What was found
(CAN) DURING A FLIGHT IN THE R44 HELICOPTER, THE PILOT NOTICED A SIGNIFICANT VIBRATION APPROX. 2 HOURS INTO THE FLIGHT. THE VIBRATION LASTED 45 SECONDS. THERE WERE NO AUDIBLE ALARMS & ALL GAUGES READ NORMAL. THE A/C WAS DESCENDING WITHOUT CONTOL INPUTS,AFTER THE 45 SECOND VIBRATION SUBSIDED.A/C RETURNED TO BASE. THE A/C WAS STARTED THE FOLLOWING DAY THE VIBRATION WAS NOTED @102% IN HOVER ,A/C LANDED,WAS SHUT DOWN AND SB388C(VALVE CLEARANCE CHECK) WAS CARRIED OUT.NUMBER 3 AND NR 6 EXHUAST VALVES WERE SEIZED WITH BENT PUSH RODS.CYLINDER NUMBER 1, 2,,4 VALVES WERE BELOW THE ALLOWABLE CLEARANCE