this happened to me twice already. i'll drive my car for about 100 miles or so and my rotor will pop off. i tighten the retaining screw that holds the rotor in place to spec. i replaced the cap and rotor about 4 months ago. what could cause the retaining screw to keep coming off? i appreciate the help you guys give me everytime i put up a post.

 

use some lock tight. put a washer on there

 

I would think your talking about the distributer cap rotor and not the ones on your wheels.

 

had exactly the same thing happen on mine (91 Si)

I did use some red lock tight and it eventually stayed on untill i fixed it permenantly..

What i am pretty sure caused it was the distributor bearing being worn out.
Once the bearings wear out the shaft spins off axis and therefore causes the rotor to keep coming off.. also might see some contact between the metal edge of the rotor and the conection points under the distributor cap. I ended up replacing my distributor and seemed to solve the problem..

hope that helps..