How Do You Know if Your Points Are Bad
Understanding Breaker Point Ignition Systems
By Staff
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Figure 1: Ignition points must lineup correctly when they are closed. If they don't shut (left), or aren't aligned (center), the organization won't work.
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Figure 2: Test resistance of coil with multi-meter set on Ohms. Test battery ground connection with a multi-meter assault volts D.C.
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Effigy iii: Testing for a curt at the points with a multi-meter set on continuity. Testing the ignition switch with a multi-meter set on volts D.C. Meter should show 12 to 13 volts.
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Breaker point ignition systems were, until the advent of electronic ignition systems, used on millions of engines. From the engines powering rum runners of the 1930s to all those Jeeps in World War Ii, all of them had breaker bespeak ignition systems. Simple to troubleshoot and repair, they are, like anything else, infinitely complex if you don't understand the basics of how they work.
Billow Point Basics
The breaker point ignition arrangement circuit starts and ends with the bombardment. When the engine is running the battery is continuously being recharged by an alternator or, on older systems, a generator. Electric current flows from the positive terminal of the bombardment to the ignition switch and an ignition coil. The ignition roll is actually a transformer that steps up the 12-volt current of the bombardment to somewhere in the neighborhood of 25,000 volts. In engines of medium to high compression this kind of voltage is necessary to reliably arc across the gap on a spark plug and make plenty fire to ignite the fuel/air mixture in a cylinder.
The coil has ii circuits in it; the primary, which runs from the positive gyre terminal to the negative scroll terminal; and the secondary excursion, which goes from the positive final on the coil to the ignition wire in the centre of the distributor cap. The negative wire on the principal circuit runs from the coil to the base of operations of the distributor and the breaker points within. This may sound a footling confusing, merely it makes sense when you lot sympathize that the points act to open and shut the basis circuit.
The breaker points open and close as the distributor shaft rotates. 1 one-half of the betoken ready is stock-still, the other half pivots and there is a rubbing cake on the moveable half of the point set up. The benefactor shaft has lobes that contact the rubbing block. These lobes act as cams to push the points open, thereby breaking the electrical connexion betwixt the points. The points accept a spring clip that acts to hold the points shut, and this spring causes the moveable point to snap back into contact with the stationary point mounted to the distributor plate when the cam rotates out of contact. If this is unclear, accept the distributor cap off of a breaker indicate-equipped engine and rotate the engine manually, watching the parts movement. The interplay will go obvious.
The spring prune is electrically insulated from the distributor torso then that the primary circuit is grounded only when the points are airtight. When the points are touching each other electricity runs from the bombardment, through the coil and to the engine cake, which is grounded to the negative final on the bombardment. The current running through the windings in the ignition scroll builds upward a powerful electric field that is unleashed when the points separate. No longer able to go to basis through the points, the electricity, which is seeking the easiest path to footing, rushes through the secondary circuit to the coil wire to the top of the distributor cap where it is transmitted to the distributor rotor.
The rotor is fixed to the top of the distributor shaft and revolves around the inside of the distributor, its contact giving each post on the circumference of the distributor cap a shot of electricity as it passes past. The posts have wires attached to them and these atomic number 82 to the spark plugs that ignite the fuel/air mixture in the cylinder.
The spark has to be timed so that it sets off the gas at the correct part of the piston bicycle, usually when the piston is near the acme of the cylinder. On most engines ignition timing is ready by loosening a distributor hold down bolt and rotating the benefactor to accelerate or retard the spark timing. Old-time garage jockeys used to set timing by ear, turning the benefactor until the engine sounded "right." Most mechanics utilise a timing light that takes a signal from a spark plug wire and releases a pulse of light every time the spark plug wire has electricity running through it. The light is aimed at one of the pulleys on the front of the engine and the benefactor is rotated until a notch on the pulley lines up with a mark on the caster baby-sit.
Troubleshooting
Knowing how a breaker point organisation works puts yous in a much better position to repair it when information technology breaks downward. If your engine isn't running and you suspect the ignition system, the first affair to practice is look the whole affair over for annihilation that is patently wrong, like loose or cleaved wires.
Push down hard on the boots at the terminate of the spark plug wires to brand sure that they are on securely. Take a glance at the points; if they look corroded replace them. Check the gap between the points (the space formed when the points are at their widest open setting) with a feeler gauge, getting the proper specification for the gap from a repair manual. A typical setting is 0.015- to 0.020-inch. Employ a socket and a breaker bar to rotate the engine so that the points are at their widest gap. The gauge, either a wire blazon or feeler type, should but slide betwixt the points without pushing them apart.
If this doesn't solve the problem, effort tracing the entire circuit, starting with the battery. Test the battery with a voltmeter and a hydrometer. You lot want the battery to read at least 12.6 volts, assuming yous take a 12-volt organisation. If the bombardment needs to be recharged make sure to employ a trickle charger, a charger that runs at no more than 2 amps. High amp chargers tin can ruin a battery if used often,, something I had to learn the hard way.
Double-check the bombardment with a hydrometer.
Be sure to wear splash-proof goggles. Each cell should read almost the same as the others. If you become a drastically different reading in one prison cell y'all may have a bad battery.
Use the voltmeter to have a reading at the ends of the battery cables. The voltage should be the aforementioned every bit at the battery itself. If not, clean the ends of the cables and endeavour over again. If you nevertheless become a voltage drop at the end of the cables, junk them and get new cables. While you are at it, try fluctuant the cables around with the voltmeter probes firmly fastened. If yous run into a low or nonexistent reading yous accept a cable that is corroded on the within.
Bold you have a good battery that is fully charged, skillful bombardment cables and clean, tight connections you can start testing other parts of the circuit. Place the positive probe of the test meter on the positive bombardment concluding and the negative probe on a make clean part of the engine block. This tests the ground connectedness between the negative battery concluding and the block. If the voltmeter reads lower than the battery you need to clean and/or tighten the ground connection.
You can go through the whole circuit testing the voltage at each wire and component. If yous notice a significant drop in voltage, end to bank check for a bad connection or wire. Some engines accept an external resistor near the ignition coil. This will affect the voltage reading you get according to the strength of the resistor.
You can check the resistor with an ohmmeter. Go the resistance of the resistor from the transmission for your engine (some resistors may have their ohm rating marked on them). The whorl tin can exist checked the same style.
Use your voltmeter to check for a brusque to footing betwixt the battery and the points. Block the points open with a small piece of wood and put one probe on the appropriate bombardment terminal and the other probe on the point itself. Only brand certain that you lot have your polarities straight. With the points blocked open 1 will be positive, the other negative. If the meter doesn't show whatsoever voltage when the probe is on the "spring prune," you may have a bad insulating washer at the distributor, which would let electricity become to ground through the block before going to the points. Examination for continuity between the block and the negative gyre concluding to confirm this theory. Examination for continuity between the block and the stationary point attached to the distributor plate.
Rotate the engine until the points are closed. Use the multi-meter to test for a good connection between the points. A slight gap when the points are supposed to be closed will continue your machine from running.
If you do not accept a examination meter you can use a cocky-powered examination calorie-free to do essentially the aforementioned thing. Ever apply the examination light with the battery disconnected. When the circuit is airtight the light will smoothen. If you take a fault in the circuit, such as a broken wire, the light will not come on.
Starting at the battery cables go around the circuit testing each wire and connection. Cake the points open and identify each probe on 1 of the points. If the calorie-free goes on yous have found the problem. Look carefully to notice the bare patch of insulation or missing safety washer on the distributor wire.
With the points touching and the probes on each point the light should shine for you. If the calorie-free doesn't become on they aren't really touching or they are so corroded that they won't comport electricity. Yous tin file them downwardly, or amend yet supervene upon them. Information technology is a good idea to supplant the point condenser at the same time. The condenser is usually located within the distributor, only sometimes is fastened to the outside housing. It has a single lead that attaches to the points where the negative wire from the ignition coil attaches.
If you're nonetheless non having any luck, try checking the resistance of the spark plug wires. I know a lot of u.s. detest manuals, but it'due south good to have the specs for your slice of iron and so you lot tin test these things out. Any spark plugs wires with cracked insulation should be replaced.
Apply your multi-meter to examination the spark plugs. At that place should exist continuity between the top of the plug and the electrode. There shouldn't be whatsoever continuity between the screw threads and the electrode. Put the end of the plug in the boot on the cease of the ignition wire and test for continuity between the electrode and the end of the plug wire. This will rule out a bad plug wire or a bad connection between plug and wire.
If you have gone through all of this and nonetheless can't get any spark have a look at the cap and rotor. These are ordinarily the starting time parts that get replaced when someone is going over the ignition system. If they look onetime or damaged, I would supercede them.
After going through all of this you should take a expert feel for how your breaker bespeak ignition system works, and how to work your way through when y'all're having ignition-related problems. Understanding how the organization works is fundamental, and if you lot have your time and trace the organization downward, you'll always find your way to making it work.
Contact engine enthusiast Gary Grinnell at: 9 Laurel Park, Northampton, MA 01060-1196.
Published on Oct i, 2002
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How Do You Know if Your Points Are Bad
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