KIPS main valve extends into cylinder

[Dave B]

Tore down my 220 for a fresh top end and removed the KIPS valves for cleaning. After reassembling the exhaust valves I noticed that when I turn the main shaft all the way (counter clockwise) and the main valve is down, it slightly enters the cylinder bore. Has anyone experienced this? I slid the piston with rings on it down the bore while holding the shaft all the way counter clockwise and the rings will catch on the valve. I can't see where the valves can be installed incorrectly for this to happen. Standard bore piston, ring end gap is within tolerance, plating looks good...wouldn't think the bore could be wore beyond the point where it would protrude. It couldn't have done this before tear down or the old piston rings would have snagged the valve...unless carbon build up prevented it from extending fully? Any thoughts??