As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ENGINE RUNNING ROUGH. PERFORMED COLD COMPRESSION CHECK. COMPRESSION WAS ZERO. AIR LOOKING PAST EXHAUST VALVE. REMOVED ROCKER ARM COVER, NOTED EXHAUST VALVE STICKING IN OPEN POSITION. REMOVED CYLINDER. PISTON HAD STRUCK EXHAUST VALVE. REPLACED CYLINDER AND PISTON. PISTON WAS DIFFERENT THAN ORIGINAL PN WAS THE SAME, TOP OF PISTON WAS CONCAVE WHERE AS ORIGINAL PISTON WAS FLAT. (K)