As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FOUND 11 OUT OF 12 CYLINDERS WITH THIS P/N PISTON WHICH IS NOT APPROVED FOR USE IN GTSIO520 ENGINES. PISTONS WERE SENT FROM ECI AS PART OF A GTSIO-520 CYLINDER ASSY. P/N 632585 CYLINDER IS DOMED WITH NO STEEL INSERT FOR THE TOP RING GROOVE. THE CORRECT PISTON FOR THE GTSIO520 ENGINE IS FLAT WITH A STEEL INSERT. ONE PISTON WAS CORRECT ON LT ENGINE, BUT THIS WOULD CAUSE AN OUT OF BALANCE CONDITION.