As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DISCOVERED DURING FINAL TORQUING OF THE MAGNETO HOLD DOWN NUTS, THE IMPULSE COUPLING WOULD BOTTOM OUT IN THE ENGINE GEAR HSG. THIS WOULD LOCK THE COUPLING, CAUSING IT TO NOT WORK. IF THE COUPLING WAS PARTIALLY ENGAGED, IT WOULD HOLD THE DISPLACED TIMING BETWEEN THE IMPULSE COUPLING AND THE MAGNETO.