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Ignition – Condensers, Contact Sets, Distributor Caps and Rotors

What a Technician needs to know when diagnosing faults for condensers and contact points on early points distributor systems and distributor caps and rotors on all points and electronic distributor systems.

We all know that the points distributor system numbers have been reducing over the past years, but it is still important to ensure that they are diagnosed, tested and repaired correctly when a vehicle with this system visits your workshop.

Important features of the points type system.

  • Most systems are negative Earth, but some very early English manufactured systems were positive Earth. (need to get this right)
  • The system will generally incorporate a ballast resistor in the primary circuit to reduce the voltage supply to the Ignition coil and circuit. This is necessary as the Ignition coils on these systems operate on a lower voltage than battery 12V. (e.g. 8V). A ballast resistor by-pass circuit during “cranking only” allows for a higher full battery voltage to be supplied to the ignition coil which results in a greater spark output for easier starting. The reduced/lower running voltage and current flow is enough to operate the ignition system (after engine start) reducing the premature ignition failure due to any higher voltage and current flow in the circuit. Discoloured and burnt contact points generally indicate that the current flow has been excessive in the primary circuit (low voltage circuit) or a faulty condenser. An Ignition coil that is rated and stamped as 12V should not be fitted to a points system that utilises a ballast resistor. (A 12V ignition coil is generally used on electronic ignition systems).

Typical points system Primary circuit

  • The condenser is utilised in parallel circuit to reduce arcing across the ignition contact points as they open to induce the ignition coil HT spark. A faulty condenser generally results in a nil or hard start and poor running condition causing premature contact point failure. Note: Not all capacitors are the same. They are rated in their ability to store energy which is generally stamped on the housing. The rating in microfarads (unit of capacitance) must match the ignition system it is fitted to. Replacement with another rating can cause ignition malfunctions. Fitting an incorrect ignition coil may also cause premature ignition failure. Contact points that are badly pitted is generally a sign that the condenser or Earth needs to be investigated closely.
  • It is important that the distributor shaft cam has not worn excessively over time as this will affect contact point and dwell function. Ensuring the contact point gap is accurately set with a dwell meter to manufacturers specifications allows for correct coil operation. (adjusting air gap with feeler gauge is not as accurate as the dwell meter method especially on contact points that have been fitted for some time).

Lubricating the CAM and rubbing block will ensure that the contact point gap will not reduce quickly due to wear of the rubbing block during operation. The reduced gap can create a hard start condition and excessive dwell that can cause damage to the ignition coil.

Important features for Distributor caps and rotors.

All distributors whether contact type or electronic, require an internal rotor and a distributor cap to ensure the high voltage / HT spark created by the ignition coil be distributed to the correct cylinder without the spark tracking to ground or any unwanted area.

The voltages on later electronic distributors are generally extremely high and many utilise male spark towers to reduce any unwanted tracking of the spark during peak voltage - High load / hard acceleration.  Achieving full HT spark to the spark plugs will generally reduce the chance of engine misfiring.

It is important that the condition of both distributor caps and rotors are closely checked for any tracking signs prior to replacing any other ignition component.

Note: Di-Electric grease/paste is generally used on the distributor cap tower to form a seal for the HT leads to prevent moisture creating a spark track that can cause engine misfiring. This paste also allows for easier removal of the HT leads later without HT lead damage.

The Premier Auto Trade Ignition range includes hundreds of secondary ignition products from the world’s leading manufacturers, covering millions of vehicle applications in Australia and NZ.

When you supply and fit products from Premier Auto Trade you can expect a product designed and tested to the vehicle manufacturer’s specifications offering OE form, fit and function. Premier Auto Trade distributes products throughout Australia via a network of specialised resellers and leading automotive groups.

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