Previous Next

POINT TYPE IGNITION SYSTEM

Breaker Points and Condenser

OPERATION

NOTE: Point type ignition was used through the 1978 model year. The following information applies only to these model years. Beginning in 1979, electronic ignition became standard equipment. Testing and adjustments on 1979 and later models is given a little later in this chapter.

The points function as a circuit breaker for the primary circuit of the ignition system. The ignition coil must boost the 12 volts of electrical pressure supplied by the battery to as much as 25,000 volts in order to fire the plugs. To do this, the coil depends on the points and the condenser to make a clean break in the primary circuit.

The coil has both primary and secondary circuits. When the ignition is turned on, the battery supplies voltage through the coil and onto the points. The points are connected to ground, completing the primary circuit. As the current passes through the coil, a magnetic field is created in the iron center core of the coil. As the cam in the distributor turns, the points open and the primary circuit collapses. The magnetic field in the primary circuit of the coil also collapses and cuts through the secondary circuit windings around the iron core. Because of the scientific phenomenon called electromagnetic induction, the battery voltage is increased to a level sufficient to fire the spark plugs.

When the points open, the electrical charge in the primary circuit jumps the gap created between the two open contacts of the points. If this electrical charge were not transferred elsewhere, the metal contacts of the points would melt and the gap between the points would start to change rapidly. If this gap is not maintained, the points will not break the primary circuit. If the primary circuit is not broken, the secondary circuit will not have enough voltage to fire the spark plugs.

The function of the condenser is to absorb excessive voltage from the points when they open and thus prevent the points from becoming pitted or burned.

It is interesting to note that the above cycle must be completed by the ignition system every time a spark plug fires.

There are two ways to check the breaker point gap. It can be done with a feeler gauge or a dwell meter. Either way you set the points, you are basically adjusting the amount of time that the points remain open. The time is measured in degrees of distributor rotation. When you measure the gap between the breaker points with a feeler gauge, you are setting the maximum amount the points will open when the rubbing block on the points is on a high point of the distributor cam. When you adjust the points with a dwell meter, you are adjusting the number of degrees that the points will remain closed before they start to open as a high point of the distributor cam approaches the rubbing block of the points.

When you replace a set of points, always replace the condenser at the same time.

When you change the point gap or dwell, you will also have changed the ignition timing. So, if the point gap or dwell is changed, the ignition timing must be adjusted also.

Previous Next