Distributor Question

[connecticut mike]

While troubleshooting why my '30 Coupe suddenly stopped running when idling, I noticed a dark black spot in the distributor rotor where it contacts the carbon button in the cap. I suspected arcing, but the spot polished off using Scotchbrite and there were no signs of arcing. The carbon button in the cap seemed shorter than I would have expected - about 1 mm beyond the raised bakelite area surrounding it.

A few questions, please:
- Does this button wear, like brushes in a motor?
- Is the black spot a normal condition?
- How much should the carbon button extend beyond the area immediately
surrounding it?

Thanks, Mike

[johnbuckley]

Does this button wear, like brushes in a motor?
Yes this button wears down. Sometimes people never check them and the rotor arm spring starts wearing down the brass surround of the button
- Is the black spot a normal condition?
Never seen a black spot , but often see a shiny spot where button seats onto the rotor arm spring. Like you, if black spot present I suspect possible arcing.
- How much should the carbon button extend beyond the area immediately
surrounding it?
About 2 mm ( 1/12 of an inch in your fractional terms!) here's a picture of a brand new unused one

[Big hammer]

As usual John is spot on, when you reinstall the cap make sure the rotor pushes back on the cap, the rotor spring can be bent up so to make a positive connection

[connecticut mike]

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John and Big hammer,

Thank you much for your prompt responses.

Mike