As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CYLINDER HEAD IS CRACKED. THIS IS THE THIRD CYLINDER ON THIS ENGINE THAT THE HEAD HAS DEVELOPED HOLES IN THEM. THE FIRST WENT AT ABOUT 800 HOURS. WE OPERATE THIS ENGINE IN A FLIGHT SCHOOL. HAPPENED UNDER NORMAL FLIGHT OPERATIONS. PROBABLE CAUSE UNKNOWN. RECOMMENDATION TO PREVENT RECURRENCE TO ASCERTAIN THE BATCH OF CYLINDERS MANUFACTURED AT THIS TIME. REMOVE CYLINDERS FROM SERVICE.