trac olympic 86 moped. A new drive chain I received does not fit exactly over the rear sprocket (leaves gaps when you try to tighten it--. A little extra weight or bounce makes it jump off the sprocket and stop the bike and me with it of course. bike has only 2-3000 miles. I can't find the old chain so I'm not sure if it is the wrong size or maybe I have a worn sprocket. Do I buy another chain(past dealer no longer avail)? Sprocket? How do you measure the chain that you need if the one you have is the wrong one? Can you just replace front, rear sprockets, and chain? What size? I'm totally confused but determined. sprocket has 44 teeth, and links on chain measure 8 mm between small bolts on one link. front sprocket has 12 teeth. HELP?