As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT ENGINE BEGAN TO RUN ROUGH AND AN INCREASED POWER SETTING WAS REQUIRED TO MAINTAIN LEVEL FLIGHT. THE HELICOPTER IMMEDIATELY RETURNED TO THE HELIPAD AND MADE A NORMAL LANDING. BORE SCOPE INSPECTION REVEALED THAT THE #3 CYLINDER EXHAUST VALVE HAD BROKEN AT THE STEM AND WAS RELEASE INTO THE CYLINDER. SEVERE CYLINDER DAMAGE RESULTED AS WELL AS METAL CONTAMINATION OF THE OIL SYSTEM.