Re: Burned valve

["Paul Misencik" <paul@domain.elided>]

> Since, I am a digester of this list, I leaned new words like "burned
valve". I
> never worried about that before (Audi and VW ownership) and in fact, to be
> honest, I don't know what it is and what is the cause and symptom.
> Any lister can provide me some explanation or a web site
> I am currently in the process of adjusting my valve clearance on my 86
spider
> and would appreciate to know the technical reason of doing it well.

These two questions are related.  A burned valve is pretty much just what it
sounds like - a valve that has been damaged by extremely high heat.  Since a
valve cools best when it is properly seated, incorrect valve
clearances/adjustment can cause the valve to be exposed to extremes of heat
from combustion.  (It's more common with exhaust valves, because the intake
valve has a cooling intake charge applied to the back of it once every
cycle.)

Eventually, if a valve is misadjusted and continues to be exposed to extreme
heat, it will become damaged, or "burned."  Sometimes it cracks.  Sometimes
it just erodes along large sections of the face.  Sometimes chunks can even
be knocked off it.  Once a valve is burned, its integrity is compromised and
you start to lose compression in the affected cylinder, etc., etc.

It can happen to ANY car.  VW, Audi Alfa... anything.  It's less common on
cars that do not require valve adjustments, but burned valves can sometimes
occur even in a properly maintained car...

Hope that helps.

Paul Misencik
Huntersville, NC  28078
email: paul@domain.elided
www.paoloroman.com
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