What was found
(CAN)PILOT REPORTED SMOKE IN COCKPIT AND A BIT OF OIL ON THE WINDSHIELD. AIRCRAFT RETURNED TO POINT OF DEPARTURE. POST FLIGHT INSPECTION FOUND #8 CYLINDER PISTON CRACKED AND PISTON RING BROKEN. THE PISTON WAS CRACKED FROM THE PISTON PIN HOLE TO OVER THE TOP OF THE PISTON WITH A SMALL PIECE OF THE PISTON MISSING. NEW PISTON AND RINGS INSTALLED. OIL SCREENS AND SUMP CHECKED SERVICEABLE AND AIRCRAFT RETURNED TO SERVICE.