As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKE OFF, FLIGHT CREW REPORTED LOSS OF 200 RPM AND AN ENGINE VIBRATION, FLIGHT CREW RETURNED AND LANDED IMMEDIATELY. PERFORMED DIFFERENTIAL CYLINDER LEAK CHECK AND DISCOVERED CYLINDER NR 4 HAD A STUCK AND LEAKING EXHAUST VALVE. ENGINE TOTAL TIME 629.6.