Date:         Sun, 24 May 2009 11:32:52 -0700
Reply-To:     aatransaxle <daryl@AATRANSAXLE.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         aatransaxle <daryl@AATRANSAXLE.COM>
Subject:      Re: nasty AMC exhaust valve, photos here
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
              reply-type=original

Now mind you this is going way back into my brain...and correct me if I am
wrong of course...
Doesn't the valve transfers it excess heat when its actually closed for that
brief time that it's not open???
When the valve is open, the only way to transfer the heat is thru the valve
stem..
If thats the case, a tight valve never seats onto the valve seat and
crystalizes the stem just below the head.
Thats the way it was taught to me in the early 70's when broken valves were
the norm on aircooled engines...and why we adjusted tham so religiously
every 6000mi
Still happens that way I would think, but not near as much as the
watercooled motors run much cooler head temps.
When overrevving, the valve spends less time "seated" and more time open,
hence less transfer of excess heat. That and when it suddenly starts being
seated and banging on the seat harder, any stresses may make it pop off the
stem.

Daryl of AA Transaxle
(425) 788-4070
aatransaxle.com
86 Syncro Westy
Zetec in the trunk
----- Original Message -----
From: "Doug Noganav" <vanagon@ASTOUND.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Sunday, May 24, 2009 10:01 AM
Subject: Re: nasty AMC exhaust valve, photos here


> Wondering if just before the rpm where the valves actually float,  if the
> "speed" of the valve at high revs increases the inertia and therby the
> degree of impact of the valve hitting the seat?
>
> The greatest load on the valve head is at the highest rpm before the valve
> floats?
>
>
>
>
>
>
> ----- Original Message -----
> From: "pdooley" <psdooley@VERIZON.NET>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Sunday, May 24, 2009 9:22 AM
> Subject: Re: nasty AMC exhaust valve, photos here
>
>
>> The over-rev theory is interesting.
>> If over-revved, the valves will float.
>> What does that do?  Well, the valves don't actually close, so the valves
> are
>> not banging into the seats, and theoretically would endure less stress
> than
>> running at the threshold of float.
>>
>> Now if the float causes mechanical interference, that's another story.
>>
>>
>> -----Original Message-----
>> From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
>> Of
>> Jake de Villiers
>> Sent: Sunday, May 24, 2009 10:34 AM
>> To: vanagon@GERRY.VANAGON.COM
>> Subject: Re: nasty AMC exhaust valve, photos here
>>
>> David
>>
>> Under acceleration, if you bang it into second when you wanted fourth,
>> you
>> WILL over-rev your motor - the limiter has nothing to say about it.  Or
>> coming downhill, say...
>>
>> I remember hitting 6200RPM in fourth in my Twin Cam Fiat and banging it
> into
>> fifth - missed and got third and learned that Fiat rod bolts are good  to
>> ~7500 RPM!
>>
>> That exhaust valve was banged into and broken off so it was in the way
> when
>> the piston was coming back up, so either the keepers let go, the spring
>> broke or the valve was floating...
>>
>>
>>
>> On Sat, May 23, 2009 at 11:46 PM, David Beierl
> <dbeierl@attglobal.net>wrote:
>>
>> > At 02:16 AM 5/24/2009, Scott Daniel - Turbovans wrote:
>> >
>> >> re
>> >> Maybe, or maybe that's what happens when you spin your WBX to 7000 RPM
> on
>> >> a
>> >> missed shift!  =)