What was found
(CAN) AFTER NOTICING A RAPID INCREASE IN VIBRATION WE TRIED TO DYNAMICALLY BALANCE THE MAIN ROTOR. SINCE WE WERE UNABLE TO BE WITHIN RECEPTACLE LIMITS, WE REMOVED THE MAIN ROTOR HEAD AND ROTOR BLADES FOR FURTHER INSPECTION. WE FOUND THE HUB HOLE ENLARGED, THE JOURNAL BUSHINGS C-106 WERE WORN BEYOND LIMITS, AND THE BEARING C648-1 WAS OVAL IN SHAPE AND COMPLETELY WORN ON ONE SIDE BY APPROXIMATELY 0.200.THE ROTOR HEAD HAS BEEN REMOVED AND SHIPPED TO ROBINSON HELICOPTER CO. FOR OVERHAUL OR PROBABLE REPLACEMENT.THE PROBABLE CAUSE APPEARS TO BE A PREMATURE WEAR WHICH WAS AGGRAVATED WITH SUBSEQUENT FLIGHTS.