As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) PILOT REPORTED ENGINE ROUGH AT 80 PERCENT RPM. ACFT WAS GROUNDED AND A COMPRESSION CHECK WAS CONDUCTED. CYLINDER 1 WAS FOUND TO HAVE 58/80 PSI. CYLINDER AND PISTON REMOVED AND COMPRESSION RING WAS FOUND CRACKED. PISTON/CYLINDER REPLACED. ACFT RETURNED TO SERVICE.