i am using a toro self propelled lawn mower. it starts fine and continues running, but when i raise the drive bar/engage blades bar, the blades won't engage. the self propelling mechanism works fine. i can manually turn the blades, however, it seems "tight" and seems as if something is rubbing (i can hear a metal scaping sound). does anyone know if this is something that i can fix myself, or is this an expensive professional job?