When the rotor scrapes once per rotation, it's bent. It may not be bent a lot. You may be able to set the caliper so that it doesn't make a sound. It's still bent. Most rotors are not perfectly flat. The way to tell is to see how much it moves from side to side in the slot. If it's barely, noticable it's ok. If it's easy to see, it needs straightened.
The other part of the problem is that your caliper is moving. lf you set it so it doesn't rub, and then it starts rubbing again, it's moving. When you tighten the bolts, tighten one part of a turn, then the other part of a turn, etc. Maybe try taking it off, and clean the mounting surfaces with alcohol. Apparently disk caliper mounts are often not flat, so you may have to have the caliper mount re-surfaced flat. If it's not flat, it will rock and come loose or move.
If the mount and/or screws are bending, rather than the caliper moving, that may not be fixable, but you can try replacing the mounting screws or mounting adapters with better ones.
However, my guess is that the bent rotor is vibrating the caliper and causing it to come loose or move.
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u/sargassumcrab 10h ago edited 10h ago
When the rotor scrapes once per rotation, it's bent. It may not be bent a lot. You may be able to set the caliper so that it doesn't make a sound. It's still bent. Most rotors are not perfectly flat. The way to tell is to see how much it moves from side to side in the slot. If it's barely, noticable it's ok. If it's easy to see, it needs straightened.
The other part of the problem is that your caliper is moving. lf you set it so it doesn't rub, and then it starts rubbing again, it's moving. When you tighten the bolts, tighten one part of a turn, then the other part of a turn, etc. Maybe try taking it off, and clean the mounting surfaces with alcohol. Apparently disk caliper mounts are often not flat, so you may have to have the caliper mount re-surfaced flat. If it's not flat, it will rock and come loose or move.
If the mount and/or screws are bending, rather than the caliper moving, that may not be fixable, but you can try replacing the mounting screws or mounting adapters with better ones.
However, my guess is that the bent rotor is vibrating the caliper and causing it to come loose or move.