2006-2012 Honda TRX90 TRX90EX/X Service Manual, Page 109Get this manual
CYLINDER HEADNALVES VALVE SEAT INSPECTIONREFACING Clean the intake and exhaust valves thoroughly to remove carbon depositsApply light coating of Prussian Blue to the valve seatsLap the valves and seats using rubber hose or other hand-lapping tool
Remove the valve and inspect the valve seat faceThe valve seat contact should be ithin the specified width and even all around the circumference
STANDARD: 1.01.1 mm (0.0390.043 in) SERVICE UMIT: 2.0 mm (0.08 in)
If the seat width is not within specification, reface the valve seat,SEAT WIDTH