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?
I think they are made of an incompatible steel , which we can get away with because we run big clearances , something I read in a M Pemberton article? certainly a bit too esoteric for me!!. Maybe a touch of castrol R in the tank would cheer both of you up.
Some valves are made of composite materials that do not agree with the Cast Iron guides used in many Norton Twin cylinder heads. The stems pick up lumps from the guides which then jam up the clearances. You get a similar problem with some supposedly Lead Free valve seats welding themselves to the valve heads.
Some poorly manufactured valves have soft collet ends which don't agree with rocker ends bashing them and bell-out over time. Removing them can then become fun and games. Grinding? Bashing? Heating???
Bent valve stems, thanks to pistons getting to know the valve heads too well can also make a removal job less than straight-forward.
Joyful stuff! Anyway - I see a G&S valves mark etched on the side of the end. Their web site has lots of technical stuff. The valve is from RGM I think. It is non-magnetic (which G&S say is correct for exhausts made from '214N'), and since it's by G&S the shiny shank should be hard chrome plate suitable for use with cast iron guides. So if its material is compatible, that leaves clearances to tight (I think). I just hope they've worn themselves clear now - it's been in for maybe 10,000 miles by now. I'll rub it with moly grease when I reassemble. I'm not changing it. Only one of the pair has the marks - which I suppose suggests it's more likely to be clearance a bit snug otherwise both would be marked.