As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON DEPARTURE FROM KBFL, THE LEFT ENGINE LOST POWER SHORTLY AFTER TAKEOFF, THE ENGINE RETAINED PARTIAL POWER AND THE PROPELLER WAS NOT FEATHERED. THE PILOT IMMEDIATELY RETURNED TO KBFL. INSPECTION OF THE ENGINE REVEALED A LARGE HOLE THROUGH THE TOP OF BOTH HALVES OF THE ENGINE CASE, WITH CYLINDER #3 PISTON ROD AND PISTON PIN OUTSIDE OF THE CASE AND A COUNTERWEIGHT BROKEN FROM ITS POSITION AND LAYING ON TOP OF A CYLINDER.