What was found
(CAN) INITIAL PROBLEM ENCOUNTERED WAS A CHANGE IN IDLE SPEED. IDLE WAS ADJUSTED, AIRCRAFT WAS TEST FLOWN & NBO PROBLEMS EXISTED.NEXT DAY AIRCRAFT IDLE SPEED HAD CHANGED. IDLE WAS ADJUSTED & RIGGING CHECKED. AIRCRAFT WAS RUN & TEST FLOWN. WHILE AIRCRAFT WAS RETURNING TO SIGHT IT BEGAN N1 FLUCTUATIONS. THE PILOT LANDED & PULLED COLLECTIVE, FLUCTUATION STOPPED. RETURNED A/C TO A MAINTENANCE FACILITY. AT THIS TIME HE HAD TO REDUCE TO THROTTLE TO PREVENT ENGINE OVERSPEED. FUEL CONTROL WAS REMOVED. UPON REMOVAL A LARGE AMOUNT OF METAL FLAKES FELL FROM THE F.C.U. DRIVE BEARING HAD FAILED & THE SHAFT WAS FREE FLOATING.