[Dave at Pelican Parts]

OK, first to make sure we've got the same picture in our heads: The adjuster is a screw with a rounded end. The rounded end pushes directly on the tip of the valve. (The tip is the part farthest away from the combustion chamber.) When the adjuster pushes on the valve, it pushes against the valve spring and opens the valve.

From there, I think it's not that hard to see how one piece of metal pushing on another piece of metal might wear one or both of them. The problem is probably worse in motors that have sat around for a long time, since there may be very little or no oil on the contact surfaces. The term is "galling", where friction can "rub away" some of the metal.

On the adjusters, this leaves pits and craters. On the valve tips, you will see small smooth depressions in a circle that is partway between the edge and the center. Or the tip can "mushroom" out.

In general, the adjuster and the valve tip have very similar "hardness" characteristics. If they didn't, then one of them would wear out pretty quickly. Some aftermarket SS valves seem to be softer than the stock adjusters, and they tend to "mushroom" pretty quickly.

Hope this helped to clear it up some.

--DD