If you are familiar with rebuilding Magneto's as we are, during disassembly, this mainshaft bearing always needs to be inspected! Corrosion and or wear in the ball bearing area can lead to total Magneto failure!  Always replace this bearing if it has corrosion, is loose inside or signs of heavy wear. The Magnetic rotor assy needs this bearing to spin true and straight in order to make a good, high magnetic field for good overall spark. This C5949 bearing is an OEM part from FM.