As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT TOOK OFF FROM HANSCOM AND LANDED AT NANTUCKET WITHOUT INCIDENT. PILOT GOT BACK INTO AIRCRAFT AND TAXIED TO THE RUNWAY. DURING TAKEOFF ROLL, PILOT HEARD A LOUD KNOCKING SOUND AND ABORTED TAKEOFF AND TAXIED BACK TO HANGAR. AFTER PULLING ALL THE CYLINDERS OFF AND REMOVING ALL CONNECTING RODS, THE NR 4 CONNECTING ROD JOURNAL WAS FOUND CRACKED IN HALF. THE NR 4 CONN ROD WAS HOLDING THE CRANKSHAFT TOGETHER.