IGNITION COILS LUCAS TYPE 17M6 (6 Volt)
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1971 and later Models
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Six volt ignition coils are usad in conjunction
with a ballast resistor to allow their use in an
otherwise 12 volt electrical system. This system
has been adopted since an adequate spark is
available with the battery in a heavily discharged
state. The ignition coils are sealed units,
requiring only a periodic check on connections.
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IGNITION COILS LUCAS TYPE 17M12
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(12 Volt) - Certain 1972 Models
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Twelve volt ignition coils, again of the oil
filled, sealed type, are used on some models and
require no ballast resistor.
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TESTING AN IGNITION COIL
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(17M6 and 17M12 Types)
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An electrical test set is necessary for full
testing of the ignition coil and though a similar
set-up can be produced as shown in Fig. J5
provision will have to be made for a contact
breaker which can be motored at 100 r.p.m. Use a 6
volt battery for this test.
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Before commencing the main test, check the
condition of the primary windings. This is done by
connecting an ohmeter across the low tension
terminals. At 20°C the minimum resistance
should be 1.7 ohms and maximum resistance, 1.9 ohms
for 17M6 (6 volt) coils and 3.3 ohms minimum and
3.8 ohms maximum resistance for 17M12 (12 volt)
coils.
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Set the adjustable gap to 8 mm for the 6 volt
coil or 9 mm for the 12 volt coil and connect up as
in Fig. J5. If the coil is in good condition,
sparking should occur regularly with no more than
5% missing per 15 seconds.
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BALLAST RESISTOR
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(With 6 volt coils, 1971 and later
Models)
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This permits the use of 6 volt coils in an
otherwise 12 volt system. The two coils are wired
in parallel with the resistor in series. When the
battery voltage has dropped due to the heavy
current taken such as by the use of an electric
starter, the ignition coils are fed direct,
bypassing the resistor and thus enabling the coils
to work at their approximate potential. The ballast
resistor can only be tested against its resistance
value of 1.8-2 ohms.
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CONTACT BREAKER ASSEMBLY - LUCAS TYPE 6CA
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The contact breaker and auto advance mechanism
are covered fully in Section C39 & C40 adjacent
to engine ignition timing details.
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SECTION J13
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CAPACITOR PACK TESTING
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The capacitors can be tested in situ. To test,
turn on the ignition and take voltage readings
across each set of contacts when opeh. If no
reading is gained, the capacitor is unserviceable
due to a breakdown of the internal insulation. If a
reading is gained but the capacitor has reduced
capacity, evidenced by excessive arcing and severe
burning of the contact points, a new capacitor
should be substituted on the affected cylinder.
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CHANGING A CAPACITOR
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(1971 and later Models)
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Remove the complete coil cluster (see Section
C1). Release the capacitor pack (2 screws and
nuts). Remove the rubber cover: the individual
capacitors are retained to the base plate by single
nuts.
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