50. Valve Guide Reaming and Valve and Seat Grinding

1. Ream the valve guides for oversize valves if the clearance exceeds the specifications.
2. Ream the valve guide bores for the oversize valves as necessary.
3. Reconditioning the valve seats is very important. Recondition valve seat after reaming the valve guide bores or installing the new valve guides.
^ The valves must seat perfectly for the engine to deliver optimum power and performance.
^ Cooling the valve heads is another important factor. Good contact between each valve and its seat in the cylinder head is necessary to ensure that the heat in the valve head is properly carried away.
^ Regardless of what type of equipment is used, it is essential that the valve guide bores are free from carbon or dirt to ensure the proper centering of the pilot in the guide. The valve seats should be concentric to within 0.05 mm (0.031 inch) total indicator reading.
^ Reface pitted valves on a valve refacing machine in order to ensure the correct relationship between the head and the stem. Replace the valve if the stem is warped, or if the stem shows signs of excessive wear. Replace the valve if the edge of the head is less than 0.79 mm (0.031 inch) thick after grinding.
^ Several different types of equipment are available for reconditioning valves and valve seats. Use the manufacturers recommendations of equipment to attain the proper results.