As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT REPORTED A LOSS OF POWER ON THE RT ENGINE AND DECLARED AN EMERGENCY. MAINTENANCE PERFORMED A COMPRESSION CHECK ON THE CYLINDERS AND FOUND ZERO PRESSURE ON (1) OF THE CYLINDERS. UPON REPLACEMENT OF CYLINDER IT WAS FOUND THAT THE PISTON HAD A (HOLE) DOWN THE SIDE OF THE PISTON. REPLACED PISTON AND NO OTHER DEFECTS WERE NOTED.