As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STUD PULLED OUT OF TACH DRIVE HOUSING COVER ALLOWING OIL TO LEAK OUT ONTO EXHAUST CAUSING SMOKE AND THE FLIGHT TO RETURN TO THE AIRPORT IMMEDIATELY AFTER TAKEOFF. THE THREADS WERE PULLED OUT POSSIBLY FROM REPETITIVELY REMOVING BRACKET FROM THE Y PIPE DURING THE INSPECTION.