As it turns out the brakediscs on a BMW (which are non-floating discs) sometimes warp.
When mine were warped I decided to renew them with fully floating discs. The movement which a fully floating disc can make allows the disc to loose its heat more easily without warping.
To change this disc you first have to put the Scarver on a center- or servicestand. Like this one or some other.
Then remove the brakecaliper (see the brake-pad-change page) and change the brakepads as well (this is a mandatory thing to do when changing to new brakediscs). So change the pads according to the text as written in this WIKI.
If the caliper is removed loosen the axle bolt. When you have done this then you have to lift front wheel by using a hydraulic or manual car jack. Try to support the bike somewhere under the engine so that the bike is stable. Only the carjack is not enough.
My bike is supported by wome wooden boards
Then remove the axle-bolt completely and slide the axle out.
You now have a loose front wheel and you can change the dics. Remove all the bolts that hold the old disc (don't loose them because you need them for the new disc)
old and new disc.
After this you can remove the old disc and replace it with the new one installation of the new disc is the reverse of the removal of the old disc.
Then the newly installed brakedisc :
Then put back the front wheel and slide the axle back in place and tighten it slightly with the axle-bolt.
Lower the bike again an then fasten the bolt with the correct amount of force.
Put back the brake caliper (with its new pads) and tighten all the bolts with enough force. And then you are done.
Beware of the fact that new discs and pads need to take some 300km (200miles ?) to run them in. After this you can use them fully.
enjoy your disc and ride safely.