Norton Commando Workshop Manual

## Electrical

# J

### IGNITION COILS LUCAS TYPE 17M6 (6 Volt)

1971 and later Models
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.

### IGNITION COILS LUCAS TYPE 17M12

(12 Volt) - Certain 1972 Models
Twelve volt ignition coils, again of the oil filled, sealed type, are used on some models and require no ballast resistor.

### TESTING AN IGNITION COIL

(17M6 and 17M12 Types)
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.
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.

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.

### BALLAST RESISTOR

(With 6 volt coils, 1971 and later Models)
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.

### CONTACT BREAKER ASSEMBLY - LUCAS TYPE 6CA

The contact breaker and auto advance mechanism are covered fully in Section C39 & C40 adjacent to engine ignition timing details.

### SECTION J13

### CAPACITOR PACK TESTING

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.

### CHANGING A CAPACITOR

(1971 and later Models)
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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