ELECTRICAL EQUIPMENT—Q.8
To separate the armature shaft from the drive
end bracket, press the shaft out of the drive end
bracket bearing. When fitting the new armature,
support the inner journal of the ball bearing,
using a mild steel tube of suitable diameter,
whilst pressing the armature shaft firmly home.
See also Para 4 (h)1.
(f)
Field Coils
Measure the resistance of the field coils, without
removing them from the dynamo yoke, by
means of an ohm meter connected between the
field terminal and the yoke. The resistance is
6.0 ohms for the model C40A.
If an ohm meter is not available, connect a 12
volt d.c. supply between the field terminal and
dynamo yoke with an ammeter in series. The
ammeter reading should be approximately 2
amperes. Zero reading on the ammeter or an
"Infinity" ohm meter reading indicates an open
circuit in the field winding.
If the current reading is much more than 2
amperes, or the ohm meter reading much below
6 ohms, it is an indication that the insulation of
one of the field coils has broken down.
In either event, unless a substitute dynamo is
available, the field coils must be replaced. To
do this, carry out the procedure out-
Fig. Q.5.
Tightening Pole Shoe Retaining Screws.
lined below, first noting to which end of the coil
the field terminal is soldered.
1.
Drill out the rivet securing the field coil terminal
assembly to the yoke and unsolder the field coil
connections.
2.
Remove the insulation piece which is provided
to prevent the junction of the field coils from
contacting with the yoke.
3.
Mark the yoke and pole shoes so that the latter
can be refitted in their original positions.
4.
Unscrew the two pole shoe retaining screws by
means of a wheel operated screw driver.
5.
Draw the pole shoes and field coils out of the
yoke and lift off the coils.
6.
Fit the new field coils over the pole shoes and
place them in position inside the yoke. Take
care to ensure that the taping of the field coils is
not trapped between the pole shoes and the
yoke.
7.
Locate the pole shoes and field coils by lightly
tightening the fixing screws.
8.
Fully tighten the screws by means of a wheel
operated screwdriver.
9.
Solder the original terminal and earthing eyelet
to the appropriate coil ends.
10.
Refit the insulating sleeve and re-rivet the
terminal assembly to the yoke.
11.
Refit the insulation piece behind the junction of
the two coils.
(g)
Bearings
Bearings which are worn to such an extent that
they will allow side movement of the armature
shaft must be replaced. To replace the bearing
bush in a commutator end bracket proceed as
follows:—
