As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT ENGINE RPM WOULD START CLIMBING AND THE PROP CONTROL HAD NO EFFECT ON REDUCING RPM. DURING TROUBLESHOOTING FOUND THE REAR CRANKSHAFT PLUG HAD COME LOOSE IN THE CRANKSHAFT ALLOWING OIL TO BYPASS BACK TO THE ENGINE SUMP. UNABLE TO DETERMINE THE CAUSE FOR LOOSE PLUG. PLUG REPLACED.