As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAKEOFF, ENGINE EXPERIENCED A PARTIAL POWER LOSS. PILOT REMAINED IN THE PATTERN AND LANDED. SUBSEQUENT INSPECTION BY MAINTENANCE PERSONELL FOUND A CRACK IN THE #4 CYLINDER. INSPECTION AFTER REMOVING THE CYLINDER REVEALED THAT A CRACK EXISTED FROM ONE SPARK PLUG HOLE TO THE OTHER SPARK PLUG HOLE. THE CRACK RAN TANGENT TO THE OUTBOARD EDGE OF THE EXHAUST VALVE SEAT. THE CYLINDER WAS REPLACED WITH A SERVICABLE PART.