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Home >> Acura >> 2003 >> MDX Base >> Repair and Diagnosis >> Engine Mechanical >> Mechanical >> Cylinder Head >> Valve Seat Reconditioning

Valve Seat Reconditioning

  1. Inspect 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: Renewing Valve Seats In Cylinder Head Using Valve Seat Cutter
    G03639403Courtesy 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 edge of the seat with the 30° cutter and the lower edge of the seat with the 67.5° cutter (intake seat) or the 60° cutter (exhaust seat). Check the width of the seat and adjust accordingly.
    Fig 2: Checking And Adjusting Width Of Seat
    G03639404Courtesy of AMERICAN HONDA MOTOR CO., INC.
  5. Make one more very light pass with the 45° cutter to remove any possible burrs caused by the other cutters.

    Valve Seat Width 

    • Standard (New): 1.25-1.55 mm (0.049-0.061 in.) 
    • Service Limit: 2.00 mm (0.079 in.) 
  6. After resurfacing the seat, inspect it 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: Applying Prussian Blue Compound to Valve Face
    G03639405Courtesy of AMERICAN HONDA MOTOR CO., INC.
  7. The actual valve seating surface (B), as shown in Fig 3 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 67.5° cutter (intake seat) or the 60° cutter (exhaust seat) to move it down, then one more cut with the 45° cutter to restore seat width.
    • If it is too low (closer to the valve edge), you must make a second cut with the 30° cutter to move it up, then 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): 46.75-47.55 mm (1.841-1.872 in.) 
    • Service Limit: 47.80 mm (1.882 in.) 

    Exhaust Valve Stem Installed Height 

    • Standard (New): 46.68-47.48 mm (1.838-1.869 in.) 
    • Service Limit: 47.73 mm (1.879 in.) 
    Fig 4: Measuring Valve Stem Installed Height
    G03639406Courtesy of AMERICAN HONDA MOTOR CO., INC.
  9. If the 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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