Dahon Classic III crank arm bolt won't stay locked
I recently picked up a Dahon Classic III and today was the first day I've used it for my commute. During my 4 mile ride to work I had to stop four or five times to re-tighten the bolt that secures the folding crank arm in place. When I get home, I'm going to tighten it down with a wrench, but I'm not sure that's a good long-term solution (and I don't want to tear up the threads by spinning it down too tight). Has anyone else had this problem? Does anyone have a decent fix they can recommend? Or is this just the price of the charm of riding a weird, old bike?