The points function as a circuit breaker for the primary circuit of the ignition system. The ignition coil must boost the 12 volts 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. When the cam in the distributor turns, the points open, breaking the primary circuit. The magnetic field in the primary circuit of the coil then collapses and cuts through the secondary circuit windings around the iron core. Because of the physical principle 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 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 change 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.
If you have ever wondered why it is necessary to tune-up your engine occasionally, consider the fact that the ignition system must complete the above cycle each time a spark plug fires. On a four-cylinder, four-cycle engine, two of the four plugs must fire once for every engine revolution. If the idle speed of your engine is 800 revolutions per minute (800 rpm), the breaker points open and close two times for each revolution. For every minute your engine idles, your points open and close 1,600 times (2×800=1,600). And that is just at idle. What about at 60 mph-
There are two ways 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 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 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.
If you still do not understand how the points function, take a friend, go outside, and remove the distributor cap from your engine. Have your friend operate the starter (make sure that the transmission is not in gear) as you look at the exposed parts of the distributor.
There are two rules that should always be followed when adjusting or replacing points. The points and condenser are a matched set; never replace one without replacing the other. If you change the 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.
REMOVAL & INSTALLATION
See Figures 1, 2, 3, 4 and 5
The usual procedure is to replace the condenser each time the point set is replaced. Although this is not always necessary, it is easy to do at this time and the cost is negligible. Every time you adjust or replace the breaker points, the ignition timing must be checked and, if necessary, adjusted. No special equipment other than a feeler gauge is required for point replacement or adjustment, but a dwell meter is strongly advised. A magnetic screwdriver is handy to prevent the small points and condenser screws from falling down into the distributor.
Point sets using the push-in type wiring terminal should be used on those distributors equipped with an R.F.I. (Radio Frequency Interference) shield (1970-74). Points using a lockscrew-type terminal may short out due to contact between the shield and the screw.
- Push down on the spring-loaded distributor cap retaining screws and give them a half-turn to release. Remove the cap. You might have to unclip or detach some or all of the plug wires to remove the cap. If so, number the wires and the cap for removal.
- Clean the cap inside and out with a clean rag. Check for cracks and carbon paths. A carbon path shows up as a dark line, usually from one of the cap sockets or inside terminals to a ground. Check the condition of the carbon button inside the center of the cap and the inside terminals. Replace the cap as necessary. Carbon paths cannot usually be successfully scraped off. It is better to replace the cap.
- Remove the two screws and lift the round rotor off. There is less danger of losing the screws if you just back them out all the way and lift them off with the rotor. Clean off the metal outer tip if it is burned or corroded. Don't file it. Replace the rotor as necessary or if one came with your tune-up kit.
- Remove the radio frequency interference shield if your distributor has one. Watch out for those little screws! The factory says that the points don't need to be replaced if they are only slightly rough or pitted. However, sad experience shows that it is more economical and reliable in the long run to replace the point set while the distributor is open, then to have to do this at a later (and possible more inconvenient) time.
- Pull off the two wire terminals from the point assembly. One wire comes from the condenser and the other comes from within the distributor. The terminals are usually held in place by spring tension only. There might be a clamp screw securing the terminals on some older versions. There is also available a one-piece point/condenser assembly. The radio frequency interference shield isn't needed with this set. Loosen the point set hold-down screw(s). Be very careful not to drop any of these little screws inside the distributor. If this happens, the distributor will probably have to be removed to get at the screw. If the hold-down screw is lost elsewhere, it must be replaced with one that is no longer than the original to avoid interference with the distributor workings. Remove the point set, even if it is to be reused.
- If the points are to be reused, clean them with a few strokes of special point file. This is done with the points removed to prevent tiny metal filings from getting into the distributor. Don't use sandpaper or emery cloth; they will cause rapid point burning.
- Loosen the condenser hold-down screw and slide the condenser out of the clamp. This will save you a struggle with the clamp, condenser, and the tiny screw when you install the new one. If you have the type of clamp that is permanently fastened to the condenser, remove the screw and the condenser. Don't lose the screw.
- Attend to the distributor cam lubricator. If you have the round kind, turn it around on its shaft at the first tune-up and replace it at the second. If you have the long kind, switch ends at the first tune-up and replace it at the second.
Don't oil or grease the lubricator. The foam is impregnated with a special lubricant.
If you didn't get any lubricator at all, or if it looks like someone took it off, don't worry. You don't really need it. Just rub a matchhead size dab of grease on the cam lobes.
- Install the new condenser. If you left the clamp in place, just slide the new condenser into the clamp.
- Replace the point set and tighten the screws. Replace the two wire terminals, making sure that the wires don't interfere with anything. Some distributors have a ground wire that must go under one of the screws.
- Check that the contacts meet squarely. If they don't, bend the tab supporting the fixed contact.
- Turn the engine until a high point on the cam that opens the points contacts the rubbing block on the point arm. You can turn the engine by hand if you can get a wrench on the crankshaft pulley nut, or you can grasp the fan belt and turn the engine with the spark plugs removed.
Another alternative is to bump the starter switch or use a remote starter switch.
- On the V8 engine, simply insert a 1 / 8 in. allen wrench into the adjustment screw and turn. The wrench sometimes comes with a tune-up kit.
- Insert the correct size feeler gauge and adjust the gap until you can push the gauge in and out between the contacts with a slight drag, but without disturbing the point arm. This operation takes a bit of experience to obtain the correct feel. Check by trying the gauges 0.001-0.002 in. (0.025-0.050mm) larger and smaller than the setting size. The larger one should disturb the point arm, while the smaller one should not drag at all. Recheck the gap, because if often changes when the screw is tightened.
- After all the point adjustments are complete, pull a white index card through (between) the contacts to remove any traces of oil. Oil will cause rapid contact burning.
- Replace the radio frequency interference shield, if any. You don't need it if you are installing the one-piece point/condenser set. Push the rotor firmly down into place. It will only go on one way. Tighten rotor screws. If the rotor is not installed properly, it will probably break when the starter is operated.
- Replace the distributor cap.
- If a dwell meter is available, check the dwell.
This hookup may not apply to electronic, capacitive discharge, or other special ignition systems. Some dwell meters won't work at all with such systems.
These engines use the breakerless HEI (High Energy Ignition) system. Since there is no mechanical contact, there is no wear or need for periodic service. There is an item in the distributor that resembles a condenser; it is a radio interference suppression capacitor which requires no service.