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Valve Seat

  1. Check the valve seat for damage and deformation.
  2. Check the seating width and seating position between valve and valve seat for the intake valve seat and exhaust valve seat.
    1. Clean the valve and valve seat.
    2. Coat the stem (A) of the valve lightly with engine oil and apply red dye evenly on the valve face (B).
      Fig 1: Identifying Valve Stem And Valve Face
      G08317125Courtesy of SUBARU OF AMERICA, INC.
    3. Using the valve lapper, slowly insert the valve with red dye applied into the valve guide. Lightly press the valve against the valve seat without turning the valve, and then slowly pull out the valve.
    4. Check the seating width "W" of valve seat as shown in the figure, using a caliper gauge. Check the seating width "W" between valve and valve seat by measuring the width of red dye on the seating surface of valve seat. If the seating width "W" between valve and valve seat is out of the standard, correct the seating surface of valve seat using the valve seat cutter. For correcting procedures of the valve seat seating surface, refer to step  3).
      NOTE:
      • When the red dye does not appear seamlessly on the valve seat seating surface, lap the valve. For lapping procedure, refer to step  4).
      • When the red dye does not appear seamlessly on the valve seat seating surface even after lapping the valve, correct the valve seat seating surface using the valve seat cutter. For correcting procedures of the valve seat seating surface, refer to step  3).

      Seating width W between valve and valve seat: 

      Intake 

      Standard 

      0.8 - 1.6 mm (0.031 - 0.063 in) 

      Exhaust 

      Standard 

      1.1 - 1.7 mm (0.043 - 0.067 in) 

      Fig 2: Identifying Seating Width Between Valve And Valve Seat
      G08548014Courtesy of SUBARU OF AMERICA, INC.
    5. Wipe off the red dye on the valve and valve seat completely.
    6. Coat the stem (A) of the valve lightly with engine oil and apply red dye evenly on the seating surface (B) between valve and valve seat.
      Fig 3: Identifying Valve Stem And Valve Seat
      G08317127Courtesy of SUBARU OF AMERICA, INC.
    7. Using the valve lapper, slowly insert the valve into the valve guide. Lightly press the valve against the valve seat without turning the valve, and then slowly pull out the valve.
    8. Check the seating position between valve and valve seat. Check the seating position between valve and valve seat by checking the position of red dye on the valve face. If the seating position between valve and valve seat is not at the center of valve face, correct the seating surface of valve seat using the valve seat cutter. For correcting procedures of the valve seat seating surface, refer to step  3).

      Seating position between valve and valve seat: 

      Valve face center 

      Fig 4: Identifying Seating Position Between Valve And Valve Seat
      G08317128Courtesy of SUBARU OF AMERICA, INC.
    9. After inspection, wipe off the red dye completely.
  3. When correcting the seating surfaces of valve seat
    1. Correct the seating angle between valve and valve seat using the 45° valve seat cuter.
      NOTE:
      • Select the size of the valve seat cutter by referring to the outer diameters of the intake valve and exhaust valve.

      Valve outer diameter: 

      Intake 

      Standard 

      33.9 - 34.1 mm (1.335 - 1.343 in) 

      Exhaust 

      Standard 

      27.9 - 28.1 mm (1.098 - 1.106 in) 

      • Grind the seating surface so that the seating width between valve and valve seat becomes slightly larger than the standard value.
      • Gradually reduce pressure at the end of grinding process in order to avoid creating a gap on the valve seat correcting surface.

      Seating angle between valve and valve seat: 

      45° 

      Fig 5: Grinding Seating Surface Width Between Valve And Valve Seat
      G08548017Courtesy of SUBARU OF AMERICA, INC.
    2. Lap the valve. For lapping procedure of the valve, refer to step  4).
    3. Check the seating position between valve and valve seat. For inspection of the seating position between valve and valve seat, refer to step  2).
      NOTE: This procedure is necessary to select a seat cutter to be used in step (4).
    4. Using the 30°, 75° (IN) or 60° (EX) seat cutter, correct the valve seat so that the seating width between valve and valve seat becomes the standard value.
      NOTE:
      • Select a proper valve seat cutter according to the following table.
      Seating position between valve and valve seat Seat cutter selection
      G08548018
      		 When the seating position of valve face is high, grind the surface using the 30° seat cutter until seating width between valve and valve seat becomes the standard value.
      G08548019
      		 When the seating position of valve face is low, grind the surface using the 75° (IN) or 60° (EX) seat cutter until seating width between valve and valve seat becomes the standard value.
      G08548020
      		 When the seating position of valve face is at center, grind the surface evenly using the 30°, 75° (IN) or 60° (EX) seat cutters until seating width between valve and valve seat becomes the standard value.
      • Gradually reduce pressure at the end of grinding process in order to avoid creating a gap on the valve seat correcting surface.
        Fig 6: Creating Gap On Valve Seat Correcting Surface
        G08317133Courtesy of SUBARU OF AMERICA, INC.
    5. Lap the valve. For lapping procedure of the valve, refer to step 4).
  4. When lapping the valve
    1. Coat the stem (A) of the valve lightly with engine oil and put a small amount of valve compound evenly on the valve face (B).
      NOTE:
      • Be careful not to put the valve compound more than necessary.
      • To avoid damaging the valve guide and valve stem, be careful not to let the valve compound contact the valve stem.
        Fig 7: Identifying Valve Stem And Valve Face
        G08317125Courtesy of SUBARU OF AMERICA, INC.
    2. Using the valve lapper, slowly insert the valve with the valve compound applied into the valve guide, and lap the seating surface between valve and valve seat. First, lift the valve and strike it against the valve seat twice, and then slightly turn the valve once. Repeat these steps as one set.
      NOTE:
      • To prevent the seating width between valve and valve seat from exceeding the standard value, be careful not to keep turning the valve while pressing it against the valve seat during lapping.
      • Be careful not to lift the valve too far during lapping in order to prevent the valve from coming off the valve guide.
    3. Wipe off the valve compound on the valve and valve seat completely after lapping.
      NOTE: Be careful not to leave any valve compound in order to avoid malfunction.
    4. Check the seating width and seating position between valve and valve seat.
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