My Big Twin was showing intermittent spark when I decided to put it back in service after 40 years in storage. I had been pulling the plugs and squirting fogging air in the cylinders while cranking it with a spark tester attached to the spark plug wires every couple years. The spark always looked good. I thought it was about time to clean and adjust the points.
I was SHOCKED at the total disaster I found under the flywheel. Broken plastic everywhere. The plastic sand had gouged the breaker cam and I could see carbon tracks where the spark had been jumping across the gaps in the insolation.
It was found that the first plastic covered coils melted with heat and age. So starting in the mid ’50s more hardener was added to the mix. My Big twin is testament to what happened then. The coils are built in a "Clean Room". The air is dehumidified and filtered. The coil molds are put in a vacuum chamber and then the liquid plastic is drawn in by the vacuum.
If the coil becomes unsealed, dust and dirt enevenably follow. With the heating and cooling of service these microscopic bits erode the insulting paint on the magnet wire causing microscopic shorts which reduce voltage. The sealing paint you add to the cracks also seals in the dirt already there . . . It is only a matter of time. . . 🙄
