I removed my exhaust valves. One of them has signs of surface damage, as if there has been some pick-up of specs of iron or steel. One spot was close to the top if the valve an proud of the surface enough for me to be forced to drift the valve out..not very hard, but worrying.
The valve moved freely over its required range, but there were a few more spots lower down. I wonder why? It cast cast iron guides. They aren't sticking..at least not when cold
I've polished off any lumps, but I wonder why they appeared? Might the stem clearance be smaller when hot?