1991 Yamaha Outboard Factory Service Manual 9.9 and 15 HP, Page 109Get this manual
Disassembly 1Using slotted-head screwdriver, remove the clip and then the stopper, spring, pinion and front cover, in that order Inspection and repair Armature 1Check the surfaces of the commutatorUsing sandpaper (#500 or #600), smooth out any rough surfaceIf roughened excessively, turn the commutator in latheIf run-out is 0.2 mm (0.008 in) or more, repeat the same step2Measure the commutator mica under-cutIf the depth is 0.5 mm or less, cut it to the specification0.8 mm (0.02 0.03 Undercut: 0.5 in)