A person standing on a stationary friction-less turntable spins a bicycle wheel with the rotation axis of the wheel in the horizontal direction, thus the initial angular momentum is in the horizontal direction (x - axis), say to the right. Now suddenly the person turns the axis of rotation of the wheel by 90 degrees upward (final angular momentum of the wheel is now directed upward along the y- axis). I understand that the initial angular momentum along the y- axis is zero. Thus we expect the final angular momentum of the system along the y- axis to be zero as well. So the person + platform will spin finally in the opposite direction of the spinning wheel. But the problem I am having is with the initial x - component of angular momentum. How do we account for a final x- component of angular momentum? If there is no final angular momentum in the x- direction, then this means that angular momentum is not conserved! contradiction! Any help would be appreciated. Thanks.