What was found
DURING CRUISE FLIGHT, ACFT EXPERIENCED A VIBRATION CONSIDERED EXCESSIVE. REDUCED PROPELLER SPEED FROM NORMAL CRUISE SETTING. CLEARED THE VIBRATION FOR A SHORT TIME. ELECTED TO KEEP 1800 RPM SETTING AND AS FLIGHT CONTINUED THE VIBRATION RETURNED. DECLARED AN EMERGENCY. DESTINATION WAS THE CLOSEST AIRPORT AND LANDED WITHOUT INCIDENT. MAINTENANCE PERFORMED EXTERNAL VISUAL INSPECTIONS OF ENGINE, PROPELLER AND ENGINE ACCESSORIES, WITH NO DEFECTS NOTED. PROPELLER WAS DYNAMICALLY BALANCED WITH 28.4 GRAMS OF WEIGHT USED. A TEST FLIGHT WAS PERFORMED AFTER THE PROPELLER WAS BALANCED WITH NO VIBRATION NOTED. NO AD`S APPLY TO THIS PROP.