Valve and Seat Grinding

Important: 

• Reconditioning the valve seats is very important. The seating of the valves must be perfect for the engine to deliver optimum power and performance. Several different types of equipment are available for grinding valve seats.
• Another important factor is the cooling of the valve head. Good contact between the valve and the seat will ensure that heat will be properly dissipated.
• The recommendations of the manufacturer of the equipment should be followed carefully to obtain the proper results. Regardless of what type of equipment is used, it is essential that valve guide bores be free from carbon or dirt to ensure proper centering of the tool pilot in the guide.
• Valves that are pitted must be refaced to the proper angle. Valve stems that show excessive wear, or valves that are warped excessively must be replaced. When a valve head that is warped excessively is refaced, a knife edge may be ground on part or all of the valve head due to the amount of metal that must be removed. Knife edges lead to breakage, burning or pre-ignition due to heat localizing on this knife edge. If the edge of the valve head is less than 1.25 mm (0.05 in) after grinding, replace the valve.
  Fig 1: Inspecting Valves For Damage

  Courtesy of GENERAL MOTORS CORP.
• Several different types of equipment are available for refacing valves. The recommendation of the manufacturer of the equipment should be carefully followed to obtain the proper results.
• DO NOT reface intake valves. Intake valves with excessive wear or damage MUST be replaced.

1. Inspect the valve for the following:
   • Burnt or eroded areas (1)
   • A worn margin (2)
   • A bent stem (3)
   • A worn or scored stem (4)
   • A worn key groove (5)
   • A worn stem tip (6)
2. Inspect the valve face for the following:
   • Worn or no margin (1 or 4)
   • Pitted surfaces (2)
   • Burnt or eroded areas (3)
   Fig 2: Inspecting Valve Face For Damage

   Courtesy of GENERAL MOTORS CORP.
3. Inspect the valve margin.

   The exhaust valve may be refaced if the margin is greater than 1.25 mm (0.05 in) thick before grinding.

4. Reface pitted exhaust valves on a suitable valve refacing machine.
5. Replace the valve if the margin is less than 1.25 mm (0.05 in) thick after grinding.
6. If the valve face has been ground, it may be necessary to shim the valve spring to obtain the proper spring installed height. Refer to CYLINDER HEAD DISASSEMBLE  .
   Fig 3: Inspecting Valve Margin For Damage

   Courtesy of GENERAL MOTORS CORP.
7. Inspect for a loose valve seat (8 or 11) in the cylinder head (1). The valve seat has an interference fit to the cylinder head.
8. Clean the valve guide (6) bores with a suitable tool. Remove all carbon or dirt from the bores.

   The valve guide must be clean for the seat grinding tool to obtain proper results.

9. Grind the valve seat.

   The recommendations of the manufacturer of the equipment should be followed carefully to obtain the proper results. Regardless of what type of equipment is used, it is essential that valve guide bores be free from carbon or dirt to ensure proper centering of the tool pilot in the guide.

10. Inspect the valve seats.
    • The valve seats should be concentric to within 0.05 mm (0.0021 in) total indicator reading.
    • If the valve seat has been ground, it may be necessary to shim the valve spring to attain the proper spring installed height.

      Refer to CYLINDER HEAD DISASSEMBLE  .

    Fig 4: Inspecting Loose Valve Seat In Cylinder Head

    Courtesy of GENERAL MOTORS CORP.