As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
NR 5 CYLINDER WAS REMOVED FROM RIGHT ENGINE AFTER ROUGH OPERATION AT GROUND RUN UP AND COMPRESSION LOSS. INSPECTION REVEALED BENT I BEAM SECTION OF CONNECTING ROD AND DAMAGE TO SKIRT OF PISTON. FAILURE ANALYSIS DETERMINED CAUSE TO BE HYDROSTATIC LOCK DUE TO OVERPRIMING AT STARTUP. NR 5 CYL OF RT ENGINE, NR 6 CYL OF LT ENGINE ARE MOST LIKELY TO HAVE THIS PROBLEM. INDUCTION SYSTEM BALANCE TUBE NEEDS PROPERLY POSITIONED DRAIN FOR LT AND RT TO PREVENT THIS PROBLEM.