My understanding is that burnt valves are moistly caused by tappet
clearances closing up (which they do through normal use as the valves
recess into the head).
This means the seat sealing becomes poor and directly burning
mixture passes through the valve/seat gap, eroding the valve away.
The seat would be less susceptible because of the far great thermal
mass of the head.
This is just my personal understanding, it may not be the correct
reason - perhaps someone can confirm/deny?
Mike
-----Original Message-----
From: andy webster <trunkie@hotmail.com>
To: mgrazian@ltcm.com <mgrazian@ltcm.com>; spridgets@autox.team.net
<spridgets@autox.team.net>
Date: Thursday, 6 May 1999 1:11
Subject: Re:Valve definition
>Michael,
>A lean mixture burns hotter than a rich one, and also a rich mix serves to
>"quench" the combustion chamber ,cooling it slightly.
>A lean mix passes less lead or to be precise tetra-ethyl lead through the
>chambers. Tetra ethyl lead combusts and leaves a protective layer of lead
>oxide on the valves and seats.
>A burned valve, the ones I've seen at least, have been partly eroded
>by hot gases blowing by. I've been told it can even be caused by a
>cracked/leaky exhaust manifold.
>Not sure how to determine one other than pulling the head, but I always
find
>that kind of theraputic.
>ANDY
>
>>From: Michael Graziano <mgrazian@ltcm.com>
>>Reply-To: Michael Graziano <mgrazian@ltcm.com>
>>To: "Spridgets (E-mail)" <spridgets@autox.team.net>, "MGList
>>(E-mail)" <mgs@autox.team.net>
>>Subject: Midget Sway Bar Locator Pairs?, and Valve definition
>>Date: Wed, 5 May 1999 10:44:10 -0400
>>
>>Hey folks.
>>
>>Didn't have time to recheck that compression last night. In fact, I'm
>>pretty busy till next weekend :(. Wedding this weekend :).
>>
>>BUT, Can you believe, I still have questions!
>>
>>1: I'm replacing the bushings on the front sway bar and noticed that the
>>two locators (stops) had different distances between them and the
bushings.
>>The passenger side had 1/2 inch and the driver had 7/8". And they were
>>positioned between the bushings vs the ouside as in Moss' catalog. What
is
>>the correct distance, and should they be affixed on the inside, outside,
or
>>it doesn't matter? And the replacements are the Prothane Poly with that
>>lubricant. Does the lubricant go inside the center whole of the bushing
>>only, or all around them (inside and between the outside and the mounts)?
>>The rubber inside the balls on both links looks pretty dry as well.
Should
>>I replace those?
>>
>>2: What do they mean by a "burnt" valve? Are pieces of it melted? Or is
>>there simply a layer of caked on goop that interferes with the closing of
>>the valve. And why would a lean mixture cause this? How can you tell if
a
>>valve is burnt without pulling the head?
>>
>>and 3: The Lower Prothane bushings package reads Midget till '74. I
>>didn't
>>think there was a difference from the '74 to the '78. Is there a
>>compatibility problem? Planning on getting these done next weekend.
>>
>>Oh so many questions......
>>
>>
>>Michael
>>'78 Midget 1500
>> _____________________________________
>> / \
>>| Michael Graziano |
>>| Long Term Capital Management L.P. |
>>| Phone: 203-552-5706 |
>>| Fax: 203-553-5869 |
>>| Email: mgrazian@ltcm.com |
>> \_____________________________________/
>>
>
>
>
|