On Dec 11, 6:57 am, "RST Engineering" wrote:

The different seat angle is an attempt to "get the lead out" of unburned
tetraethyl lead. Even so, the low temperatures encountered in a low
compression engine lets the lead coagulate on the first cool surface it
finds. That happens to be the valve stem. Therefore, the valve stems are
ever so slightly reduced (.005" comes to mind) so that the lead can plate
out on the valve stem and still not cause the stem to stick on the guide so
often. "So often" is the operative term here. 100 octane will cause valve
sticking, but with the 100 octane valves, just not quite as soon.

Jim

That lines up with what we used to experience with the small
Continentals. The valves tended to stick if the stem/guide clearances
were set at the minimum spec. The other problem with many small
engines is their mixtu the Stromberg carb either had no mixture
control, or it was safety-wired at full rich. So the engine gets too
much fuel, which was OK when 80/87 was available, but it's not OK with
100LL which has four times the TEL spec. My A-65 runs much leaner and
the valves don't get fouled up.

Dan