On Tue, 11 Dec 2007 01:55:38 +0000, Scott
wrote:

FOUL!! 100LL has 4 times the lead content than the old 80 avgas and a
LOT more than unleaded auto! Therefore, the 100 octane valves should be
supper lubricated! But, in fact, the 80 octane valve tend to stick if
much 100LL is run through them...

So, somebody answer my question...what is special about 100 octane
valves? The ones I put in my A-65 were Stellite. What does Stellite
do? What about sodium filled valves? What's their claim to fame??

Scott

The 100 octane valves will have different valve stem design (and
likely clearances) and will (from what I've read on the subject) be
designed to run HOTTER to keep the TEL from building up on the tulip
portion and the neck of the valve. This is what causes the "morning
sickness" referred to as hanging valves - otherwise known as "lead
poisoning". Aggressive leaning at less than peak power will also help
reduce this lead build-up.

Stellite can stand a LOT more heat. Sodium cooled valves have liquid
sodium inside the stem and head to act like a "heat pipe" and suck the
heat down the stem to transfer the heat more efficiently to the head.
This would cause the stem area to run hotter, possibly explaining
their use in 100ll conversion valves?

Matt Whiting wrote:
Scott wrote:

Like I said, MIGHT OK, if there is no difference in heat, what are
the 100 octane valves in my A-65 for? Or more generally, why do they
sell 100 octane valves for A-65s and C-85s, etc. that were certified
on 80 octane??? Like I said, I use them, I don't wrench on 'em


Because valves that were designed to be lubricated by the lead in leaded
fuel may not last long when using fuel with no or less lead.

Matt


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