What was found
CREW RETURNED ACFT TO THE GATE AFTER ENG NR 1 HUNG START AND AN ABORTED ENG NR 1 HOT START. PASSENGERS WERE DEPLANED. MAINTENANCE DISCOVERED NR 1 ENG SMOKING AND SUSPECTED ENGINE CORE FIRE. MAINTENANCE PROCEEDED WITH NR 1 ENG DRY MOTORING TO EXPEL RESIDUAL FUEL. GROUND CREW REPORTED FLAMES COMING FROM INSIDE THE ENGINE. MAINTENANCE NOTICED SMOKE BECAME PROGRESSIVELY WORSE BUT THERE WAS NO FIRE WARNING INDICATION IN THE COCKPIT. MAINTENANCE DISCHARGED BOTH ENGINE FIRE BOTTLES AND NOTIFIED FIRE DEPARTMENT. FIRE WAS EXTINGUISHED. ENGINE NR 1 WAS REMOVED AND REPLACED. ENGINE LEAK AND OPERATIONAL CHECK WAS PERFORMED AND ACFT WAS APPROVED TO RETURN TO SERVICE.