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Cylinder Head Overhaul: Reconditioning

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  1. Valve Seat - Reconditioning
    GHH378245Courtesy of HONDA, U.S.A., INC.
    		 1. Inspect valve stem-to-guide clearance. If the valve guides are worn, replace them before cutting the valve seats.

    2. Renew the valve seats in the cylinder head using a valve seat cutter.

    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 in the illustration. Check the width of the seat and adjust accordingly.

    GHH378246Courtesy of HONDA, U.S.A., 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):  0.85-1.15 mm (0.0335-0.0453 in) 
    Service Limit:  1.60 mm (0.0630 in) 
    Exhaust: 
    Standard (New):  1.25-1.55 mm (0.0492-0.0610 in) 
    Service Limit:  2.00 mm (0.0787 in) 
    GHH378247Courtesy of HONDA, U.S.A., INC.
    		 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.

    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 valve stem installed height (A).

    Intake Valve Stem Installed Height 

    Standard (New):  48.65-49.35 mm (1.9154-1.9429 in) 
    Service Limit:  49.68 mm (1.9559 in) 

    Exhaust Valve Stem Installed Height 

    Standard (New):  44.90-45.60 mm (1.7677-1.7953 in) 
    Service Limit:  45.93 mm (1.8083 in) 
    GHH378248Courtesy of HONDA, U.S.A., 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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