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Valve Seat Reconditioning

  1. Inspect the valve stem-to-guide clearance (see VALVE STEM-TO-GUIDE CLEARANCE INSPECTION ). If the valve guides are worn, replace them (see VALVE GUIDE REPLACEMENT ) before cutting the valve seats.
  2. Renew the valve seats in the cylinder head using a valve seat cutter.
    Fig 1: Replacing Valve Seats
    G08091931Courtesy of AMERICAN HONDA MOTOR CO., INC.
  3. Carefully cut a 45° seat, removing only enough material to ensure a smooth and concentric seat.
  4. Bevel the upper and lower edges at the angles shown the illustration. Check the width of the seat and adjust accordingly.
    Fig 2: Identifying Seal Upper And Lower Edges Angles
    G08091932Courtesy of AMERICAN HONDA MOTOR CO., INC.
  5. Make one more very light passes with the 45° cutter to remove any possible burrs caused by the other cutters.

    Valve Seat Width 

    Intake: 

    Standard (New): 0.850-1.150 mm (0.03346-0.04528 in) 

    Service Limit: 1.80 mm (0.0709 in) 

    Exhaust: 

    Standard (New): 1.250-1.550 mm (0.04921-0.06102 in) 

    Service Limit: 2.00 mm (0.0787 in) 

  6. After resurfacing the seat, inspect for even valve seating: Apply Prussian Blue compound (A) to the valve face. Insert the valve in its original location in the head, then lift it and snap it closed against the seat several times.
    Fig 3: Identifying Actual Valve Seating Surface
    G08091933Courtesy of AMERICAN HONDA MOTOR CO., INC.
  7. The actual valve seating surface (B), as shown by the blue compound, should be centered on the seat:
    • If it is too high (closer to the valve stem), you must make a second cut with the 60° cutter to move it down, then one more cut with the 45° cutter to restore seat width.
    • If it is too low (close to the valve edge), you must make a second cut with the 30° cutter to move it up, then make one more cut with the 45° cutter to restore seat width.
    NOTE: The final cut should always be made with the 45° cutter.
  8. Insert the intake and exhaust valves in the head, and measure the valve stem installed height (A).

    Intake Valve Stem Installed Height 

    Standard (New): 47.4-47.8 mm (1.866-1.882 in) 

    Service Limit: 48.1 mm (1.894 in) 

    Exhaust Valve Stem Installed Height 

    Standard (New): 47.3-47.7 mm (1.862-1.878 in) 

    Service Limit: 48.0 mm (1.890 in) 

    Fig 4: Identifying Valve Stem Installed Height
    G08091934Courtesy of AMERICAN HONDA MOTOR CO., INC.
  9. If valve stem installed height is over the service limit, replace the valve and recheck. If it is still over the service limit, replace the cylinder head; the valve seat in the head is too deep.
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