Royal Enfield SPRING FRAME O.H.V. 250cc CLIPPER 1954 Workshop Maintenance Manual page 38

ROYAL ENFIELD WORKSHOP MANUAL
rotor is therefore keyed on the shaft with its pole
pieces in such a position that the "inner" ends of
the coils are positive and current is flowing as
described through circuit (ii), immediately
before the contact points open with the
automatic advance fully retarded. When the
engine has started, the automatic advance
mechanism comes into operation so that the
contact points open before the rotor has reached
its optimum position. This weakens the spark
and produces misfiring which prevents the
engine running at high speeds unless the switch
is moved to the "IG and CH" position. At higher
speeds further advance brings the previous pole
of the rotor into operation and a good spark is
again obtained with the current at the point of
opening of the points flowing through circuit (i)
(see above).
Note. The position of the keyway in the rotor
depends on the method of mounting the stator
(see Subsection 1). Some rotors have two
keyways in them, in this case note which was in
use and replace the same way. Some early rotors
had the keyway not in the centre of a pole piece,
in this case the rotor must be replaced the same
way round. Incorrect positioning of the rotor
can affect only the emergency start, it can have
no effect on the charge rates.
Ignition and Charge. The current is taken
from two of the generator coils on either of the
two following circuits, depending on the
instantaneous direction of the A.C. voltage. If
the inner ends of the generator coils are positive,
current flows from them to terminal 1 of the
rectifier, through the rectifier plate to the
positive terminal (or centre screw) which is
earthed and thence through the battery from
positive to negative, thus charging the battery.
The return circuit is through the ammeter to
terminal 6 of the switch and thence to terminal 2
of the rectifier through the rectifier plate to
terminal 3, then to terminals 3 and 4 of the
switch and so back to the outer ends of the
generator coils.
If the outer ends of the generator coils are
positive current flows from them to terminals 3
and 4 of the switch, then to terminal 3 of the
rectifier, through the rectifier plate to the
positive rectifier terminal (or centre screw)
which is earthed, and thence through the battery
from positive to negative thus charging the
battery. The return circuit is through the
ammeter to terminal 6 of the switch and thence
to terminal 2 of the rectifier, through the rectifier
plate to terminal 1 and so back to the inner ends
of the coils. Switch terminal 6, being connected
through the ammeter to the battery negative
terminal, is always at negative voltage relative to
earth or the frame of the machine. When the
engine is running at a moderate or high speed
the negative voltage is increased on account of
the connection to the negative (No. 2) terminal
of the rectifier. When the contact breaker points
are closed, therefore, current flows from earth
through them and the primary winding of the
ignition coil to terminal 1 of the switch, thence
through the warning light (and its resistance in
parallel) to terminal 9 of the switch and so to
terminal 6. The return circuit if the engine is not
running is through the ammeter to the battery
negative terminal. When the engine is running
the current will return to earth through the four
plates of the rectifier.
Headlight. With the switch in the "H"
position the charging circuit is the same as
described above, with the exception that the
remaining four coils of the generator are brought
into operation owing to the fact that the switch
then makes contact between the terminals 2 and
3 as well as 3 and 4. Current from earth flows
through one of the headlamp filaments to the
dip-switch and then to terminal 8 of the battery,
also through the tail and speedometer lights to
terminal 7. Both terminals 8 and 7 are connected
to 6 and the return circuit is either through the
ammeter to the battery negative terminal or
through the rectifier, depending on whether or
not the engine is running. Since the output from
the rectifier is limited by the capacity of the
generator the current taken by the lamps
naturally reduces the rate of charge through the
battery, which would otherwise be excessive
with six generator coils in use.
Pilot Light. With the switch in the pilot light
position the contact between terminals 4 and 3
of the switch is broken so that only four of the
generator coils remain in use. Terminal 6 of the
switch is connected to 5, 7 and 9 but not to 8 so
that current flows through the pilot bulb but not
through the main headlamp bulb.
It will be noted from the above that the
battery (even if completely discharged) should
be included in the circuit if the "emergency
start" position of the switch is to operate
satisfactorily. (Alternatively the lead normally
connected to the battery negative terminal can
be earthed.) The battery is also necessary in
switch positions (d), (e) and (f) in order to
prevent excessive voltage rise which might burn
out the lamp bulbs and/or ignition coil. The
battery also smoothes out the "peaks" of the
uni-directional current from the rectifier and
thus prevents the possibility of a spark occurring
at the crest of the first "peak" after the contact
points are closed. The points must be closed for
about 100° in order to ensure a good spark at
high speeds when running on the smooth current
obtained when the battery is in the circuit.
Section G2c Page 3