What was found
UPON COMPLETION OF A 1.7 HR FLT, PILOT NOTICED SHUDDERING VIBRATION AFTER ROLLING THE TWIST GRIP TO IDLE. PILOT REPORTED PROBLEM TO MAINT, INSPECTION REVEALED MOVEMENT BETWEEN T/R G/B AND TAILBOOM CASTING. THREE G/B STUD NUTS WERE FOUND LOOSE, ONE ALIGNMENT PIN LOOSE, ONE MOUNT STUD BROKEN, AND TAILBOOM TO G/B MOUNT HOLES WERE WORN BEYOND LIMITS. NO VISIBLE DAMAGE WAS NOTED ON T/R ASSY. THE TAILBOOM AND G/B WERE REPLACED USING ORIGINAL T/R ASSY. STRONG VIBRATION EMANATING FROM THE T/R WAS FELT DURING GROUND RUN AT IDLE. SERVICEABLE T/R ASSY WAS INSTALLED. GROUND RUN, NML AND T/R WAS BALANCED. ALL PARTS WERE SENT TO MFG FOR EVALUATION.