WHILE CUTTING BRACE LOOSE DURING REPAIR PROJECT, GREASE IN BULL GEARBOX WAS IGNITED. BECAUSE OF DIFFICULTY GETTING TO SOURCE OF FIRE, EXTINGUISHERS COULDN'T EXTINGUISH COMPLETE FIRE & FOAM FROM FIRE DEPT UNITS WAS USED. FIRE CONFINED TO GEARBOX INTERIOR. DAMAGE WAS PREDOMINATELY SMOKE & A FEW NEARBY WIRES WERE REPLACED DUE TO HEAT. CLEANUP/REPAIR ADDED UNDER 1/2 DAY TO PROJECT.