physical contact between the cap and rotor
 

What would cause the rotor to "groove" the electrodes inside the cap?

How can I avoid this after a rebuild?

I'm sure this is robbing power

Its only 2 or 3 that are grooved.
12A 1984 stock, for now.

My guess would be either the cap (most likely) or the rotor were not in place correctly. Many caps have been knocked out of place by broken fan belts.

There's a thread around here that shows a rotor that was totally beaten to a pulp from contacting the inside of the cap. Twisted like a corkscrew. Car amazingly was still operating.

They are prone to getting misaligned from being bumped or mis-seated, apparently.

Never had the issue myself.

My car was running terrible for a few months. Couldn't figure it out. Tried everything. Finally I replaced the cap and rotor and it did the charm. Found out that my cap was just chewed to shit. The car had zero power under load.

in extreme circumstances it could also be caused by the shaft inside the distributor body actually being bent, im not sure how common it is on rotaries, but ive seen it happen to several V8's

do you have the metal dust cap that goes under the cap? if not, maybe the cap is sitting slightly too low?

I had the same problem, but I think the po just put it on a little crooked. replace it and make sure its on there good. If it happens again and your sure its on strait somthings wrong. But since it only damaged 2 or 3 most likely it was misallighned. if its miss aligned some of the conectors not getting chiped may also not be getting a good spark that may be whats robbing your power and some mech risistants due to grinding but the chiped ones are getting power more than likely since its actually touching the rotor

if it was the dist itself most likely all parts would be toast.

I had this happen once. It turned out the bearing/bushing was worn out and caused a slight wobble which kept chewing up cap and rotors. I ended up just replacing the whole distributor but I guess you can get a rebuild kit.

Thanks guys I'm gonna give the stuff a try. I think the bearing is the most probable. I shoulda figured that out, been dealing with ECU's for so long I got lazy and forgot the basics. Thanks again