B747-400 REJECTS TKOF DUE TO FAILED BEARINGS IN NO 2 ENGINE.

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WE HAD JUST BEGAN OUR TKOF ROLL WITH THE FO FLYING. I HAD TAKEN THE XFER OF THE THROTTLES AND WE WERE AT APPROX 50 KTS WHEN WE HEARD 3 LOUD BANGS COMING FROM THE L SIDE OF THE AIRPLANE. THERE WAS A SLIGHT TURNING OF THE AIRPLANE TO THE L AND I ABORTED THE TKOF. THERE WERE NO OBSERVED ABNORMALITIES FROM THE ENG INSTS AND THE ACFT TAXIED NORMALLY. NO FIRE OR SMOKE WAS OBSERVED FROM OUTSIDE THE ACFT AND EVERYTHING APPEARED NORMALLY FROM THE TWR AND GND PERSONNEL CHKING THE RWY. WE NOTIFIED MAINT AND RETURNED TO THE GATE. MAINT MET THE ACFT AS WELL AS AN O'HARE RWY INSPECTOR. I WAS INFORMED THAT THERE WAS NOTHING ON THE RWY FROM THE GND PERSONNEL. THE MECHS CHKED THE COMPUTER AND FOUND A PROB WITH THE #2 ENG. 1 MECH CAME UP TO THE COCKPIT WITH BEARING PARTS FROM THE #2 ENG TAILPIPE. I WAS INFORMED THAT THE ENG HAD APPROX 20000 HRS ON IT AND HAD BEEN WRITTEN UP AS COMING IN FROM A PREVIOUS FLT WITH EGT SOME 40 DEGS C HIGHER THAN THE OTHER ENGS. WE DEPLANED THE PAX AND PROCEEDED TO ANOTHER GATE AND AIRPLANE.