Royal Enfield SPRING FRAME O.H.V. 250cc CLIPPER 1954 Workshop Maintenance Manual page 43

ROYAL ENFIELD WORKSHOP MANUAL
Connections to the remaining coils vary
according to the position of the lighting and
ignition switch controls, as shown schematically
in Fig. 3.
In the " OFF " and " PILOT " positions two
pairs of coils are disconnected and only the third
pair is in use. Current flows from these through
the rectifier and battery, taking one of two
alternative paths (indicated by the arrows on the
rectifier diagram) according to the instantaneous
polarity at the alternator coils. Thus the rectifier
acts as an electrical non-return valve converting
the A.C. current from the alternator into
unidirectional current, which trickle charges the
battery as well as energising the ignition coil. In
the " HEAD " position the alternator output is
increased by connecting all three pairs of coils in
parallel, thus providing current for the headlight,
tail and speedometer lights in addition to the
ignition and a trickle charge to the battery.
1 (c). Emergency Starting
An emergency starting position is provided on
the ignition switch. This switch is for use if the
battery has become discharged and a normal start
cannot be made. In the switch position "EMG"
the alternator is connected directly to the ignition
coil and this allows the engine to be started
independently of the battery (see Fig. 4). During
the closed period of the contact points, pulses of
unidirectional current pass from the upper end of
the two left alternator coils (Fig. 4) through the
top right hand plate of the rectifier and the
contact points back into the left hand alternator
coils.
Section G2d Page 2
If the opening of the contact points is timed to
coincide with one of these pulses there will be
sufficient energy present in the system to
overcome the impedance of the primary winding
of the ignition coil and the voltage of the battery,
thus causing a pulse of current to pass through
the primary of the ignition coil and so create
sufficient voltage in the secondary winding to
provide a good spark at the plug. The advantage
of this system is that the primary of the ignition
coil is short circuited during the closed period of
the contact breaker so that no unwanted sparks
can occur on the compression stroke of the
engine. Note that, if the battery is removed, the
emergency start will not function unless the lead
normally connected to the battery negative
terminal is earthed. The emergency start system
functions better with a discharged battery than
with a fully charged one.
Proper functioning of the emergency starting
feature is dependent on accurate ignition timing
being observed and correct contact breaker gap
being maintained. After starting has been
effected the ignition switch should be turned to
the normal running " IGN "position.
1 (d). Direct Operation
Short journeys without the battery can be
made with the switch in the " EMG "position. To
do this, the cable normally connected to the
battery negative terminal must be connected to
an earthed point on the machine. If lights are
required when the battery is disconnected, use
only the headlights and keep the engine speed
low to prevent excessive voltage rise.
2. Routine Maintenance
The alternator and rectifier require no
maintenance apart from ensuring that all
connections are clean and tight.
If the rotor, stator, engine crankshaft or rear
half of the chaincase have been disturbed, the air
gap between the rotor and stator should be
checked.