SECTION C39
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AUTO ADVANCE UNIT
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The auto advance unit fitted behind the contact
breaker plate in the timing cover automatically and
progressively advances the ignition timing as the
engine speed increases, and returns it to the fully
retarded or static position when the engine stops.
To expose the mechanism, it is necessary to
remove the contact breaker plate complete, but
before doing so mark the exact position of the
plate so that when it is refitted the timing is not
disturbed.
Remove the contact breaker plate fixing screws
and take off the plate complete with the contact
sets. Ensure that the springs of the auto advance
unit are intact with the taper loops attached to
the pins. Check the automatic action by turning the
cam by hand to the fully advanced position in which
the bob weights will be fully extended. When the
cam is released, the springs should return the bob
weights to the static position. The longest weight
location pin must be in the radiused range slot
marked 12°.
Lubricate the mechanism sparingly. Do not over
lubricate as an excess of oil may reach the contact
breaker points. If the contact breaker plate has
been removed from its original position without
being marked, the ignition timing should be checked
and reset as in Section C38 when the plate has been
refitted.
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SECTION C40
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CONTACT BREAKER ASSEMBLY
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The Lucas contact breaker mounted in the timing
cover contains a separate contact set for each
cylinder (see Fig. C47). Each contact set has its
own mounting plate held to the circular base plate
by two screws (A), each mounting plate being
provided with a slot into which an eccentric headed
adjusting screw (B) is fitted. When the securing
screws are slackened, rotation of the eccentric
screw moves the mounting plate in relation to the
ignition cam. This permits a very accurate setting
of ignition timing for each cylinder.
Another eccentric headed screw (C) is located in a
slot in each fixed contact plate and provides
adjustment for the contact breaker points.
The baseplate is secured by two screws in elongated
holes. To advance the timing move the baseplate
clock-wise. To retard, move the baseplate
anti-clockwise.
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Adjusting Contact Breaker Points Gap
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Remove the spark plugs so that the engine can be
rotated easily by means of the kickstart pedal. An
examination of the cam will reveal a small mark
adjacent to the slot. This mark assists in
obtaining a uniform gap for each cylinder. Rotate
the engine until the nylon heel of the moving
contact registers with this mark and the points
will be in the fully open position. Using a 0.015
in. (0.38 mm) feeler gauge check the gap. If the
adjustment is correct, the gauge will be an easy
sliding fit. When adjustment is necessary, release
the fixed contact plate locking screw (D) (see Fig.
C47) rotate the eccentric screw (C) until the
correct gap is obtained. Retighten the locking
screw. Adjust the other contact set in a similar
manner.
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Maintenance of the Contact Breaker
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Every 5,000 miles (8,000 kilometres) the contact
breaker points should be examined to determine
their condition. Remove the nut securing the
contact breaker spring to the anchor post and lift
off the spring heel, together with the terminals,
insulating bush and the insulating washer. Remove
the fixed contact plate locking screw and take off
the fixed contact plate.
Points which are slightly burnt or pitted can be
smoothed with a fine carborundum stone and
afterwards cleaned with a brush moistened in petrol
or white spirit; if they are badly affected they
should be renewed.
Before reassembly, smear the contact breaker
pivot post and the cam very sparingly with Retinax
"A" grease and add three drops of engine oil to
each lubricating felt. When reassembling ensure
that the insulating washer, contact breaker spring,
terminal and insulating bush are fitted in the
order shown in Fig. C47 and that the terminal tags
are inside the curve of the spring. Finally retime
the ignition as described in Section C38.
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