I bought the cheapest 4 stroke kit on eBay I could find and put it on a crannbrook huffy cruiser. Problem is that the chain in the gearbox is loose and falls off every 5 minutes. Well this last time it fell off it cbroke a tooth on the small gear. Well since it broke I have looked everywhere for just that gear only so I don't have to replace the whole gearbox and I cannot find one at all or a way to tighten the chain other then trying to take a link out an but a master link but that may not work either. Any ideas or help would be great. Will take a few pictures in a few.