Go to Sears, or an automotive store like AutoZone, but get a kit to lap your valves. Our you could get a little suction cup (like something used to stick on walls, refrigerators, showers, etc.), and place it on a small straight stick or rod. Then purchase some soft valve grinding compound.
Uniformally place the valve grinding compound around the seating surface of the valve. Place the valve in the head. Using the rod or kit with the suction cup, place it on the valve and rotate it in a rapid fashion, kind of like twisting a stick between your hands trying to start a fire. (By the way, has anyone ever accomplished that?) apply lite to moderate pressure. When the valve grinding compound turns a different shade of gray, probably light gray, pull the valve out of the head, clean off the compound and inspect. You will be able to notice if the grinding compond hasn't affected any areas, indicating the area will not seal.