All Heads are cleaned in our Cuda hot tank, or normal parts cleaner, disassembled and then sent into our ultrasonic cleaner for a good clean. The heads/parts are then checked. Valve guides are drilled and pressed out and replaced with a much more modern manganese-bronze material, followed by a precise sizing.  The valve seats are then cut to spec. Then the valves get checked and ground. Sometimes it is best to replace the valves if too worn with an oversize valve.