I have a 91 Honda Civic. It has almost 166k runs fine except for some upper engine noise when cold.

The rotor keeps coming off & no one can figure out why. We've replaced the cap & rotor at least 5 times & the distributor once. We thought maybe the cam was moving too much & that was causing it but it wasn't. It does it randomly driving fast, slow, or even parked. Usually it sheers the head of the bolt off & the rest of the screw is stuck in the shaft & has to be drilled out.
We are all stumped, if anyone has any other suggestions feel free to run them by me. This has happened 6 times in the last 4 months & I'm really at my limit with this car.

Try a matched BWD distributor cap and rotor, which come with a lifetime warranty. Is there evidence of the rotor hiting the contacts inside the distributor cap? Is the bolt OEM?

I have had Firestone put in the first cap & rotor. The other times it has been my ASE certified mechanic putting parts purchased at AutoZone. The cap doesn't appear to have any damage that's why we are all stumped. The bolt was OEM after we fixed the distributor but then it broke off again anyway & we had to drill out the old one. The last time we even used a hardened bolt (grade 8 possibly but not sure) & it still sheered off but this time it didn't stay in the shaft. Seems like regardless of new parts just continues to happen.

That's a first. Never heard of anything like that over the years.

That's the response I keep getting... No one has a clue so I figured I'd branch out. Any ideas would be helpful...

I would install a new genuine Honda distributor housing with an aftermarket igniter and coil to keep the cost down. Most Honda distributors only last 50,000 to 100,00 miles anyhow. Then, you would have greater reliability and save on labor costs.

We have replaced the distributor & that obviously didn't fix the problem. The rotor did this 4 times before we fixed the distributor & 2 times since then. I give up... no one knows why, just bad luck I guess...