The RFS engines have multi-piece press fit cranks. When used consistently at high RPM, the cranks will twist at the joints. This is especially a problem with the long stroke engines - 450exc's, all 525/30's, & 560 SMR's. The 450 exc uses the same crank as the 525's. The joints are welded and ground down. Its a good idea to have it performed on any motarded RFS engine.
Try these guys. They are one of the best motorcycle crank shops around.
www.faliconcranks.com