The Control Box - MG MGA Twin Cam Workshop Manual

retaining ring " L."
Note-Should either the control nut or screwed sleeve be damaged, a replacement assembly,
consisting of a screwed sleeve and control nut, must be fitted. These components must not be fitted
individually.
Commutator
A commutator in good condition will be smooth and free from pits and burned spots. Clean the
commutator with a cloth moistened with petrol. If this is ineffective, carefully polish with a strip of fine
glass-paper, while rotating the armature. To remedy a badly worn commutator, dismantle the starter
drive as described above and remove the armature from the end bracket. Now mount the armature in
a lathe, rotate it at a high speed and take a light cut with a very sharp tool. Do not remove any more
metal than is absolutely necessary, and finally polish with very fine glass-paper.
The mica on the starter commutator must not be undercut,
Field coils
The field coils can be tested for an open circuit by connecting a 12-volt battery, having a 12-volt bulb in
one of the leads, to the tapping point of the field coils to which the brushes are connected, and the
field terminal post. If the lamp does not light, there is an open circuit in the wiring of the field coils.
Lighting of the lamp does not necessarily mean that the field coils are in order, as it is possible that
one of them may be earthed to a pole shoe or to the yoke. This may be checked by removing the lead
from the brush connector and holding it on a clean part of the starter yoke. Should the bulb now light it
indicates that the field coils are earthed.
Should the above tests indicate that the fault lies in the field coils, they must be renewed. When
renewing field coils carry out the procedure detailed in the Dynamo Section N.5.
Armature
Examination of the armature will in many cases reveal the cause of failure, e.g. conductors lifted from
the commutator due to the starter being engaged while the engine is running and causing the
armature to be rotated at an excessive speed. A damaged armature must in all cases be renewed-no
attempt should be made to machine the armature core or to true a distorted armature shaft.
Bearings (commutator end)
Bearings which are worn to such an extent that they will allow excessive side play of the armature
shaft must be renewed. To renew the bearing bush, proceed as follows: -
Press the new bearing bush into the end bracket, using a shouldered mandrel of the same diameter
as the shaft which is to fit in the bearing.
The bearing bush is of the porous phosphor bronze type, and before fitting, new bushes should be
allowed to stand completely immersed for twenty-four hours in thin engine oil in order to fill the pores
of the bush with lubricant.
Reassembly
The reassembly of the starter is a reversal of the operations described in this section.
N.9 THE CONTROL BOX
Regulator adjustment
The regulator is carefully set before leaving the Works to suit the normal requirements of the standard
equipment, and in general it should not be necessary to alter it. If, however, the battery does not keep
in a charged condition, or if the dynamo output does not fall when the battery is fully charged, it may
be advisable to check the setting and, if necessary, to readjust it.
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