1990 Johnson Evinrude "ES" 40 thru 55, P/N 507872, Page 253Get this manual
Cleaning and Inspection 1Inspect the brushes; replace if one-half worn, damaged, or crackedReplace brush springs, if weak2Clean commutator with 300 grade emery clothIf commutator surface is unevenly worn or pitted, turn on latheRemove any trace of oil or metal dust from commutator
3 Check the armature on growler for shorted turnsCheck armature for grounding by using test light or meterInspect armature insulation for indications of overheating or damaged windingsClean off any deposits of carbon or foreign matter which may contribute to later failure of the windings
4 Check permanent magnetsMagnets should strongly attract any steel or iron object held inside the frameWeak magnets will cause excessive rpm on No Load Current Draw, Electric Starter test