Commutator End Bracket; Drive Clutch - MG MGB Workshop Manual

THE ELECTRICAL
SYSTEM
N
19.
Check the brush spring pressure. Each spring should
exert a minimum
of 36 02. (1.02 kg.) with a new
(full-length) brush in position.
COMMUTATOR
20.
21.
The commutator
should be burnished,
free of pits or
burned
spots,
and
can
be cleaned
with
a
petrol-moistened
cloth.
If this cleaning is ineffective,
spin the armature
and polish the commutator with
■ne glass-paper, removing all abrasive dust with a dry
air blast.
In the case of a badly worn commutator,
mount the
armature
between centres in a lathe and rotate it at
high speed. Take a light cut with a very sharp tool and
do not remove more metal than is necessary to clean
the
commutator.
Finally,
polish with
very
fine
glass-paper. The insulators between the commutator
segments must not be undercut.
ARMATURE
22.
23.
24.
Examine
the armature for conductors which have
lifted from the commutator risers. This would indicate
overspeeding and the drive clutch should be checked
(see 28).
Check for signs of the armature fouling the pole shoes
indicating a distorted armature shaft or worn bearings
(see 29 and 30). Do not attempt to machine the
armature core or to true a distorted shaft; a damaged
armature must be renewed.
To make a thorough
check on the condition of the
armature
it
should be tested on a 'growler'. The
armature
insulation
can be checked by means of a
110-volt A.C.
test lamp connected between each
commutator
segment in turn and the armature shaft.
The test lamp should not light.
FIELD COILS
25.
MGB.
Test the ■eld coils for continuity. Ensure that both
brushes and their ■exible connectors are clear of the
yoke and connect a 12-volt test lamp and battery
between the cable connection to 'STA' and each of
the ■eld coil brushes in turn. If the lamp does not
light, an open circuit in the ■eld coil is indicated and
they should be renewed as follows:
a.
Using a wheel-operated screwdriver, unscrew the
four pole-shoe retaining screws.
b. Withdraw the inter-coil
connector
insulating
piece and remove the pole shoes and coils from
the yoke.
0.
Fit new coils to the pole shoes and position them
inside the yoke. Make sure that the coil taping is
not
trapped between the pole shoes and the
yoke, then lightly tighten the pole-shoe retaining
screws.
d. Fit the insulator to the ■eld coil terminal
and
position the inter-coil connection insulator inside
the yoke. Hold the pole shoes in position with a
pole-shoe
expander and tighten
the retaining
screws with a wheel-operated
screwdriver.
Issue 8. 82448
26. Test the ■eld coils for insulation from the yoke.
Ensure that both brushes and their ■exible connectors
are clear of the yoke and connect
a 110-volt A C.
test-lamp between the terminal
post and the yoke. If
the lamp lights, earthing of the ■eld coils is indicated
and they should be renewed as described in 25 a to d.
COMMUTATOR END BRACKET
27.
Clean all traces of brush deposit from the commutator
end bracket and connect
a 110-volt A.C. test lamp
between the end bracket and each insulated brush box
in
turn.
If the lamp lights, faulty
insulation
is
indicated and the commutator
end bracket should be
renewed.
DRIVE CLUTCH
28.
Check the operation
of the drive clutch. It should
provide
instantaneous
take-up
of the drive in one
direction,
yet rotate
easily and smoothly
in
the
opposite direction. It should also move freely on the
armature
shaft
splines without
any
roughness
or
tendency to bind.
BEARINGS
29.
30.
Renew the bearings which are worn to such an extent
that they allow excessive side-play of the armature
shaft. Remove the bearing from the commutator
end
bracket by screwing a tap squarely into the bearing and
withdrawing the bearing with the tap. The drive end
bracket bearing can be pressed out.
Press
the
new
bearings into position using
a
shouldered highly
polished mandrel
.0005 in. (0.13
mm.) larger in diameter than the shaft which will run
in the bearing.
NOTE.— The
commutator
and drive end bracket
bearings are porous bronze and should be immersed in
clean engine oil for 24 hours before
■tting.
In an
emergency this period may be reduced by maintaining
the oil at a temperature
of 100°C. (212°F.) for two
hours and allowing the oil to cool before removing the
bearing. Porous bronze bushes should not be reamed,
as the porosity of the bush would be impaired.
Reassembling
31.
During reassembly lubricate
all moving
parts with
Shell Retinax A grease, or an equivalent.
32. Reassemble the
starter motor
by
reversing the
procedure in 6 to 16.
33.
Set the pinion travel as follows:
a.
Connect a 6-volt supply, with a switch in circuit,
between the small unmarked solenoid terminal
and earth. The period of energization
should be
kept as brief as possible to avoid overheating the
series winding.
N35