Coil potting compound?

[T. Cotten]

Un-answered question #239:

What was the potting compound used inside of vintage H-D coils?

Many thanks in advance for an accurate answer, because it sure ain't "tar".

....Cotten

[WebKahuna]

I don't know the correct answer, but I believe that Gutta Percha or Wax was sometimes used for early electrical potting compounds

[sswaney]

Cotten!

I used refined bitumen for the coils on my J model. It was the only thing I could find that appeared to match the original material and mixed well with it when heated to a pourable liquid. I sourced it from a local hot roofing contractor. Actually they let me pick up a couple of chunks from their storage area. It comes in a large paper wrapped cylinder that weighs about 100 lbs. Once it cooled it was indistinguishable from the original stuff.

[T. Cotten]

Mister_Blank!

That sounds appropriate, but I wonder if it resists mineral spirits, and even canned carb cleaner, like the original?

The modern 'tar' on my roof dissolves easily, and it came in rolls like you mentioned.

The reason I asked is because similar stuff was apparently swabbed inside of my '65 fuel tanks, and I still wonder what the similar stuff was that was used to glue in Panhead felts.

.... Cotten

[sswaney]

Tom,
It does not resist mineral spirits. I did a test on my coffee can used for liquifying the stuff and mineral spirits cut it with ease.
It has held up in the J coils though with no discharge when warmed to operation temps.

[T. Cotten]

Well Folks,

Mineral spirits will dissolve the coil compound slowly, or quicker with heat.
Xylol cuts it much better than spray carb cleaner, so it may well be a "bitumenous" compound.

Not only would I like to know more about it, I earnestly would like to know what the tank swabbing might be, as it resists all solvents, even P4gas.
And the Pan felt adhesive is a mystery all of its own, as it not only resists oil, it resists the heat of a motor.

We may never reclaim this knowledge that was commonplace but a half-century ago.

....Cotten

[awander]

It's crazy, isn't it?

We should keep in mind today, that what we think of as common knowledge, may also fall by the wayside....

[cdndewey]

No it won't resist mineral spirits at all. When I used to roof we used baby oil to dissolve/remove any...we called it tar...from our skin if we got any splashed on.....which happened more than once in my carreer as a roofer.

If you can get a hold of a product by Tremco it's quite resistant to mineral spirits. It comes in kegs like tar, but smaller and it's a little more rubbery than tar. It's heated in a kettle like tar and when heated to about 400 - 500 F it will flow. It may flow a little/enough at a lower temp, but as a roofer the hotter the better to mop with, so I only dealt with 500 F plus.