Building a WICO EK Magneto Tester

Rob Skinner's mag tester

Rob Skinner's WICO EK magneto tester. The fulcrum bolts also act as a stop so the armature can't be pulled off. 

Photo by Rob Skinner

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Much of the challenge of restoring old iron is devising methods of repair utilizing the tools available in the workshop. Sometimes we have the proper tool for the job, sometimes we can improvise, and sometimes we have to make our own tools.

When my friend Gus Lukrofka dropped off a crate full of old WICO EK magnetos, I was faced with the problem of having inadequate testing tools. Certainly, each magneto could have been tested by installing it onto an engine, holding the spark plug against a metal surface with one hand and then turning over the flywheels with the other hand. However, testing a large number of magnetos that way didn't seem very appealing. But a little digging through the scrap metal pile and an evening putting the parts together left me with the magneto tester pictured here.

When testing an EK, the primary goal is to pull the armature from the core in a quick, snapping action, which will generate a spark if the magneto is in working order. If the armature is pulled away slowly, the magneto will not spark. Further complicating testing is the fact that when the magnets are properly charged it's very difficult to pull the armature by hand, which means a lever of some sort must be used.

In order to maintain simplicity in the design, a fixed lever was not used. The lever is a 1/2-inch combination wrench, which also doubles as the wrench used to tighten the 5/16-inch bolts that attach the magneto to the tester.

The fulcrums for the lever are two 1/2-inch bolts that are placed in a position that will allow the wrench to push the armature up, as well as pull it down. Another consideration for the placement of the bolts is that they should be directly below the armature. There is nothing on an EK that prevents the armature from being pulled completely off, so the top fulcrum bolt also acts as a stop for the lever.

Above the magneto is the spark plug mount. It is a 1/2-inch pipe coupling that was cut off so the electrode of the spark plug is visible. The spark plug screws in from the back side, and the grounded electrode on the spark plug should be cut off. Why? Because on a good magneto, the spark will jump the 1/4-inch between the center electrode and the body of the plug. If the spark will only jump .030-inch under atmospheric conditions, it will not fire properly under compression, so testing with a properly gapped plug doesn't prove much.

A warning when testing ANY high-tension magneto: Always ensure that the spark plug wire is either grounded or connected to a properly grounded plug. When the magneto is installed in a running engine, the spark will jump the gap between the electrodes at about 8,000 volts. However, if the spark plug wire is disconnected, the electricity in the coils can build up to 20-30,000 volts. This electricity will seek the easiest path to complete the circuit to ground, which can be through the insulation of the coils. This 'shorting' will cause degradation of the insulation and possible failure.