The earliest timed spark ignitions used a spring loaded mechanical switch actuated by a cam. The cam forces the switch open and the spring closes it again. The switch connects the negative lead of the ignition coil primary to ground. When the switch is closed, current flows through the primary. When the points of the switch separate, they break the circuit [Im guessing that is why they are called breaker points, or points]. An engine will typically have one set of points but there may be multiple points hooked to multiple coils or even two sets of points hooked to one coil. When you have two sets of points on one coil it is called a dual point system. If there is only one set of points per coil then it is a single point system. Even if there are multiple coils, each with one set of points, then it is still single point.
    Points are the simplest ignition system since the points are both the sensor and actuator. All you need to make a spark is a battery, a coil, and the points. Oh, and a condenser but well talk more about that later. There are two types of points ignitions, battery powered and magneto. They function exactly the same; close points so current flows through primary then open points to fire coil. A battery powered ignition connects the coil primary to the battery for current. A magneto runs a magnet past the primary to generate a current inside the coil. On this page Ill be talking about battery powered ignitions but the concepts are the same for magnetos.

Setup
    Before we get in depth on the workings of a points system, you first need to know how to set one up. For points to work properly the mechanical assembly has to be in good shape. Lube everything up and check for wear. If anything is sloppy or binding then you won't get a stable dwell. A little slop is not OK. Everything must be like new for the assembly to work properly. If any of your shafts, bushings, or plates show any wear then stop reading now and find replacement parts before continuing. All shafts, bushings, and pivots need to be lubed with light oil. Dont just squirt it with WD40 or any other oil that will quickly evaporate. I use spindle oil but motor oil will work. The breaker cam must be lubed with grease that wont fly off when its spinning. Dont even think about using motor oil on the cam. You can buy grease specially made for breaker cams but its getting harder to find. Camshaft assembly lube works well also. To make the points last longer between adjustments you should polish the breaker cam. The cam surface needs to be smooth. Any rust or gunk built up on the cam will grind away the rubbing block on the points. A fine emery cloth or Scotch Brite pad works well for getting the cam surface back to shiny metal. One thing most people don't consider when installing new points is the contact area. The two contacts should hit dead center, see picture. To align the contacts, bend the stationary breaker point bracket. Do NOT bend the breaker arm. You should also check the breaker arm spring tension, a 2 or 3 pound pocket fishing scale works well for this. Spring tension is usually 16-32 ounces depending on the application. A low rpm motor can get by with 16-20 ounces where a high rpm motor may need as much as 32 ounces to keep the points from bouncing. Higher spring tension increases the rpm range but also wears down the breaker arm rubbing block faster. If you don't rev your motor very high then lower the spring tension and your points will last a lot longer. Next you should set the gap with a feeler gauge to get it running. Turn the motor over until the points rubbing block is on the highest point of the breaker cam. At this point you will have the widest gap between the points. Check the specs for your system to find out what the gap should be. If you dont know what the spec is, then set them at .015 which is close enough for most systems. You need to develop a feel for adjusting the gap. Its easy to jam a thick feeler gauge into a narrow gap because the points are spring loaded. You want to adjust it so there is an ever so slight drag. This is even more difficult with a blade type gauge which if turned or tilted even slightly will make it feel like the gap is too small. A wire type gauge makes adjustment easier. The point gap effects the dwell (the amount of time current is running through the coil). The feeler gauge setting is only to get it close enough to run. When the motor is running, you can fine tune it with a dwell meter. The dwell spec is usually given as an angle. What that represents is the degrees the point cam rotates between when the points close and when they open again. A dwell meter will have a different scale for the different engine configurations. The 8 cylinder scale reads 0-45, the 6 cylinder scale reads 0-60, and the 4 cylinder scale reads 0-90. An automotive dwell meter can be used on a motorcycle too if you know what the meter is actually reading. The meter is only measuring duty cycle, the percentage of time that the points are closed. A 27 dwell on an 8 cylinder is a duty cycle of 60% (27/45). If your bike has only one lump on the cam then it fires once every 360. If the dwell spec is 90 then the duty cycle is 25% (90/360). So using the 6 cylinder scale you would set it to 15 (0.25*60). Once it is all set up, break-in the new points for a couple days, then recheck everything and make any necessary adjustments.

Pros
    The biggest advantage point systems have is their simplicity. There are very few components and its mostly mechanical so you can see how everything works. Its easy to wire up and the engine looks clean without extra wires and boxes. Rarely will a points ignition leave you stranded looking for parts. It most cases you can scratch the points clean with a pocket knife and gap them with a matchbook and be on your way. Since there are no electronics, a points system is not affected by electrical interference. You can run solid core plug wires and the engine wont miss a beat.

