As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING INSPECTION THE #4 CYLINDER OF THE LEFT ENGINE WAS FOUND TO HAVE LOW COMPRESSION. UPON FURTHER INSPECTION THE EXHAUST VALVE HAD FOUR SMALL CHIPS IN THE EDGE OF THE VALVE, AND THE EXHAUST VALVE SPRING HAD PIECES THAT HAD COME APART. NO DAMAGE TO THE ROCKER ARM OR PISTON FACE WAS NOTICED. ADJACENT CYLINDERS (2&6) DID NOT SHOW ANY SIGNS OF DAMAGE.