Malcolm:
I run seals on the intake because when the intake valve is open, there is
substantial vacuum on the guide/seal. This tends to pull oil down the stem
into the combustion chamber. Conversely,, the exhaust valve is under
pressure when it is open so there is little chance of oil getting into the
combustion chamber from this path. Because less oil goes down the exhaust
valve stem and because it runs drastically hotter than the intake valve many
leave the seals off of the exhaust valves as a safety measure to prevent a
valve sticking in the guide. I had this happen with an XKE on the street
and have been spooked ever since.
Richard, FP sprite/AP corvette.
----- Original Message -----
From: MalcolmCox <malcox@napanet.net>
To: <vintage-race@autox.team.net>
Sent: Saturday, January 29, 2000 11:35 AM
Subject: Valve Stem Seals
> I have a question(s) about valve stem seals.
> My MGA came with teflon seals installed on all 8 valve guides. That head
> sadly now rests in piece(s), so building up a new head is the order of the
> day.
> I had never seen an engine before with stem seals, not having rebuilt an
> engine since 1965!
>
> 1) So why are valve stem seals a good thing, don't the valve guides need
> SOME lubrication?
>
> 2) It has been suggested that they should be fitted only to the inlets,
> since they prevent oil from getting sucked down the stem into the inlet
> port, thereby reducing the effective octane value.
>
> 3) At 11:1 and 110 octane race gas, do I care?
>
> Malcolm Cox, headless in Napa
>
>
>
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