On Tue, 22 Jul 1997, Peter Ross wrote:
> Thanks Chip for the excellent and trusted treatise of valve geometries
> and the resulting problems. I always learn a lot from what you write.
>
> FWIW to the statisticians, on the Ocean to Ocean 11 years ago using an
> engine with almost all new replaceable parts in my TC, I burned a hole
> in an exhaust valve about 6000 miles into the trip on about day 18. I
> was using standard valves from Abingdon Spares mating with steel inserts
> in an alloy head, the origin of which I didn't know, but I doubt they
> were hardened. We were using only unleaded fuel with an additive of
> various brands thrown in each time. I think one or two other cars did
> the same thing at about the same mileage,
>
> I've had the head off several times since and the exhaust valves are
> always freckled which laps out quite easily. In other words, a
> premature pitting.
>
> Is burning a hole caused by lack of lead, or by pre-ignition creating a
> hot spot?
Most inserts are hardened, so those in your alloy head (Laystall-Lucas?)
probably are.
A hole burned through a valve indicates extreme overheating of the valve,
or a poor-quality valve that was unable to stand up to normal abuse.
What shape was the seat in at the time? A lot of heat transfer from valve
to head occurs via the seat. If the seat is in bad shape, transfer is
partially blocked, so the valve runs hotter than it should.
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