BSA D14/4 BANTAM SUPREME D14/4 BANTAM SPORTS, Workshop Manual

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D14/4 ELECTRICAL SYSTEM G8
Ignition Coil
Firstly, completely disconnect the ignition coil from
the motor-cycle circuit, and connect the D.C.
voltmeter across the six-volt battery to produce a
continuity check. The meter should register the battery
voltage. Now break this circuit at any point and across
this break connect the two small screw terminals of the
ignition coil. This test will indicate continuity to prove
that the primary winding is intact. Likewise, one lead
of the test circuit connected to either one of the
primary terminals and the other to the high-tension
pick-up will again show continuity. A lower reading
can be expected due to the higher resistance of the
secondary windings.
The third and last check is to ensure that the coil is
not earthing out. Leave one lead attached to one of the
primary terminals and connect the other to the coil
case, when no reading should show. Similar results
should be noted at the high-tension pick-up point.
Where an ohm meter is available, check the
resistance as below:—
Primary resistance
Secondary resistance 1·3 ohms
4,500 ohms
A defective primary winding may continue to
produce a weak spark whereas intermittent
performances will invariably be caused by a faulty
secondary. Should there be any possible doubt about
the ignition coil, however, a final check can be made
by substitution.
Constructing a 1 ohm Load Resistor
The resistor used in the above tests must be accurate
and constructed so that it will not over-heat otherwise
the correct values of current or voltage will not be
obtained.
A suitable resistor can be made from 4 yards (3¾
metres) of 18 s.w.g. (·048",
i.e., 1·2 mm. diameter)
Nichrome wire by bending it into two equal parts and
calibrating it as follows.
(1) Fix a heavy gauge flexible lead to the folded end
of the wire and connect this lead to the positive
terminal of a six-volt battery.
(2) Connect a D.C. voltmeter (0-10 volts) across the
battery terminals and an ammeter (0-10 amp.)
between the battery negative terminal and the
free ends of the wire resistance, using a crocodile
clip to make the connection.
(3) Move the clip along the wires, making contact
with both wires until the ammeter reading is
numerically equal to the number of volts shown
in the voltmeter. The resistance is then 1 ohm.
Cut the wire at this point, twist the two ends
together and wind the wire on an asbestos former
approximately 2" (5 cm.) diameter so that each
turn does not contact the one next to it.
BUSHMAN PASTORAL MODELS
The Pastoral models are not fitted with a battery and
the electrical equipment will only function when the
engine is running.
The electrical system is fed by a Wipac series 114
six-pole alternator comprising a six-pole magnetic
rotor and a laminated stator plate fitted with six feed
coils. Issuing from the alternator is a group of five
wires, translucent, brown/black, maroon, brown and
dark red. The translucent lead is common to all coils.
A schematic diagram of the alternator is shown in
Fig. G5.
(1) The headlight, tail light and speedometer light
take their supply between the translucent and
dark red leads utilising two of the six alternator
coils.
(2) The stop light is fed between the brown and
translucent lead utilising one alternator coil.
(3) The ignition system which operates on an energy
transfer basis is fed between the maroon and
translucent leads and uses one alternator coil.
(4) Provision is made for the operation of an A.C.
horn which is operated by two alternator coils
between the brown/black and translucent leads.
No provision is made for parking lights.