What is the minimum commutator diameter for the starter armature?

31 mm (1.22 in). If the commutator measures less than this specified value, replace it.

What should I do if the commutator surface is rough?

Sand it lightly with No. 500 - 600 sandpaper.

What is the specified insulating mica undercut depth?

If the mica depth from the commutator surface is less than 0.2 mm (0.008 in), undercut it to 0.5 - 0.8 mm (0.020 - 0.031 in).

How do I test the armature for continuity and insulation?

Perform a continuity test between two segments side by side with an ohmmeter — no continuity means replace. Then perform an insulation test between each commutator bar and the shaft — if continuity exists, replace.

What does a correct mica undercut look like?

The undercut should be squared (cut with a file) to 0.5 - 0.8 mm depth; a rounded undercut between segments is shown as incorrect.

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Nissan Micra Starter Armature Check - Commutator & Mica Specs (EL-20)

Service manual page: starter armature continuity, commutator, and mica checks

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Service manual page covering starter armature continuity, commutator diameter, and undercut mica inspection.

AI caption February 2006 · Photo 366 of 412

This is page EL-20 from a Nissan service manual covering the Starting System (Starter), specifically the Armature Check procedure. It describes five inspection steps for a starter motor armature: (1) a continuity test between two adjacent commutator segments using an ohmmeter — replace the armature if there is no continuity; (2) an insulation test between each commutator bar and the shaft — replace if continuity exists; (3) inspection of the commutator surface — if rough, sand lightly with No. 500-600 sandpaper; (4) measurement of the commutator diameter with a vernier caliper, with a minimum diameter specification of 31 mm (1.22 in) — replace if below spec; and (5) checking the depth of the insulating mica below the commutator surface — if less than 0.2 mm (0.008 in), undercut the mica to 0.5-0.8 mm (0.020-0.031 in). Illustrations show the ohmmeter/multimeter test setups, sanding procedure, caliper measurement, and correct vs. incorrect mica undercut profiles (a file is used, with the correct undercut squared and the incorrect one rounded). Figure reference codes SEL625B, EE022, SEL624B, SEL418A, and EE021 appear with the illustrations.

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Frequently asked questions

What is the minimum commutator diameter for the starter armature?: 31 mm (1.22 in). If the commutator measures less than this specified value, replace it.
What should I do if the commutator surface is rough?: Sand it lightly with No. 500 - 600 sandpaper.
What is the specified insulating mica undercut depth?: If the mica depth from the commutator surface is less than 0.2 mm (0.008 in), undercut it to 0.5 - 0.8 mm (0.020 - 0.031 in).
How do I test the armature for continuity and insulation?: Perform a continuity test between two segments side by side with an ohmmeter — no continuity means replace. Then perform an insulation test between each commutator bar and the shaft — if continuity exists, replace.
What does a correct mica undercut look like?: The undercut should be squared (cut with a file) to 0.5 - 0.8 mm depth; a rounded undercut between segments is shown as incorrect.