What was found
PROPELLER WAS BALANCED IN PLACE. 10 FLIGHT HOURS LATER, IN CRUISE OVER WYOMING EN ROUTE TO OSHKOSH, SIGNIFICANT VIBRATION OCCURRED, CAUSING DIVERSION TO THE NEAREST AIRPORT. UPON LANDING, BYSTANDERS RAN TOWARD THE AIRPLANE TO EFFECT RESCUE, ASSUMING THE AIRPLANE TO BE ON FIRE FROM THE LARGE CLOUDS OF SMOKE. BALANCE WEIGHTS HAD BEEN ATTACHED BY SCREW RADIALLY INSIDE THE SPINNER BACKING PLATE. THE WEIGHTS (THREE WASHERS ON ONE SCREW) HAD PULLED THROUGH THE ALUMINUM OF THE BACKING PLATE, AND THE RESULTANT PROJECTION DAMAGED THE COWL MOUNT SYSTEM AND COWLING, AS WELL AS THE BACKING PLATE, AND SEPARATION OF THE BALANCE WEIGHTS. THE IMBALANCE CREATED BY THIS TEARING OF THE BACKING PLATE CAUSED SEVERE VIBRATION,