As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT DEPARTED AIRPORT AND ENGINE BEGAN RUNNING VERY ROUGH. AIRCRAFT RETURNED TO THE AIRPORT (UNABLE TO MAINTAIN POWER OR ALTITUDE). MAINTENANCE FOUND NR 4 CYLINDER HAD BROKEN AND BENT PUSHRODS. THE EXHAUST VALVE PUSHROD WAS FOUND BROKEN FOR ABOUT 8 INCHES IN LENGTH. FURTHER INVESTIGATION REVEALED A BENT PUSHROD IN NR 2 CYLINDER. SUSPECT STUCK/ STICKING VALVES CAUSED FAILURE. ALL CYLINDERS WERE INSTALLED FACTORY NEW AT ENGINE OVERHAUL.