On my '85 LT250R I'm having a problem keeping the chain tight. I loosen the allens in the very back of the swingarm then I turn the axle till the chain is tight, and then i retighten the allens. But then after i ride for like an hour or less the chain is really loose again. Has anyone else had this problem or know how to fix it? I can see a hole in the bottom of the swingarm where the axle goes through, is there a set screw in there cause I can't see or feel anything in there.