As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ROTOR CAP ON EXHAUST VALVE BROKE INTO MANY PIECES. VALVE KEEPER CAME OFF AND THE EXHAUST VALVE HIT THE PISTON. ENGINE BECAME VERY ROUGH RUNNING. WE THINK THAT THE LIFTER LOST ITS PRIME AND THERE WAS EXCESSIVE CLEARANCE BETWEEN VALVE AND ROCKER ARM.