Honda Outboards BF40A/BF50A Service Manual, Page 245Get this manual
HONDA BF3EiA-4EiA
bINSPECTION BRUSH LENGTH
Measure the brush lengthIf brush length is less than standard, replace the brush holderSTANDARD 9.8 mm (0.39 in) SERVICE LIMIT
5 mm (0.2 in)
BRUSH INSULATION
Check for continuity between the brushesThere should be no continuity