9-S28
L4400 , WSM
ELECTRICAL SYSTEM
Commutator and Mica
1. Check the contact face of the commutator for wear, and grind the
commutator with emery paper if it is slightly worn.
2. Measure the commutator O.D. with an outside micrometer at
several points.
3. If the minimum O.D. is less than the allowable limit, replace the
armature.
4. If the difference of the O.D.’s exceeds the allowable limit, correct
the commutator on a lathe to the factory specification.
5. Measure the mica undercut.
6. If the undercut is less than the allowable limit, correct it with a saw
blade and chamfer the segment edges.
Brush Wear
1. If the contact face of the brush is dirty or dusty, clean it with emery
paper.
2. Measure the brush length (A) with vernier calipers.
3. If the length is less than the allowable limit, replace the yoke
assembly and brush holder.
W1143919
Commutator O.D.
Factory spec.
30.0 mm
1.181 in.
Allowable limit
29.0 mm
1.142 in.
Difference of O.D.'s
Factory spec.
Less than 0.02 mm
0.0008 in.
Allowable limit
0.05 mm
0.0020 in.
Mica undercut
Factory spec.
0.50 to 0.80 mm
0.0197 to 0.0315 in.
Allowable limit
0.20 mm
0.0079 in.
(1) Segment
(2) Undercut
(3) Mica
(a) Correct
(b) Incorrect
Brush length (A)
Factory spec.
15.0 mm
0.591 in.
Allowable limit
11.0 mm
0.433 in.
KiSC issued 07, 2007 A
Tractor Manuals Scotland - Please Do Not Copy
Tractor Manuals Scotland
