VALVE GRINDING
To grind a pitted or worn mechanically operated valve, the pressure should be released by compressing the spring and removing the key or other device by which it is held in place. On removing the plug over the valve pocket, the upper surface of the valve disk will be exposed, and it will be found to be provided with a slot. While many grinding pastes may be purchased, good results will be obtained by mixing machine oil with flour of emery until it is thick. Plugging the opening from the valve pocket to the combustion space with cotton waste to prevent the paste from entering the cylinder, spread it on the valve disk and seat, and rotate the disk on its seat with a screwdriver, preferably by means of a bit brace. Every little while the disk should be lifted and replaced on the seat in a new position, in order to distribute the wear evenly, and the grinding continued until a smooth surface shows all around both disk and seat. It is not necessary to smooth the entire surface of the disk and seat, for the pressure will be retained by a narrower surface.
An automatic valve may be removed from the cylinder by unscrewing or unbolting its cage, and after releasing the spring the cage may be held in a vise while the grinding is performed.
After grinding, all traces of the paste should be removed by washing with gasoline, for any particles that remain will cause rapid wear. When replacing the spring, that of the mechanically operated valve will be found difficult to compress to the point at which the key or washer may be slipped into position, and to simplify this many engines are built with a knob or boss on the cylinder to serve as a fulcrum by which a forked lever may be used. If this is not the case, the spring may be sufficiently compressed in a vise, and bound endwise with wire to retain it, the wire being cut when the spring and key are in position.