Because of the nature of the job and the need for particular tools and equipment, the procedure of resizing the valves, valve seats, and valve guides better known as the valve job is better to be done by skilled personnel. A home mechanic may take off the head, cleanup and perform preliminary inspection and then reinstall the head for it to be taken to the dealer service department or automotive machine shop for the actual service. Carrying out the exercise enable one to know the condition of the head and valvetrain parts and new works and parts required when liaising with an automotive machine shop. It is the dealer service department or automotive machine shop which will be involved in valve and spring removal, with possible reconditioning or replacement, the checking and replacement of valve spring rotators, spring retainers, keepers and checking and replacement of valve seals too, reassembly of the valve components, and ensuring that the correct height of installed spring is attained. Also, the surface of cylinder head gasket will be machined if it is found to be warped. After valve job has been done in the head, the head will be in the 'as new' condition and it is necessary to clean it again before it is placed on the engine to remove metal fragments and abrasive particles that may be remaining in the head from the valve service or the head machining. Compressed air must be used for blowing out all oil holes as well as passages.