What was found
LEFT EXHAUST STACK CRACKED. ENGINE WAS VIB CHECKED AND FOUND TO BE VIBRATING EXCESSIVELY. UPON FURTHER INSPECTION, UPPER ENGINE MOUNTS APPEARED TO BE LOOSE. NEW HILOCKS WERE INSTALLED ON UPPER ENGINE M0UNTS OF AIRFRAME. ANOTHER VIBRATION TEST WAS PERFORMED AND VIBRATION DROPPED TO AN ACCEPTABLE LEVEL. STACK WAS REPLACED AND AIRCRAFT RELEASED FOR SERVICE. REF: CONTROL NR 98-5-6.