Mustang GT V8-4.6L SOHC VIN X (1998)
Valve Seat: Service and Repair
CAUTION: The interference angle of the valve and seat should not be lapped out. Remove all grooves or score marks from the end of the valve stem
and chamfer it as necessary. Do not remove more than 0.254 mm (0.010 inch) from the end of the valve stem or excessive valve clearance may occur.
If the valve face runout is excessive and/or to remove pits and grooves, reface the valves to a true 45-degree angle. Remove only enough stock to correct
the runout or to clean up the pits and grooves. If the edge of the valve head is less than 0.794 mm (0.031 inch) thick after grinding, replace the valve
because the valve will run too hot in the engine.
If the valve and/or valve seat has been refaced, check the clearance between the rocker arm pad and the valve stem with the valve train installed in the
engine.
Measure the valve seat width. Reface the valve seats if the width is not within specifications.
Refacing the valve seat should be closely coordinated with the refacing of the valve face so that the finished seat and valve face will be concentric and
the specified interference angle will be maintained. This is important so that the valve and seat will have a compression-tight fit. Make sure refacer
grinding wheels are properly dressed.
Grind the valve seats to a true 45-degree angle. Remove only enough stock to clean up pits and grooves or to correct the valve seat runout. After the seat
has been refaced measure valve seat contact width.
The finished valve seat should contact the approximate center of the valve face. Determine where the valve seat contacts the face.
To do this, coat the seat with Prussian Blue and set the valve in place. Rotate the valve with light pressure. If the Prussian Blue is transferred to the
center of the valve face, the contact is satisfactory. If the Prussian Blue is transferred to the top edge of the valve face lower the valve seat. If the Prussian
Blue is transferred to the bottom edge of the valve face, raise the valve seat.