As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING START-UP OF THE ENGINE, THE NR 1 CYLINDER TRAILING COUNTER WEIGHT ON THE CRANKSHAFT CAME LOOSE FROM CRANKSHAFT AND MADE A HOLE IN THE TOP OF THE CASE. CSB99-3A HAD BEEN COMPLETED 1.7 HOURS PRIOR. REASON FOR FAILURE UNKNOWN AT THIS TIME.