Testing Spark Coils

Install the trembler point first. Run down the nuts and bend the support at "A" (Fig. 3) until the point end stands 1/4" away from the coil core when the mounting nuts are tight. Install the upper bridge assembly over the bolts and run down the nuts. Before tightening the four mounting nuts, move the trembler (lower point) until the points meet squarely and evenly. Turn down the adjustment nut until there is .030" clearance between the points when the trembler is held down against the coil core. Run on the lock nut and tighten in place.

Return the coil unit to the test box and hook up the wires as in Figure 1. The trembler tension is then increased or decreased until a continuous blue spark jumps the 1/4" gap while drawing 1-1/2 amps current. If the ammeter reads more than 1-1/2 amps, decrease the tension by prying up on the trembler support at "A" with a screw driver. If the ammeter reads less than 1-1/2 amps and the spark is weak, bend the support down at "A" by tapping it with a hammer, thus increasing the tension. The adjustment cut "C" should not be moved when setting up the coil amperage as this would alter the .030" clearance required to keep point arcing at a minimum.

We have described the procedure for testing and repairing coils externally. If you are ambitious and do not mind getting a little involved, you may be interested in experimenting with the mysterious works inside that little wooden box. To aid you in following the text please refer to Figs. 1, 2, 3 in the February issue.

If a coil is found to be defective after cleaning and testing as described above, internal repairs are necessary. The windings should be tested first, as it is a waste of time to fool with a coil with shorted or burned out windings. This is where the double-compartmented tester previously mentioned comes into play.

Pick out a coil that is known to be in perfect operating condition and slip it into one side of the tester. Place the coil in question in the other compartment and hook up the wires as shown in Fig. 2. Place a jumper across the points of the questionable coil to short them out of the circuit along with the capacitor inside. Now the windings on the bad coil will operate off the points and capacitor (condenser, if you will) of the good coil. A steady blue spark of equal intensity should arc across both 1/4" gaps simultaneously. If this does not occur the windings are shorted and you should "deep-six" the coil and try another. If a good spark arcs, then either the capacitor is bad or one or both wires have twisted off the bridge mounting bolts inside (G and D of Fig. 3).