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 spark plugs. To do this, the coil depends on the points and 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 on to 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 is interrupted. The magnetic field in the primary circuit of the coil collapses and cuts through the secondary circuit windings around the iron core. Because of the scientific phenomenon called electromagnetic induction, the battery voltage is at this point 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 opened contacts of the points. If this charge were not transferred elsewhere, the metal contacts of the points would melt to change rapidly. If the 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.
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 the 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. Changing the ignition timing, however, does not affect the dwell of the breaker points.REMOVAL & INSTALLATION
- Snap off the two spring clips that hold the distributor cap to the distributor. Remove the cap and examine it for cracks, deterioration, or carbon tracking. Replace the cap if necessary; transfer one wire at a time from the old cap to the new one. Examine the rotor for corrosion or wear and replace it if it's at all questionable.
- Turn the engine with the crankshaft pulley until the rubbing block on the points is on the high point of the distributor cam. (Rotor removed).
- Observe which screws retain the ground and primary wires. Remove the two retaining screws.
We suggest a magnetic screwdriver, a screw start or some kind of screw holding device so you will not drop the retaining screws into the distributor or onto the ground.
- Remove the distributor breaker points.
- Install the new set of points; make sure that the pin on the bottom of the points engages the hole in the breaker plate.
- Install the lubricator wick primary and ground wires and two retaining screws. Tighten the screws slightly snug.
- Check to be sure that the rubbing block on the points is on the high part of the distributor cam.
- On 1971-74 models, gap adjustment is made by turning the eccentric screw in or out as necessary to bring it within specs. On 1975 and later models, point adjustment is made by using a screwdriver in the slot provided and pivoting it to open or close the gap. Refer to the underhood decal or the Tune-Up specifications in this section for the correct point setting.
- When the gap is correct, tighten the retaining screws.
- Install the rotor and distributor cap.
- The condenser is mounted on the outside of the distributor. Undo the mounting screw and the terminal screw or slide connector to replace the condenser.
- Adjust the points with a feeler gauge as described.
- Follow the directions that come with the dwell meter and connect it to your ignition circuit. One lead of the meter is connected to a ground and the other lead is to be connected to the distributor post on the coil. An adapter is usually provided for this purpose.
- If the dwell meter has a zero set adjustment on it, make sure to zero the meter.
- Start the engine and allow it to idle.
- Observe the reading on the dwell meter. If the reading is within the specified range, turn OFF the engine and remove the dwell meter.
- If the reading is above the specified range, the breaker point gap is too small. If the reading is below the specified range, the gap is too large. In either case, the engine must be stopped and the gap adjusted. After making the adjustment, start the engine and recheck the reading on the dwell meter. When the correct reading is obtained, disconnect the dwell meter.
- Check and adjust the ignition timing.