Hi. I have a 1984 Honda xr 500 dirt bike. The sprocket is well worn and it has a fastener with two bolt that hold it up against the sprocket. I'm ordering a new sprocket and fastener and wanted to know how the sprocket will keep from moving in and out on the spindle shaft? It won't have forward and reverse play but what keeps the sprocket from sliding in and out? The old one seems to have some play in and out of the shaft. About a half inch. Is there something else missing? A spacer of some kind? Thanks for any help......