Possible Leak in Starter Circuit?

[Colonel Biggs]

I have been having an intermittent problem with a starter. One of the insulated brushes has lost some of its covering. I don't know whether this could cause an arcing when the starter button is activated. Sometimes I can get the starter to spin nicely on the bench; other times, just a spark at the terminal post. I have checked the field coil circuit, and there is no shorting there.

In running a continuity test on the two insulated brush holders to the end plate, one of them shows a reading of “9.5” on the 10K scale, and the other brush shows about "100" ohms on this same scale. I believe this amounts to 95,000 ohms in the first case, and one million ohms in the second? What I don’t know is the significance level of resistance readings of this magnitude. Since there is not supposed to be any continuity between the end plate and the insulated brush holders, I suppose that I should opt to replace the insulators for these four rivets before putting the starter back on the car.

If anyone has any thoughts on the electrical math involved here, I'd like your thoughts.

Gordon