I have a set of Galfer wave rotors that survived a hit and run accident on a 919 last spring. To the naked eye they're in perfect condition, but I just put them on my new 919 and one of them scrapes slightly with each rotation, so it's a little bit bent. The stock rotors went right back on there.
Is there a way to have this rotor straightened or is it scrap? It is noticable when you rotate the wheel, but it seems like a waste to pitch them if it can be fixed, especially since the bend is so slight I can't see it.
Most brake rotors have a small amount of runout that will make the noise you describe to one extent or another without causing a problem.
A bend of as little as 0.005" will cause the noise you describe, but not be visible. Did the front brake pulsate when applied? If so, they are pretty much done for.
The problem with straightening a bent rotor is when it was bent in the first place the metal on one surface stretches slightly and the other surface shrinks, realigning the granular structure of the metal. Straightening will undo this slightly, but invariably creates another set of stretch / shrink lines near the original bend but in the opposite direction. A couple of good heat cycles and the bends reappear.
If they cause a pulsation and you can't find a grinding business that can surface grind them without using a magnetic table I'm afraid they are history.
If it has already been done, it is safe to assume it is possible to do it.
On the other hand, if it has not been done never assume it is impossible to do it.
------- Rob --------
Rob, I didn't even get around to checking for pulsing. One of the rotors was running smoothly when I spun the wheel and the other made a noticable draggind sound at one point every time it went through the pads. I didn't pursue it any further, I just pulled the wheel off and put the stock rotors back on...