Rotor Hitting Cap
 

I have an 82 RX7 motor, the car had a misfire so I was checking things. I noticed the rotor was getting eaten up on top and the cap a rub marks by the contacts. I changed the cap and rotor today and I can see similar marks starting. Has anyone had this happen before?

Mine did that and found the cap was not seating right. I cleaned the lip all the way around the dizzy and reinstalled carefully. No issues since. Is this a new car to you? I would also check for play in the shaft and or rotor.

both the car, and rotaries are new to me. Ive had it since June and got it on the road around November. I know with some distributors you need to shim between the gear and body to help eliminate play up and down, and it does steady the distributor shaft a little at high rpm. Is it possible I need to do that. Whats odd is only 2 of the tangs on the rotor at the top rubbed. The other 2 didnt. Also it rubbed just the plastic and the edge of the contact going around. Tried to take pictures but its hard to see. Now would side to side play actually cause that? I did make sure the housing was clean and the little metal cap under the rotor was seated. Does it actually have a position it locks in? I turned the metal cap until it kind of dropped in and locked into the housing. Then i pushed the rotor on as far as it would go. Then I lined the Distributor cap up and locked it down. Kinda standard stuff. The only thing that seems odd to me is wear up top as opposed to the sides of the cap.

this happens if you mix up brands of cap and button i.e echlin and bosch

one way you need to put some cardboard under the button and lift it up to suit
but vichy versa will just chew up the cap

Almost always a sign that the cap was not seated properly & was canted a bit.

If it was the shaft running off-center, you'd be beating up the pickup coils too as they only have a few thousandths clearance from the reluctor wheel.

I've always replaced cap and rotor at the same time,with same-brand parts, and never had an issue with fitment. I did get the cap on crooked once, though. Made an ugly noise on start up.