What was found
JUST PRIOR TO V1, FELT MOMENTARY SHIMMY, DURING CLIMB OUT, HEARD & FELT E2 FAN VIBRATION. E2 FAN VIBRATION GAUGE VARIED FROM .4 TO 1.7 WITH & WITHOUT POWER CHANGE. UPON LANDING, FOUND NR 4 MAIN TIRE TREAD HAD SEPARATED DAMAGING FLAP PYLON & DAMAGING E2 FAN BLADES. COMPLIED WITH WORK CARDS 71-001 & 71-002 ENG REMOVAL & INSTALLATION. OPERATIONS CHECKED & LEAK CHECKED SATISFACTORY. R & R NR 4 MLG TIRE ASSEMBLY IAW WORK CARD 32-002. NO DEFECTS NOTED PN 5013641 & SN JUL102333.