Removing & replacing contact points

Part 1. Preparation and safety

Objective

• Remove and replace a vehicle’s contact points.

Personal safety

Whenever you perform a task in the workshop you must use personal protective clothing and equipment that is appropriate for the task and which conforms to your local safety regulations and policies. Among other items, this may include:

• Work clothing - such as coveralls and steel-capped footwear
• Eye protection - such as safety glasses and face masks
• Ear protection - such as earmuffs and earplugs
• Hand protection - such as rubber gloves and barrier cream
• Respiratory equipment - such as face masks and valved respirators

If you are not certain what is appropriate or required, ask your supervisor.

Safety check

• When disconnecting a battery always disconnect the negative terminal first.
• When reattaching a battery always attach the negative terminal last.
• Do not wear jewelry that may cause a short circuit with an electrical connection.
• Distributors can get quite hot in operation. Make sure you test the temperature of the distributor before you handle it.
• Always wear protective clothing and the appropriate safety equipment.
• Make sure that you understand and observe all legislative and personal safety procedures when carrying out the following tasks. If you are unsure of what these are, ask your supervisor.

Points to note

• Even though most vehicle electrical systems are described as being 12 volt, they operate at between 13.8 to 14.2 volts. The voltage handled by an ignition system that uses contact breaker points carries between 12,000 - 25,000 volts in the secondary circuit of the system. Therefore care must be taken when the ignition system is activated.
• The contact breaker points are normally found in the base of the distributor below the distributor cap and the rotor.

• Contact breaker points need to be changed at regular service intervals according to the manufacturer's instructions.
• During operation the point contacts transfer material from one surface to another. If this results in a build up greater than 1 mm the Capacitor, or Condenser as it is more commonly known, should be replaced.
• The distributor cap is made of a hard plastic-like material that can easily break and shatter. Be careful when handling it.
• The distributor also contains two types of ignition advance and retard units: a mechanical or "Load Sensitive" unit and a vacuum or "Speed Sensitive " unit. These units should also be checked periodically.

• A Dwell meter can be used to diagnose faults in the distributor. Dwell is the amount of time that the points remain closed from one part of the rotation of the distributor shaft to the next. The correct dwell angle is very important. A variation in the reading outside of the manufacturer's specifications indicates wear in the distributor itself. In some cases the dwell can be brought back to within acceptable limits by adjusting the points irrespective of the desired points gap.

Part 2: Step-by-step instruction

1. Locate the distributor and remove the cap
   The contact breaker points are found in the base of the distributor below the distributor cap and the rotor. Remove the cap by unclipping the fasteners and carefully locate the cap in a position adjacent to the distributor. Now remove the rotor making note of its position and locating method.
2. Rotate the engine
   Make sure the vehicle is in neutral. Carefully rotate the engine by hand using an appropriate tool on the engine pulley until the points are at their widest opening. This is where the heel of the rubbing block of the contact breaker points rides on the cams of the distributor shaft and opens the points as it rotates.
3. Remove the contact breaker points
   Unclip the small electrical leads from the ignition coil and capacitor at the back of the points. There are various methods of fixing these so be sure to follow the instructions in the service manual. Remove the locating screw from the contact breaker point base plate. Then remove the points from the base of the distributor.
4. Inspect the points
   Inspect the contact breaker points for their condition. Small indications of pitting are quite normal, however a transfer of more than 1 mm of tungsten material from one side of the points to the other, indicates that the capacitor may also need changing.
5. Check mechanical advance and retard weights
   At longer servicing intervals it is good practice to inspect the condition of the mechanical advance and retard units balance weights. Remove the distributor base plate, and check to see that the weights can be moved on their locating points freely, and that the restraining springs are in place and in good order. If necessary, apply a small amount of the manufacturer’s specified lubricant, to ensure that the weights remain serviceable until the next inspection. Seized weights can severely affect the vehicles performance and economy. Refit the distributor base plate in its correct location and ensure that the capacitor if located on the base plate is secure.
6. Check the vacuum advance unit
   Vacuum load sensitive advance and retard units can be checked by attaching a vacuum source to the end of the unit and watching to see if the base plate moves in relation to its reference points. When the vacuum source is removed the base plate should move back to its static position.
7. Fit the contact breaker points
   After cleaning the new points to remove all signs of protective coating, locate the new contact breaker points on the base plate and replace the locating screw, leaving it loose enough to allow the points to be moved in relation to the base plate. Refit the electrical connections from the ignition coil and the capacitor.
8. Adjust the contact breaker points
   Adjust the points by locating the heel of the rubbing block of the contact breaker points so it rides on the cam of the distributor shaft. Using a feeler gauge of the correct manufacturers specifications, gently adjust the points with a screwdriver until the points gap is in accordance with specifications. Then tighten the locating screw and recheck the gap setting.
9. Check the dwell
   Replace the rotor and the distributor cap and start the vehicle. Once the components have been reassembled a dwell meter can be used to check the overall condition of the distributor. With the engine running and the dwell meter connected rev the engine and hold the engine speed at approximately 2500 - 3000 RPM. If the dwell meter shows a variation in the reading outside of the manufacturers specifications, there are signs of wear in the distributor itself. In some cases the dwell can be brought back to within acceptable limits by adjusting the points irrespective of the desired points gap.
10. Clean up
    Remove the fender covers and return any tools used to their correct place.