As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS IN CRUISE FLIGHT IN BANNER TOW CONFIGURATION. A LOUD AUDITABLE BANG WAS HEARD. ENGINE EXPERIENCED EXTREME VIBRATION FOLLOWED BY TOTAL LOSS OF POWER. PILOT CONDUCTED A FORCED LANDING IN A SOCCER FIELD. UPON ENGINE INSPECTION, #2 CYL. EXPERIENCED EXHAUST VALVE HEAD FAILURE FROM VALVE STEM. THE VALVE HEAD IN TURN PUNCHED A HOLE THRU THE PISTON HEAD. ALUMINUM FLAKES FOUND THROUGH OUT ENGINE, PRESUMABLY FROM PISTON DAMAGE. ENGINE REMOVED FOR REBUILD.