Hi there I have been working on my SR for a while now, its now finally getting to the MOT stage. the previous owner put a larger back wheel on, I have the original wheel which I wanted to put back on the bike as the larger wheel looks silly.

But while unbolting the back sprocket one of the 4 bolts holding it in place sheered off!, this is probally a daft question but im new and in experienced with these matters but I was wondering if those 4 bolts are changable? the ones that hold the sprocket.

Pretty much everything is replaceable. Get a manual, find the part number, order a replacement.