My cb750 mentor broke a crank with a non lightened rotor. it was on an 836 kitted, cammed ported motor though.
That's right, I've seen several. A kitted motor, run hard by definition, creates a lot of momentum (inertia?) in the rotor, especially hard downshifts with high compression braking will wring the crank right off. But on accel too, I imagine. Hard to know as the bike continues to run fine until the battery runs down, or you hit the elect starter.
It actually feels peppier for a while, with the DIY lightened rotor.
