As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) DURING CLIMB OUT WITH GLIDER IN TOW, THE PILOT REPORTED AN ENGINE VIBRATION. THEY IMMEDIATELY INSTRUCTED THE GLIDER TO RELEASE AND THEN PREFORMED A DOWN WIND LANDING AND RETURN TO HANGER. UPON SHUTDOWN AND INSP IT WAS FOUND THAT CYL NR1 HEAD HAD CRACKED AND SEPARATED FROM THE REMAINDER OF THE CYL.