Royal Enfield CONSTELLATION 1958, Workshop Maintenance Manual

Page: 64 / 106

SECTION G1D
Lucas Rotating Magnet Magneto Model SR2
Used on 1956-59 Super Meter
1. General
The magneto rotor comprises a permanent
magnet fitted with two laminated pole shoes.
The stator consists of laminated pole pieces
bridged by a laminated coil core. The coil has
concentrically wound primary and secondary
windings.
The rotor is driven by the engine through an
automatic advance coupling and induces an
alternating magnetic field in the laminated iron
core of the coil. This field in turn induces
alternating voltages in the primary and
secondary windings of the coil. Magnetic flux
due to current flowing in the primary winding
tends to oppose any change in direction of the
magnetic field in the laminated iron core. In this
way, field reversals due to the rotating magnet
are delayed until the contact breaker opens. This
removes the restraining influence of the primary
winding and the consequent rapid reversal of the
magnetic flux linked with the coil causes a high
voltage to be induced in the secondary winding.
The body of the magneto is formed of a
single casting enclosed at the contact breaker
end by a moulded cover. The cover is designed
with the high tension cable outlets in a
downward direction, thus preventing the
retention
of moisture at the terminal
connections. The coil and capacitor are robustly
constructed and specially treated to withstand
very arduous conditions.
The automatic timing control is a
centrifugally operated mechanism enabling an
angular movement of the magneto rotor to occur
relative to the drive. The mechanism consists of
two members flexibly coupled by pivoted
spring-loaded governor weights and toggles. At
low engine speeds and during starting, the
weights are closed and a delayed spark is
produced. As the engine speed increases, the
governor weights swing out and advance the
rotor (and thus the cam and the spark) relative
to the drive.
2. Routine Maintenance
(a) Lubrication
TAKE GREAT CARE TO PREVENT
OIL OR GREASE GETTING ON OR NEAR
THE CONTACTS.
(i) After every 150 running hours (say 5,000
miles) remove the moulded cover and add a
FEW drops of thin machine oil to the visible
end of the contact breaker pivot post.
(ii) After 1,000 running hours (say 30,000
miles) remove the moulded cover and withdraw
the rotating electrode. Slacken the fixed-contact
plate securing screws and pivot the assembly to
the fullest extent of the adjusting slots. Slacken
the nut securing the end of the contact breaker
spring and lift off the moving-contact assembly.
Smear the pivot pin with a small quantity of
Mobilgrease No. 2 or its equivalent. Replace the
components in the reverse order of dismantling.
(iii) The magneto rotor is mounted on ball
bearings. These bearings are packed with high
melting point grease before leaving the factory
and require no attention for a considerable time.
About every two years, or when the engine is
undergoing a general overhaul; the magneto
should be dismantled by a Lucas Service Depot
or Agent and the bearings repacked with high
melting point GREASE
(b) Cleaning
(i) Occasionally remove the moulded cover
and wipe the inside of the cover with a soft dry
cloth.
Section G1d Page 1
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