Check the mica depth (A). If the mica is too high (B), undercut the mica with a hacksaw blade to the proper depth. Cut away all the mica (C) between the commutator segments. The undercut should not be too shallow, too narrow, or V-shaped (D).

Commutator Mica Depth
Standard (New):	0.40−0.50 mm (0.016−0.020 in.)
Service Limit:	0.15 mm (0.006 in.)