Old Dahon/hon rear tire <--> fender clearance issues
A few months ago I bought an old 1980s Hon Convertible stainless folding bike. After fixing the frame latch I was able to ride it. The chain felt a bit loose, so I tried moving the rear wheel back a little to tighten it up. After doing this, the rear tire started rubbing the fender, so I moved it back so it no longer rubs. The chain is still too loose, occasionally I can feel it start coming off before falling back into place.
A few days ago, my son brought home another old Hon stainless folder. It has the same problem. I realize the bikes are 30 years old and all, but it is weird to have the same problem on the 2 that we own.
Are these bikes extra-intolerant of stretched chains? Is this a common problem? Or are the plastic fenders shrinking over time? One bike has orange fenders, the other one black.