As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PILOT RETURNED TO BASE AFTER NOTICING SMOKE FROM LEFT ENGINE SOON AFTER TAKEOFF. MAINTENANCE DISCOVERED LT MAGNETO HAD SEPARATED FROM ENGINE CAUSING OIL LEAK AND SMOKE. REASON FOR MAGNETO SEPARATION IS UNKNOWN. NEW NUTS AND LOCKWASHERS HAD BEEN USED DURING INSTALLATION, AND STUDS ARE IN A GOOD CONDITION.