Lately I've noticed that a lot of the coils on old B&S engines left at the tip at first appear dead, as they give no spark, or show no reading on testing, or very erratic readings, but they are in fact still good working coils. With a bit of effort these can sometimes be repaired. What I have discovered is that a lot of these coils are still perfectly fine. The only thing wrong with them is the lead wire has broken off where it connects to the coil. I am not sure if it is to do with years of engine vibration, operator's repeatedly taking the leads off and on to clean and change plugs, or more likely rough operators who are yanking on the leads. Moisture also seems to seep into the join over time if mowers have been left out in the weather or often used to mow very wet grass.
I only discovered this when one coil that tested perfectly okay was put on another engine but then produced no spark at all. This left me scratching my head for a while. I could not work out what was going on as it was okay one second, not okay the next. So I tested it while moving the lead around and sure enough found it was cutting out on certain angles. Diagnosis is broken or faulty connection between lead wire and coil.
Here is my fix. Note: You will need to hold the coil in something like a vice. You will also need some way to heat up a small amount of lead (I just used a Hot Devil torch), plus a small tin pourer to melt the solder in, pliers to hold the tin when it is hot, a small soldering iron, solder wire, electrical wire cutters, a small screwdriver, and a drill.
1) Cut off the lead wire flush with the coil and using a small drill and a screwdriver carefully work it around the pin until you hollow out the space all around the pin, being careful not to damage the outer plastic of the coil. I did not worry about chopping through the existing connection because it was faulty anyway, but made sure to leave the cut off wires still visible against the coil side of the hollow.
2) Then melt some lead solder in a small container and very carefully tip some of the molten lead into the hole. You only need enough to form a contact between the pin and the coil wire.
3) Next use a soldering iron to melt some more light solder on top of this.
4) Test the original lead wire for connectivity while flexing it around. If it tests okay, cut the lead wire back to expose about 1 cm of wires and spread these wires about in a rough circular manner. The idea is to work the wires around so the lead can be easily fitted back into the hole.
5) Next plunge a very hot soldering iron into the hole and swirl it about until the solder has formed a pool. Do this while holding the lead in your other hand. Work fast before the outer plastic on the coil begins to melt. If some melts don't worry, you can repair that later with hot glue.
6) Quickly plunge the lead into the hole of molten solder and push the centre of the lead well down into the pin. Then hold and blow on the soldered part until it has cooled.
7) Next get a glue gun and completely seal up with a big blob of glue. This will also help support the wire. It may not look pretty, but who will notice? It fits inside the engine.
8) Test again with multimetre. You should now get a good, stable reading.
I have done this to three coils so far and got them working again!
