at aol.com>; sheridanma1966 <sheridanma1966 at gmail.com>; virtualvairs <virtualvairs at corvair.org>
Sent: Wed, May 9, 2012 10:23 am
Subject: RE: <VV> More on valve seat failures


John, I agree, and if there are problems with seats in a Corvair head,
there are modern day seats available that should fix the problem. But,
my point is even though GM may have cheaper out and used minimal seats,
they seem to run forever, I have a 50 year old car with original seats
and I expect they will still be in place in another 50 years. I think
many problems start when work is accomplished in a marginal fashion
somewhere in its history, rather than being a design flaw. Mark Durham

Sent from my Windows Phone
From: jvhroberts at aol.com
Sent: 5/8/2012 16:12
To: sheridanma1966 at gmail.com; virtualvairs at corvair.org
Subject: Re: <VV> More on valve seat failures

 Well, in part, Marc. The other economy at work here is the cost to
engineer a good solution, even if it was cheap to produce.

Aircraft engines use alloys other than simple steel for the intake
seats, and as I recall, it's a high manganese alloy. The CTE is
actually not much different than aluminum. Also, aircraft valve seats
are much thicker wall and much deeper than a Corvair, as I sit here
looking at a cracked head from a Pratt and Whitney Wasp radial. Yeah,
my garage has some weird stuff in it. <G>

Now, if GM made the seats at least dimensionally similar to an
aircraft engine's seats, would we have the same problems? Probably
not. Would it cost more to produce? Probably not, although in the 60s,
Detroit was notoriously cheap.

Anyway, aircraft engines are way different beasts in their operation
and use. Other air cooled passenger car engines are more fair
comparisons.



John Roberts




-----Original Message-----
From: Marc Sheridan <sheridanma1966 at gmail.com>
To: Virtual Vairs <virtualvairs at corvair.org>
Sent: Tue, May 8, 2012 5:27 pm
Subject: Re: <VV> More on valve seat failures


I think it all comes down to economy. You do things differently when
building an aircraft engine versus one for an economy car. Years ago I went
to Trusports Indycar shop for an open house. We were told how valve seats
were done in the race engines. The exotic alloy seats were left in liquid
nitrogen, while the heads were heated in an oven. With the two temperature
extremes, the seats simply fell  into place. Once temperatures equalized,
the engine builder told us nothing would get them out. Not even a heavy
crash that ripped apart the engine.

A race engine isn't an aircraft engine, but I imagine they do something
similar.

Marc Sheridan


On Tue, May 8, 2012 at 4:23 PM, Kerwin Nailor <kerwinnailor at verizon.net>wrote:

> How do the air cooled aviation engines, flat and radial, deal with keeping
> seats in place? They get some pretty dramatic changes in temp, like heavy
> rain.
>
>
> Kerwin Nailor
> kerwinnailor at verizon.net
>
>
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