See Figures 1 and 2
All 1971-1973, and some 1974 Ford full sized cars used a breaker point type ignition system.
The points function as a circuit breaker for the primary circuit of the ignition system. The ignition coil must boost the 1 volts of electrical current supplied by the battery to as much as 25,000 volts in order to properly fire the spark 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 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 collapses. The magnetic field in the primary circuit of the coil cuts through the secondary circuit winding 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 is not transferred elsewhere, the metal contacts of the points would melt and the gap would start to change rapidly. Without the proper gap, the points will be unable to break the primary circuit, and the end result will be 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
prevent the points from becoming pitted or burned.
It is interesting to note that the cycle must be completed by the ignition system every time a spark plug fires. In a V8 engine, all of the spark plugs fire once for every two revolutions of the crankshaft. That means that in one revolution, four spark plugs fire. So when the engine is at an idle speed of 800 rpm, the points are opening and closing 3,90 times a minute.
There are two ways to inspect the breaker point gap: it can be checked with a feeler gauge, or a dwell meter. In either way, when 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 level at which 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 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 to check the ignition timing. If the point gap or dwell is changed, the ignition timing must be checked and adjusted as needed.
See Figure 3
- Disconnect the negative battery cable.
- Disconnect the high tension wire from the top of the distributor and the coil.
- Remove the distributor cap by prying off the spring clips on the sides of the cap.
- Remove the rotor from the distributor shaft by pulling it straight up. Examine the condition of the rotor. If it is cracked or the metal tip is excessively worn, it should be replaced.
- Pry open the contacts of the points with a small prytool and check the condition of the contacts. If they are excessively worn, burned or pitted, they should be replaced.
- Inspect the condition of the condenser. If the wire insulation is cracked or burnt, replace the unit.
- If the points and condenser are in good condition, adjust them, and install the rotor and the distributor cap. If the points need to be replaced, follow the replacement procedure given below.
See Figures 4 through 10
- Disconnect the negative battery cable.
- Remove the coil high tension wire from the top of the distributor cap. Remove the cap from the distributor and place it out of the way. Remove the rotor from the distributor shaft.
- Loosen the screw that holds the condenser lead to the body of the breaker points, then disconnect the lead.
- Remove the screw that holds and grounds the condenser to the distributor body. Remove the condenser from the distributor and discard it.
- Unfasten the points assembly attaching screws and adjustment lockscrews. A screwdriver with a magnetic tip will come in handy here so you don't drop a screw into the distributor and have to remove the entire assembly to retrieve it.
- Remove the points. Wipe off the cam and apply new cam lubricant. Discard the old point set.
- Position the new set of points with the locating peg in the hole on the breaker plate, and install the screws that hold the assembly onto the plate. Do not tighten them all the way.
- Attach the new condenser to the plate with the ground screw.
- Attach the condenser lead to the points.
- Apply a small amount of cam lubricant to the shaft where the rubbing block of the points touches.
- Attach the negative battery cable.