H-D 6 volt coils

[cubman]

When a coil goes bad what is it that goes wrong? Does a wire burn thru and can the coils be repaired? Trying to learn a little more, thanks, Mike

[Robert Luland]

If your lucky, they miss fire long enough to get you home. One of the other treats is to stop firing and all a sudden it come back to life after you kicked your ass off and it cooled down, only to do it again 30 minutes later. Bob L

[Rubone]

Generally it is an internal short due to overheating and damaging the insulation in the wiring, which is just shellac or in later coils an epoxy type material. That changes the resistance and creates the issues. Coils work by creating a magnetic field with one set of windings outside of another which creates the voltage change needed to fire the plugs. When the windings break down the coil fails to produce the needed energy. It is basically a step-up transformer creating extremely high voltage with very little amperage. Your home operates on a step down transformer going the other direction. A bit of Black Magic as there is no physical connection between the windings. Lots of stuff works in similar ways. Such as brushless cordless tools, they are all induction driven.

[cubman]

Thank you for the help.

[Chris Haynes]

Harbor Vintage had a coil restoration service. I don't know if they are still doing it or not.

[cubman]

Thanks Chris, they did rebuild the coil for my ‘34 B.

[Steve Slocombe]

An old tip from Harley is to deal with the mastic inside the coil slumping down to cover the contacts. Find a piece of copper tubing the same diameter as the plug wires, cut saw teeth in one end, and use it to core out the offending mastic.

[RichO]

Steve, What's always worked for me is to heat of the coil to soften the goo and the wire slide right on down to the spike in the bottom which impales the core wire and when it cools down, bingo.

[len dowe]

Isn't it tar? I always thought it was and with Steve's recommendation to core the coil and then clean the contacts.