Because of the extent of its procedure and the miscellaneous instruments and machineries that are essential for it, performing some valve operations that include servicing of the valves, as well as the valve seats, and guides is better implemented by a professional known as a valve job. It is in this way that a home mechanic can remove and disassemble each head, clean and inspect them before reassembling them to be forwarded to the dealer service department or an automotive machine shop for the true valve servicing. The dealer service department or automotive machine shop will have to take out the valves and springs, to recondition or replace the valves and valve seats, they will also have to recondition the valve guides then examine and replace the valve springs, spring retainers or rotators and keepers as required, replace the valve seals with new ones, replace or reinstall the valves and guarantee correct installed spring height. Also, any surface of the cylinder head gasket will be machined where warped. As far as head is concerned once the valve job is done by a professional it will be as good as new can be. These surfaces need another cleaning after its return also to ensure that there are no more tiny metal particles and abrasive grit.Also there would be additional cleaning to this head before using it on the engine so as to get rid of all these particles that were removed during the valve service or head resurfacing. Oil, oil mist galleries or oil paths can be blown through with compressed air; installed spring height is to be checked if correct.