1984 Official Honda TRX200 Shop Manual, Page 70Get this manual
CYLINDER HEADVALVES
VALVE SEAT INSPECTION REFACING
Clean the intake and exhaust valves thoroughly to remove carbon depositsApply Iight coating of Prussian Blue to each va lve seatLap each valve and seat using rubber hose or other handlapping too lRemove the inspect each valveMeasure the width of the valve face SERVICE LIMIT: 2.0 mm (0.08 in)
CAUTION:
The vah'e cannor be groundIf the valve face is burned or badly worn or if it contacts (he seat unevenlyreplace rhe valveInspect each valve seatI'f the seat is too wide, too narrow, or has low spots, the seat must be refinished to seal properly