Thanks for the info Scott. I guess coking isn't the proper term since coke comes from coal but that's what I've heard it called when oil gets turned to pure carbon on a hot engine part. Maybe we should call it "cooking" instead! Anyway the reason I asked is because I had an old four stroke dirt bike once that had that type of valve face pitting and I always suspected leaking valve seals was the cause. It was a "second string" bike that I kept after getting a new one because I wanted something to plod around on that I wouldn't feel guilty not washing after every ride. It smoked for a minute or two after cold starts but then cleared up and ran just fine so I didn't want to take time to install new valve seals. Then it lost compression. Not completely but enough that it was down on power and hard to start. The valves had always been adjusted - if anything a little on the loose side. As they say a ticking valve is a happy valve. It had rockers. I don't think they say that anymore now that shims are so prevalent. But anyway when I pulled the head, inverted it and poured some gas in it, it came out the exhaust port in a matter of seconds. Aha! Leaking exhaust valves. When I removed the valves I discovered that they were being held slightly open by baked-on carbon. It wasn't the nice, even, fluffy coating you'd get with running rich though - it was in one area and hard and crusty - took a knife and a Dremel with wire brush to get it off. My hypothesis at the time was that oil from the leaky valve guide seal was running down and pooling up in the same place every time I parked the bike and then cooking on the valve when I fired it up. Most of the leaked oil went out the pipe as a blue hydrocarbon haze but some stayed on the valve and cooked. The cooked carbon layer just got thicker until it finally interfered with the face/seat seal causing a slight leak - and a hot valve - because as you said the valve depends on conduction for cooling and there's not much conduction going on if the valve and seat aren't touching. So then I had overheated, leaking valves - and that's probably when the pitting started. My valve faces looked exactly like FuddyMucker's. Didn't replace 'em though - there was plenty of margin left so I just lapped 'em and slapped 'em back in there. Definitely replaced the seals though...

Figured it was probably a lash issue but now you know why I was wondering about valve guide seals and coked oil.

Those pictures sure make me want to check valve clearance! Guess I can add that to the list of things to do at 100K miles - which is looming - less than 500 miles away now..

OK that's my long-winded, thread jacking post for tonight.