Cons
    The mechanical design of points also works to its disadvantage. When the breaker cam opens the points at high rpm, the inertia in the breaker arm will keep the points opening after reaching the high spot on the cam. Rather than riding down the back side of the cam and closing smoothly they will slam shut and even bounce. This is called point float or point bounce. Point bounce will wear out a set of points quickly and can cause the ignition to misfire. There has to be adequate spring tension to prevent the points from floating. It is this spring tension that wears out the rubbing block and causes the point gap to close up with use. Points need to be adjusted periodically to account for this wear. That is the single biggest reason for people to be either a point lover or a point hater. Some people despise having to always be working on it while others enjoy the ritual as part of the pleasure of keeping an old machine on the road.
    The cam needs to open the points gradually to prevent float. This causes a big problem when it comes to breaking the primary circuit. Think of the points as a little 4 amp arc welder. When arc welding, you touch the electrode to your work piece, to start current flowing, and lift it up to get an arc gap. The constant current power source of the arc welder will increase the voltage to the electrode to maintain the current flow across the arc. If you keep lifting the electrode you will reach a point where the welder can not supply enough voltage to maintain the arc and current flow will stop. Points will do the exact same thing. Current flows through them when they close. When they open the inductance of the ignition coil tries to maintain that current so an arc will be struck between them until the points open up enough to break the circuit. The more current you run through the points, the harder it is for them to break the current. That is why point systems have a condenser (called a capacitor in any other electrical system). The condenser slows down the reaction time of the coil to allow the points time to open and break the circuit. Without a condenser you will likely never break the primary current and get no spark from the secondary. Having a condenser that is too large will completely prevent arcing across the points but will also slow the coil so much that it is unable to strike an arc on the secondary. The trick is to find a condenser that gives a happy medium between the arc at the points and the arc at the spark plug. A smaller condenser means more power from the coil but shorter point life due to pitting. A larger condenser will give you longer point life but sacrifice coil output. One trick to make a high performance points system is to wire two condensers together in series. This effectively gives you one condenser with half the value. Most guys when changing points will replace the condenser if it needs it or not. This is not always a good idea. A condenser is a simple component and they rarely go bad. The only bad condenser I've seen was brand new, the wire had broken off inside. If you are changing your points and the motor was running fine then do not replace your condenser. You may do more harm than good.
    Another disadvantage to points is the dwell strategy. The dwell of a points system is a fixed duty cycle. On a V8 the points open every 45. With the dwell set to 30 the duty cycle is 66.67%. That means that regardless of engine speed, there will be current flowing through the primary of the coil two thirds of the time. This chart illustrates why this is not a desirable dwell strategy. In this example it takes the coil 2.5 milliseconds to charge. The charge time of the coil is constant. Whether the engine is spinning fast or slow, it will take 2.5 milliseconds to charge the coil. At 1000 rpm the points are closed for 10 milliseconds. After 2.5 millisecond the coil is fully charged (illustrated by the dark blue line), but energy is put through the primary for an additional 7.5 milliseconds (light blue line). That energy is wasted heating up the coil. Points systems use a ballast resistor and/or high resistance coil to limit the peak current so the coil wont burn up. That high resistance slows down the charge rate of the coil and limits the energy it can store. The pink line shows the energy put into and stored in the coil at 5000 rpm. Because the duty cycle is fixed, and because of the high primary resistance, the dwell is not long enough to fully charge the coil. If you were setting up the ignition on a generator or lawn mower where the engine ran at a constant speed then you could set the dwell to charge the coil completely without wasting energy. However, the engine in a car does not run at a constant speed so the dwell of points is almost never correct. The coil is either burning up because it was charged too long or crapping out because it wasnt charged long enough.

Dual Points
    Dual point distributors were used on high performance engines back in the day before electronic ignitions. A dual point system has two sets of points, slightly offset, driving one coil. The purpose of the dual points is to increase the dwell and allow wider point gaps. A standard Ford single point distributor has about 28 dwell with a .014" point gap. A Ford dual point has 33 with a .019" gap. The longer dwell allowed the ignition to operate at higher rpm because it gave the coil more time to charge. The wider point gap allowed it to more easily break the primary current. Since a dual point has larger point gaps it also needs higher breaker spring tension. The factory spec for a Ford dual point is 27-30 ounces.
    Adjusting a dual point is a little different than single points. You need to isolate one set of points at a time to make sure they are both set to the same dwell. You also need to make sure the combined dwell is within spec. My uncle showed me a great way to adjust a dual point distributor. Hook a remote start switch to the starter solenoid and a dwell meter to the distributor. Pull the coil lead off the distributor cap and ground it to the motor. Pull off the distributor cap and rotor so you can get to the points. Place a thin piece of cardboard or plastic between one set of points so they don't make contact. Turn the motor over with the remote start switch (make sure the car is out of gear first) and read the dwell. Then move the cardboard to the other points and measure the dwell again. Adjust the points as needed until both are the same when isolated and give you the proper total dwell when combined. I adjust mine to 26 each which gave me a total of 33.
    Dual points were a good idea back when there was no better alternative. They provide slightly better performance than a single point system but suffer from all the same shortcomings. These days, electronic ignitions are cheaper and simpler than dual points and will perform much better. Single points can still be desirable in a non-performance application because they are simple and dependable, but dual points is system whose time has come and gone.

    For those of you who are anti-point and feel I'm wasting web space for even mentioning them, please send hate mail to mrriggs@gofastforless.com. The rest of you, who still know a good thing when you see it, write me at mrriggs@gofastforless.com and let me know what you think.

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