As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
IT APPEARS THE PISTON PIN BROKE AND THE PISTON HIT THE CRANKSHAFT COUNTERWEIGHT WHICH BROKE A LARGE HOLE IN THE TOP OF THE CRANKCASE. THE AIRCRAFT WAS ON A CROSS-COUNTRY FLIGHT AT NORMAL CRUISE. WHEN THE VIBRATION STARTED, THE PILOT REDUCED POWER, BUT THE VIBRATION CONTINUED SO THE PROPELLER WAS FEATHERED AND FLIGHT CONTINUED WITH REAR ENGINE OPERATING.