As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE COMPLYING WITH TEXTRON LYCOMING SB 518A, REMOVED THE BYPASS VALVE AND FOUND THE SPRING WHICH MAINTAINS PRESSURE ON THE SEAT BROKEN. PART OF THE SPRING HAD ROTATED AND WAS EXTENDING BEYOND THE VALVE SEAT. FATIGUE SUSPECTED AS CAUSE. RECOMMEND INSPECTING SPRING AS WELL WHEN COMPLYING WITH SB 518A.