Royal Enfield SPRING FRAME O.H.V. 250cc CLIPPER 1954 Workshop Maintenance Manual page 39

ROYAL ENFIELD WORKSHOP MANUAL
This period of 100° embraces TWO peaks of
current from the rectifier, the SECOND of which
corresponds approximately with the firing point.
Without the battery there is, therefore, a danger
of a spark occurring at the first peak, i.e. about
60° too soon, which will, of course, cause
pre-ignition.
4. Warning Light
This, with a resistance in parallel, is placed in
series with the ignition coil and contact breaker.
It lights when the ignition is switched on and the
engine is stationary with contact points closed.
When running it glows very dimly since it passes
current momentarily every time the points close.
Failure of the bulb does not prevent the ignition
working since the resistance in parallel provides
an alternative path.
5. Timing
An automatic advance mechanism is provided
at the back of the contact breaker. This has a
range of approximately 12 1/2° on the half speed
shaft corresponding to 25° on the engine shaft.
The optimum ignition timing is 30° advance
so that in the fully retarded position the contact
points must open when the piston is 5° or about
1/64 in. before T.D.C.
To time the ignition proceed as follows :-
Switch off and check the maximum opening
of the points which must be .015-.018 in.
Unscrew and remove the centre screw
securing the contact breaker cam centre to the
shaft.
Loosen the centre from the shaft by screwing
a 5/16 in. B.S.F. bolt into the thread provided.
Loosen the two small screws which secure the
contact breaker base plate and set the plate
central in its slots. Tighten the screws.
Place the machine on the stand (packed if
necessary to lift the rear wheel clear of the
ground). Engage top gear and turn the engine by
rotating the back wheel until the piston is 1/64 in.
before the top of the compression stroke, as
measured by a rod or wire inserted through the
plug hole, both valves being closed.
Switch on the ignition and rotate the cam
centre in a clockwise direction (viewed from the
left side of the machine) until the warning lamp
lights up (or the ammeter indicates a discharge).
Continue rotating slowly until the lamp just goes
out (and the ammeter needle returns to zero)
indicating that the points have opened.
Give the cam centre a sharp tap endways to
secure it on the shaft and lock up tightly with the
centre screw.
Section G2c Page 4
Check timing by turning engine with back
wheel until warning light just goes out and see
that piston is 1/64 in. before the top of the
compression stroke.
If timing is slightly incorrect adjust by
loosening two screws which secure the contact
breaker base plate to its housing and turn the plate
clockwise to retard the timing, anti-clockwise to
advance it. The slots in the plate provide a range
of adjustment of approximately ± 6°.
6. Checking for Faults
If the ammeter does not show approximately
the rates of charge quoted in Subsection 2 (d) first
make sure that the ammeter itself is working
correctly. To do this switch on the lights which
should show about 5 amps. discharge for the
headlights and 1 amp. for the pilot lights, plus a
further 3-4 amps. if the engine has stopped with
the contact breaker closed, which should be
indicated by the warning light.
Assuming that the ammeter is reading
correctly, failure to charge may be due to a loose
connection or a "short" in the wiring system
which should be carefully examined. In particular
make sure that the connections between the stator
coils are not contacting either the inside of the
chaincase or cover or the pivot pin for the slipper
chain tensioner.
If no short or open circuit can be located test
the generator in the following way :-
(a) First disconnect leads from generator at the
plug and socket connections. Start the engine and
connect an A.C. voltmeter across the leads from
the generator. Reading when meter is connected
across yellow and brown, or green and brown,
should be 20 volts minimum at 3,000 r.p.m. and
up to 45 volts at top revs.
Resistance between yellow and brown should
be .65 ohms and between green and brown .35
ohms.
500 volts meger test to earth should be infinity
(minimum 1 meg ohm) test on any of these three
leads.
(b) Rectifier-if voltage reading from generator
is correct but similar readings are not obtained
between rectifier terminal 2 and earth when
switch is in positions (d), (e) or (f), substitute a
new rectifier. Do not loosen rectifier centre screw
as this will damage rectifier as will the drilling of
holes through the plates.
(c) Electrical circuit-check to diagram No.
2133. (Fig. 4).