Mechanical contact breaker - points servicing

Ignition system / Mechanical contact breaker - points servicing

1 At the intervals specified in “Routine Maintenance”, prise down the clips on the distributor cap and place the cap with high tension leads to one side.

2 Pull off the rotor.

3 Remove the spark shield. Mechanical wear of the contact breaker reduces the gap.

Electrical wear builds up a “pip” of burned metal on one of the contacts. This |prevents the gap being measured for re-adjustment, and also spoils the electric circuit.

Ducellier type distributor 4 To remove the contact breaker movable arm, extract the clip and take off the washer from the top of the pivot post.

5 Extract the screw and remove the fixed contact arm.

6 Clean the points by rubbing the surfaces on a fine abrasive such as an oil stone. The point surface should be shaped to a gentle convex curve. All the “pip” burned onto one contact must be removed. It is not necessary to go on until all traces of the crater have been removed from the other. There is enough metal on the contacts to allow this to be done once. At alternate services, fit new points.

Wash debris off cleaned points and preservatives off new ones.

7 Now the distributor should be lubricated.

This lubrication is important for the correct mechanical function of the distributor, but excess lubrication will ruin the electrical circuits, and give difficult starting.

8 Whilst the contact breaker is off, squirt some engine oil into the bottom part of the distributor, onto the centrifugal advance mechanism below the plate.

9 Wet with oil the felt pad on the top of the distributor spindle, normally covered by the rotor arm.

10 Put just a drip of oil on the pivot for the moving contact.

11 Smear a little general purpose grease onto the cam, and the heel of the moving contact breaker.

12 Refit the contact points and then set the gap in the following way.

13 Turn the crankshaft by applying a spanner to the pulley nut or by jacking up a front wheel, engaging top gear and turning the roadwheel in the forward direction of travel. Keep turning until the plastic heel of the movable contact arm is on the high point of a cam lobe on the distributor shaft.

14 Set the points gap by moving the fixed contact arm until the specified feeler blades are a sliding fit. Tighten the fixed contact arm screw.

15 Check the contact end of the rotor arm.

Remove any slightly burnt deposits using fine abrasive paper. Severe erosion will necessitate renewal of the rotor.

16 Wipe out the distributor cap and check for cracks or eroded contacts (photo). Renew if evident or if the carbon brush is worn.

2.16 Interior of distributor cap showing carbon brush

17 Refit the spark shield, rotor and distributor cap.

18 Setting the contact breaker gap with a feeler blade must be regarded as a means of ensuring that the engine will start. For optimum engine performance, the dwell angle must be checked and adjusted as described in Section 3.

Marelli type distributor 19 Open the points with a finger nail and inspect their condition. If they are badly eroded or burned, then they must be renewed. The contact points can only be renewed complete with carrier plate as an assembly.

20 Release the low tension leads from the terminals on the distributor body (photo).

2.20 Marelli distributor

21 Extract the screws which hold the vacuum advance capsule to the distributor body. Tilt the capsule and release its link rod from the contact breaker carrier plate (photo).

2.21 Extracting vacuum diaphragm unit screw

22 Prise out the E-clip from the breaker carrier and then withdraw the contact assembly from the top of the distributor shaft.

Note the washers above and below the contact assembly (photos).

2.22A Marelli contact breaker E-clip

2.22B Washers above contact breaker

23 Fit the new contact assembly by reversing the removal operations.

24 Although the points gap is normally set in production, check it using feeler blades when the plastic heel of the movable arm is on a high point of the shaft cam. Adjust if necessary by inserting an Allen key (3.0 mm) into the socket-headed adjuster screw.

25 Carry out the operations described in paragraphs 14 to 17 in this Section.

Fig. 4.3 Marelli contact breaker (Sec 2)

Fig. 4.4 Adjusting Marelli type contact breaker points gap (Sec 2)