2006 Johnson SD 30 HP 4 Stroke Outboards Service Manual, PN 5006592, Page 235Get this manual
POWER TRIM AND TILT PTT MOTOR Inspect the surface of the commutatorIf the surface is gummy or dirty, clean the surface with 400 grit emery paperUse vernier calipers to measure the outside diameter of the commutatorCommutator Outside Diameter Standard 0.77 in(19.5 mm) Service limit 0.73 in(18.5 mm) If the measurement exceeds the service limit, replace the armatureIf the undercut is less than the service limit, cut the mica to the specified depthUse compressed air to remove all particles of mica and metal
Brushes
Use vernier calipers to check the length of each brushBrush Length Standard 0.39 in(9.8 mm) Service limit 0.19 in(4.8 mm) If the brushes are worn down to the service limit, replace the brushes