As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING RUNUP, CREW FOUND THAT THE LEFT ENGINE QUIT WHEN THE LEFT MAGNETO WAS SELECTED. THE MAGNETO WAS REPLACED. THE REMOVED MAGNETO WAS DISASSEMBLED AND INSPECTED. THE PORTION OF THE PRIMARY CONTACT POINTS THAT IS ACTED UPON BY THE CAM WAS FOUND BROKEN FREE OF THE POINTS ASSEMBLY AND WAS FOUND LAYING INSIDE THE MAGNETO CASE. THE FRACTURE EDGE DISPLAYED A COMBINATION OF BRIGHT AND RUSTED METAL. THIS INDICATES THAT THE PART HAD BEEN CRACKED FOR SOME AMOUNT OF TIME BEFORE FAILING COMPLETELY.