Player nao trava a rotação no x

to quebrando a cabeça aqui mas nao sei o que pode ser, meu player nao trava a rotação no x, se coloco o mouse muito perto do player, o player na unity meio que fica deitado...

m_rigidbodyPlayer.MovePosition ( m_rigidbodyPlayer.position + ( dir * Time.deltaTime * m_speed ) );

        Ray ray = Camera.main.ScreenPointToRay ( Input.mousePosition );
        Debug.DrawRay ( ray.origin, ray.direction * 50, Color.red );
        RaycastHit hit;

        if ( Physics.Raycast ( ray, out hit, 100, m_floorMask ) )
        {
            Vector3 aimPlayer = hit.point - transform.position;
            aimPlayer.y = transform.position.y;

            Quaternion newRotation = Quaternion.LookRotation ( new Vector3 ( aimPlayer.x, transform.rotation.y, aimPlayer.z ) );

            m_rigidbodyPlayer.MoveRotation ( newRotation );
        }