As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN)SHORTLY AFTER TAKEOFF THE #1 ENGINE BACKFIRED AND RAN ROUGH. AIRCRAFT RETURNED AND LANDED. MAINTENANCE FOUND LEFT HAND MAGNETO DEAD. INVESTIGATION REVEALED THAT THE PHENOLIC CAM DRIVE GEAR HAD ALL THE TEETH STRIPPED BY THE STEEL GEAR IT MESHES WITH. CAUSE COULD NOT BE DETERMINED AS SHAFT AND GEAR TURN FREELY.