I haven't taken the bike part yet but here's my problem. I have a Hasheng 4G transmission and what has happened is the sprocket that drives the chain doesn't seem to be connected any more. It won't drive the chain. The nut is tight but it seems the sprocket has some how become disconnected to the shaft? Without taking it apart I'm not sure how the shaft connects to the sprocket? Is there some sort of bearing in there?