. . . or a slight bit of crud on the seat allows combustion through and warps them. Back in Post #4, the engine I was talking about is the one in my mid-`80s Chevy 1-ton pickup. On a 500-mile trip towing a travel trailer, almost all highway, it ran fine the whole way . . . until the last offramp where it was limping on a cylinder. Checked for fouled plugs then limped it back home at the end of the trip. Burned exhaust valve. Part of the valve, where it met the seat, was discolored. Otherwise you couldn't tell it had a geometry issue, unless you put it in a drill press and spin it. Just a tiny little low spot.

Combustion gases are supposed to stay in the chamber during combustion, but if a valve doesn't seat (intake or exhaust), some of that combustion comes through each time and little by little eats at the valve and seat. Little by little but thousands of times a minute.

Would you be able to tell by engine sound that different brand valves have been used? Melling and GM brands used. I may likely to use all Melling for intakes.

No, there'* no way to tell that way. Even if one breaks or doesn't seal or whatever, nobody would be ably to hear those sounds and say "Oh, I hear the unique sound of a Melling exhaust valve on cylinder 2!"