As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING A ROUTINE INSPECTION, A CRACK WAS SEEN AT THE LOWER SPARK PLUG HOLE OF THE NR 4 CYLINDER. AFTER THE CYLINDER WAS REMOVED, THE CRACK COULD BE SEEN IN THE INSIDE OF CYLINDER HEAD TO ONE SIDE OF THE LOWER SPARK PLUG HOLE. THE CYLINDER SHOWED NO INDICATION OF DISCOLORING OR ANYTHING THAT WOULD INDICATE IT WAS EXPOSED TO EXTREME HEAT.