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SUMMARY: Personal Experiences


I have had over 35 years of electronics experience, but I only learned recently about magnet KEEPERS. Unfortunately some things have to be learned the hard way. If you take a magnet out of a magneto, it will be weakened to the point of near uselessness and the only way to recover the magnetism is to use a magnet charger. Additionally, NEVER take an "armature" out of a magneto either, without anticipating the usage of a magnet charger or a keeper.

 (front of magnet charger)  (rear of magnet charger)

(Front & rear view)

This magnet charger was made by Joseph Weidenhoff Incorporated of Chicago, IL and uses Tungar Bulb rectifiers with a 120 volt power source. The soft iron blocks in the foreground are used to direct conduction of the magnetic field into the magneto's internal magnets. The 25 watt light bulb in the center serves to absorb back e.m.f. Charging a magneto is accomplished by giving it three or four magnetic jolts of 5 seconds each - your procedure may vary.

Tungar Bulbs predated the selenium rectifier and of course our most recent silicon rectifier. They were also used in the automotive and radio battery chargers of that era.

(Tungar Bulb)

The rectifiers are used to change the incoming 120 volts AC to direct current so as to cause the current to flow in ONE direction through the coils. This sets up a directional MAGNETIC flow through the magnet placed on top of the coils with the magnetic circuit being completed through the cast iron base. Tapping on the magnet to be charged with a small hammer while the charger in energized, causes the molecules within the magnet to align themselves with the flow. The north pole of the magnet is placed upon the south pole of the charger and vise versa. Once the magnet is charged, you have to place a bar inside it as a KEEPER or charge the magnet right inside the magneto.

Here's a Wico sitting upside down on top of the charger poles, waiting for a few jolts. Make sure you get the polarity right! Note that the internals are showing the front side and the one on the charger is showing its backside. Using a compass, mark your charger North and South and then the magneto North and South. North on the mag sits on South on the charger, which completes the magnetic circuit in a loop. The armature will jump up during the charge and then settle back down. In this case, the armature serves as the keeper by completing the magnetic circuit through the wico frame. For what it's worth, I don't remove the armature from a Wico without concern for recharging it. According to Wico factory literature, it doesn't matter, but every little bit helps by way of holding the charge. The base of the Wico is made of non-magnetic pot metal.

Charging a Wico Magneto


Over the years, I have learned generally to blame a power supply for problems first and measure its voltages for proper values. This can save hours of troubleshooting time by getting right to the source of most electrical difficulties - heat. Capacitors for example are made up of paper, foil and chemicals. Heat and time will dry out these chemicals and as this happens, the capacity value diminishes to a point near NO capacity. Capacitors are used in magnetos and coil systems to help increase the amount of spark output. As the capacitor's value diminishes, so does the spark intensity.

The cap in the foreground is the original rubber covered ol' timer from the Witte's Wico. Measuring its resistance showed that it must have had extreme leakage current. This leakage causes a coil not to discharge as rapidly as necessary to cause a hot spark. The cap in the background is the "newer" type. Either will fit inside the cavity at the top of the Wico. Notice that one end of the capacitor is grounded and the other end connects to the points. The point end MUST be insulated and kept from making contact with the frame!

At left is the dismantled Witte Wico. (see Witte story) Notice the nubs at the top of the fame - this is why you can place the Wico upside down on the magnet charger for charging its magnets.

After rebuilding a Ford 2N to the point that nothing should go wrong, one day while mowing the field the tractor lost power. It would start and sort of run, but its get up and go had gone and went. I was suspecting everything that I had done, like valve tappet clearance, carburetor, fuel line, coil, etc. It turned out to be the capacitor across the points in the distributor and it was a brand new one! It was obviously cheaply made, so newer is not necessarily better. I put the old capacitor back in and everything was back to working again!

Another source of difficulty is the short circuit. These can happen anywhere, inside components or outside in the main pathways. A capacitor can short out due to a direct pathway between the foil layers that are separated only by a layer of chemically wetted paper. It can also become leaky - not an absolute short, but close to it. Coil windings can contact one another and steal energy. Imagine if you can, adding a small coil to a transformer, but shorting its output terminals. All of the energy consumed by this winding is dissipated in the form of heat as it has nowhere else to go. If one or more turns of your spark coil are shorted, the same situation is true. The only way to find this out is by measuring the resistance or inductance of the coil and comparing that to a known good one. Of course spark plugs can become carboned up to the point of conducting the electricity through the carbon rather than through the air gap that ignites the fuel. Damp insulation on the spark plug wire can leak off energy at any point where it comes near the frame.

Spark Plug

An open circuit can cause difficulty too. Not completely open - that's OFF, but just a little open as in a loose connection. A pair of coils such as in a Wico magneto, must have an interconnection between them. If this loose or open connection is on the high tension coil windings, the voltage arc will probably jump the open gap and still have enough voltage left to make it on out to the spark plug. It will be weaker than it should be though. If something is loose in the low tension windings then there is not sufficient voltage to jump the open gap and nothing will work.

In operating an old engine, don't make the mistake of setting the spark plug gap too wide. These magnetos are not able to overcome wide gaps under compression. What may look OK outside in a plug arc is a different story when soaked with fuel, carboned up and under compression. .015 or .025 is about right and the old .035 automotive standard is too wide. The insulator inside the base of the spark plug must be kept clean (free of carbon), because the electricity from the magneto leaks through the carbon on the insulator instead of jumping across the points, and makes it hard or impossible to start the engine. A plug will sometimes show a spark when tested outside 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.

Clouds of BLACK smoke from the exhaust indicate too rich a fuel mixture. Screw the needle valve in a bit until the smoke disappears. If the engine misses or fires back through the carburetor or mixer, the mixture is too lean. Gray smoke indicates that the oiler is providing excessive oil or that the rings are allowing oil into the area above the piston. NEXT PAGE: >

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