To help you get a better understanding of magnetism...
Point’s are means of interrupting the current to cause the rise and fall of the magnetic field is a set of normally closed points that respond to the magnetism in the core. When the points open and discharge the field of voltage and the points close then the process is repeated. The first magnet on the flywheel is the North pole it passes the first leg of the coil then passes to the center leg the south pole magnet shows up at the first leg and this is where the primary coil windings begins to set up it’s field of magnetism when the North pole magnet enters the last leg then the south pole magnet arrives at the center leg and this sets up the secondary winding for maximum fire power.
The magnetic field is now flowing in a circle around each side of the coil (which is on the center leg) and the two outer legs form a circle of magnetism and enters in through the center laminations that the coil is mounted on inducing a field for the secondary coil windings to generate the required voltage to send to the spark plug. When the South pole magnet shows up at the center leg and the North pole magnet is on the last leg it’s completing the field then the points open at the correct Before Top Dead Center settings to fire the motor combustion chamber…
A capacitor or condenser is used across the contacts to aid in the rapid field collapse and to reduce contact arcing thus extending the life of the points. (The condenser absorbs the self-induced current of the primary winding, preventing it from opposing the rapid fall of the primary current.) Early condenser’s were made up by alternating layers of tin foil and paraffined paper, cut to the same size, like the pages of a book. Even numbered foil sheets were connected together for one polarity and odd numbered sheets were connected together for the opposite polarity. These connections were then routed to each side of the breaker points. But that is the old school way from way back when. The newer condensers made in a more updated and that tin foil set up is still used but put in a round cylinder with one lead coming out of it going to where the point’s wiring is hooked up…
So, here's how it is the points and the condenser and one of the little wires from the coil is grounded usually near the laminated plate area and this all ground s through the engine block. The engine block is actually part of the magnetic field that is set up. The positive flow of electrons has to flow to a negative even though we have north and south pole magnets that positive energy has to flow in one direction only and that is through the coil wire to ground when the points calls for a spark, initial current flows in one direction and saturates the laminations. The moving points are then pulled open and the coil discharges. Meanwhile, a SECONDARY winding made up of a great many more turns of finer wire has picked up the rapidly collapsing magnetic field. More turns means more voltage and this voltage is then delivered via an INSULATED wire to a SPARK PLUG. (Finer secondary coil wire means more room for more turns and more voltage, but its higher resistance means less current - it's a trade off. We are looking for STEP-UP transformer action here and therefore few primary turns to many secondary turns.) The spark plug circuit's return path is through the engine casting back to the other side of the secondary coil winding.
Most of these old coils can be brought back to life simply by cleaning the connections under the terminal bolts. Corrosion makes a great insulator!
The insulator inside the base of the spark plug must be kept clean because the electricity from the magneto can leak through the carbon on the insulator instead of jumping across the tang, making it hard or impossible to start the engine or making it fire irregularly. Even air in the combustion chamber sets up a resistance for the coil to overcome and jump a spark at the spark plug so the gap or heat range is very important. Too much resistance in any given area and it overloads the coil with too much voltage and melts the varnish like insulator coating on the internal wiring wraps and may short out…
A spark plug will sometimes show a spark when tested outside of the cylinder and yet fail to fire the engine when replaced in the cylinder. This shows that the plug is "leaky", because of carbon or because the porcelain insulator is cracked. A "leaky" plug will spark outside the cylinder and not inside because the spark can jump through the air easier than it can jump through the compressed charge inside the cylinder, especially when the engine is cold. Trouble is sometimes caused (especially in two cycle engines) by spark plugs that do not extend far enough into the cylinder and thus a pocket is left at the end of the plug in which dead (burnt) gas collects. Such gas can not be fired by any spark. Spark plugs so located tend to carbonize quickly because they operate at too low a temperature. If your spark plug has been exposed to a gasoline flooded motor “Heave it” it’s now a junk plug…
A condenser is (supposedly) infinitely resistant to DC. BUT, when a DC is dumped into a condenser by the opening or closing of the points, it roars into the condenser, stops, backs up, roars in again, stops, backs up, etc, like waves on a beach on an incoming tide. A condenser cushions the flow of electrons in a circuit like a spring/shock combo. Therefore, when a point makes or breaks, the coil is subjected to what seems to be AC instead of DC. The lowly condenser acts like an oscillator circuit and this combined with the step up action of the coil is what jumps up the volts and fires the plug. It is the SUDDEN collapse that causes the current in the secondary. The main purpose of the condenser is to prevent arching at the point contacts and burning up the surfaces of the contacts which will cause a slow, or un-smooth collapse, thus lowering the strength of the field collapse, and cause either a low, or no voltage to be induced.
Too big or small of a condenser doesn't do the job because condensers store energy . An ignition circuit needs a condenser that is matched to the coil, and the voltage source, and the RPM of the motor. Too much capacity acts like none at all, and too small of capacity acts like none at all. Condenser design - ignition design somehow takes into account the natural frequency of the condenser.
Usually if you see a yellow spark at the plug it means the condenser is going bad. If you are cranking over an engine without the spark plug connected, never disconnect the wire from the mag nor let the spark plug wire hang. Always ground the plug wire to the engine block. To do otherwise can cause excessive voltage in the secondary winding, and a breakdown of the insulation on the wires.
The reason for arching - the collapse in the field also induces current opposite to the original in the primary winding. It is this current that causes the arching.
A condenser is able to absorb this excess, and higher electron flow, and store it until the circuit is made again, where it is released harmlessly. Without the condenser, the current would literally "bounce" back and forth in the primary winding, prohibiting a clean collapse of the magnetic field.
I believe that condensers can go bad for at least 2 reasons. One is that they are able to absorb the electron flow quickly but discharge it slowly. The other is that they absorb the electron flow slowly but discharge it quickly. I have had condensers that can not discharge the electrons quickly. They are very frustrating because they will give you a good spark most of the time because they are either over capacitated or under capacitated.
This is a important reason about grounding a magneto. If you rebuild and repaint the engine, make sure the mounting bolts and contact area between the magneto and the engine casting are clean bare metal. Of course that goes for all other contacts and connections in the circuit as well.
This is why I stress everything must be clean - super rusty laminations should be cleaned with naval jell and mounting surfaces of the condenser must be clean and even under the points must be clean for maximum ground to ensure maximum magnetic fields to be set up for the coil to act upon. Even areas on the stator plate where it mounts must be clean. All nuts and screws must be tight and no frayed wires and no cracks in the coil wire because electricity will follow the path of least resistance effecting maximum fire power. Absolutely no oil or grease near the coil or the ignition points area or even on the wires.
I too was ashamed of myself the other day – I changed a new set of points and condenser in my H35 simple right ??? uhh no fire from the coil so I put a new one in - uhh no fire from the coil… I took out the points and set them on the table and hooked up a ohm meter and no continuity at the points and sanded them down steel polishing wool and wow it passed current. Uhh threw 20 bucks over my shoulders buying a new coil for nothing… shot carb cleaner on the points blew that out and had a nice blue spark just like the other coil did. But at least I have a spare coil now… Goes to show you even a set of new Tecumseh points sealed in a plastic bag had oxidized to the point of not passing current ..
Needless to say those points had me walking around like a man lost in a forest trying to figure out what I did wrong changing points and condenser when I’v e done it hundreds of times but I’m not here to scare the hell out of everyone with rocket science because sometimes I get confused as the next guy at times. Sometimes the answer is right in front of your face but you can’t see the forest because of the trees…
Threw a Rod… :thumbsup:
