Compensater Sprocket

good idea I'll try to find a tab washer big enough .no way to double nut

You may have to tack weld the washer to the face of the cover so it can turn, or drill a hole in the cover so you can been a tab down into the hole so the washer can't turn and and allow the nut and washer to loosen up. In any case if ya can't find one big enough you can always make one out of a big washer. I would make sure to have a couple of tabs on it to bend against the flats on the nut. Never know where the flats on the nut will end up when you torque it to spec.