As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
REMOVED ENGINE FOR NORMAL OVERHAUL. REMOVED THERMOSTATIC BYPASS VALVE TO INSTALL IN REPLACEMENT ENGINE. FOUND CRIMP NUT LOOSE. THIS VALVE IS NOT SUBJECT TO THE RECURRING INSPECTION AS SHOWN IN SB518C BECAUSE OF SERIAL NUMBER. SUGGEST ALL VALVES BE INSPECTED AT REGULAR INTERVALS AS SHOWN IN SB518C. REPAIRED VALVE PER SI 1423. CRIMP NUT LOOSE DUE TO POOR DESIGN.