The Cold Valve Face of the valve cover assembly can be lapped clean using fine (at least 800 grit) wet and dry sandpaper on a flat surface such as plate glass or a mirror. Very gently work the face in a circular motion on the wet paper. Do not apply any downward pressure on the cover as this will alter the flatness of the surface. The Hot Seat on the slide valve assembly can be lapped clean in a similar way.
To ensure the Cold Valve Face and the Cold Valve Seat can form a seal, a water soluble abrasive such as toothpaste, can be used to very gently work the two parts together.
A mandrel should be used to clean dirt from the Hot Valve Face inside the main valve body. Again toothpaste has sifficient abrasive qualities to effectively clean the Hot Valve Face with the mandrel. No downward pressure should be applied to the mandrel.