Norton Commando Workshop Manual

## Engine/Primary Transmission

# C

### SECTION C39

### AUTO ADVANCE UNIT

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.

### SECTION C40

### CONTACT BREAKER ASSEMBLY

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.

Adjusting Contact Breaker Points Gap
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.
Maintenance of the Contact Breaker

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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