Testing Spark Coils
(Page 3 of 4)
Remove the sliding panel side, of the coil box by withdrawing the two little nails at the bottom (E, Fig. 3) and sliding the panel downward and off. Now you are confronted with a great lump of black tar! Study Figure 3 and proceed to carefully dig out the tar little by little with a screw-driver from the area under the four point mounting bolts. You may strike the top of the glass partition (H, Fig. 3) or little wooden spacer blocks. You can dig these loose and pry them out if they are in the way. If you are lucky, the wires will be soldered to the two bolt heads closest to you. If not, you will have to dig deeper to expose the lower bolt heads. If one or both of the wires are broken loose, solder them back to the proper bolts and retest the coil as in Fig. 1. It is not necessary to replace the panel to make the test.
If the coil is still found to be weak the final repair to make is replacement of the capacitor. Dig out all of the tar from over and around the old capacitor and pry it out with a screwdriver. Cut off the wires connected to the top and bottom of the capacitor, leaving tails as long as possible. Remove the glass partition and any loose wood spacers. Do not disturb the tar surrounding the core windings.
The best capacitor to use is a 0.5mf in the 400-800 volt range. These can be purchased at any radio or electronic store. They come in various sizes and makes so it will be necessary to pick one that will fit best. None, however, are anywhere near as big as the old ones. A Mallory or a Cornell fits well if you remove the glass portion. These are about 3/4" diameter by 2" long.
Solder the two leads on the capacitor to the two wires that were connected to the old capacitor and position the new capacitor as far away from the core coils as possible. Make sure that all the leads are well clear of the core coils. If you do not, they will short through the insulation and the tar which is poured around the core windings.
After everything is in position, pack the voids and spaces with wads of paper, cardboard, or small pieces of wood. It is a good idea to replace as much of the glass partition as room will allow. Now retest and adjust the coil as previously described. With the new capacitor, the coil should work better than it did when it was new, providing the repairs have been properly made.