Since the activity involves precision and the use of specific tools, carrying out the process of repairing valves, valve seats, and valve guides, usually referred to as a valve job, should be left to a professional. A home mechanic can take off and unbolt the head(s) of the engine for preliminary washing and examinations, and then can bring it to a formal dealer or a machine shop for the actual service he/she wants for the head. This inspection enables one to know the status of the head(s) and valvetrain parts so that when consulting an automotive machine shop one is conversant with the required work and new parts. The dealer service department or automotive machine shop will take off the valves and springs, recondition or replace the valves or valve seats, then recondition the valve guides, as well as examine and replace valve springs, spring retainers, and keepers when necessary and replace valve seals, Assemble reconditioned or new valves and verify proper installed spring height. Also, any surface of the cylinder head gasket will be machined if it has been found to be warped. After the valve job, the head(s) will be in essentially as-new shape, and it needs to be cleaned yet again before the heads are bolted to the engine to remove any remaining minute metal chip particles and sharp abrasive grit that may be adhering on the heads from the service or resurfacing work; compressed air should be used to blow out all the oil ways and holes if available.