What was found
(CAN) DURING CLIMB OUT , THE RIGHT ENGINE STARTED TO RUN ROUGH. THE PILOT FEATHERED THE ENGINE AND RETURNED TO YELLOWKNIFE .MAINTENANCE FOUND 2 CRACKS AT THE EXHAUST PORT OF NR 7 CYLINDER OF THE RT ENGINE. THESE HAD STARTED TO SPREAD AND LIKELY CAUSED THE EXHAUST VALVE TO MALFUNCTION. MAIN OIL SCREEN CHECKED AND SUMP DRAINED, NO CONTAMINATION FOUND. THE CYLINDER WAS REPLACED, ENGINE GROUND RUN AND RETURNED TO SERVICE. (X)