As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR3 CRANKSHAFT ROD FAILED IN FLIGHT - KNOCKING A HOLE IN THE CRANK CASE. ENGINE REMAINED RUNNING AND PILOT WAS ABLE TO RETURN ACFT TO AIRPORT. ONE QUART OF OIL WAS REMAINING IN THE OIL TANK. PERFORMED A TEAR DOWN INSPECTION AND WAS UNABLE TO COME UP WITH A CONCLUSIVE CAUSE FOR THIS ENGINE FAILURE. COPY OF THEIR REPORT ATTACHED.