Mainly the stems wear. OEM and premium valves were usually chrome plated. You can polish the stems and the non combustion chamber side of the valve with a drill press, wd-40, and 600 wet or dry sandpaper. There is thickness limit on the margin of the valve also. As long as the stems are within spec and you can get a good face with enough margin left, the valve should be good to go.
So if I'm within a half thou on the valve diameter after polishing then I should be good to keep these valves? And for margin limit, you mean the amount of material you can take off the chromed surface?
