Volkswagen Front Wheel Drive 1974-1989 Repair Guide

Description & Operation


See Figures 1 and 2

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; which 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. When the cam in the distributor turns, the points open, breaking the primary circuit of the coil which then collapses and cuts through the secondary circuit windings around the iron core. Due to electromagnetic induction, the battery voltage is increased to a level sufficient to fire the spark plugs.

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Fig. Fig. 1: Components in a point type ignition distributor

When the points open, the electrical charge in the primary circuit tries to jump 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 start to wear rapidly. 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.

There are two ways to check to check breaker point gap: with a feeler gauge or with a dwell meter. Either way you set the points, you are adjusting the amount of time (in degrees of distributor rotation) that the points will remain open. If you adjust the points with a feeler gauge, you are setting the maximum amount the points will open when the rubber block on the points is on a high point of the distributor cam. When you adjust the points with a dwell meter, you are measuring the number of degrees (of distributor cam rotation) 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.

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Fig. Fig. 2: Dwell angle

There are two rules that should always be followed when adjusting or replacing the points. The points and condenser are a matched set; never replace one without replacing the other. If you change point gap or dwell of the engine, you also change the ignition timing. Therefore, if you adjust the points, you must also adjust the timing.