Yamaha 115-225 HP Outboards Service Manual, Page 193Get this manual
PT_T_M_O_T_OR 3) Measure the mica undercuttingIf the undercut is less than the specification, scrape between the segments with hacksaw blade and then carefully remove all particles of metal and mica with compressed airMica undercut: 0.40.8 mm (0.020.03 in)
4) Check the continuity and insulationIf there is open circuit between commutator segments, or there is continuity between segments and the cor, replace the armature complete'_ I1