Looks terrible doesn't it . . .
I think it is created by two primary processes, one being the capture, deposit and crushing of tiny lead deposits and the other is high temperature corrosion. But since the seat is quite a bit cooler than the valve head, lead deposits is the winner.
Seat wear is controlled by the hardness of the materials, so you would not automatically see that. It is likely at WOT your carb is allowing a richer mixture (relatively) to this jug.
You ever find these tiny lead balls in the chamber or stuck in the spark plug?
This process is one reason that you don't want a valve job with those precision three angles and a narrow contact rim for an aircraft engine. At least not one you want to last 2-4000 hrs, it should have a wider contact rim.
Valve faces look considerably different in diesel, or non-leaded gasoline engines for this and other reasons. Longer hours (10,000) on a diesel with a duty cycle of an aircraft will look much smoother, but it too depends on fuel, oils, and operating temperatures.
Last edited by BillL : 09-15-2021 at 05:26 AM.