We recently bought a 2003 Co-Motion Speedster to which we are trying to adapt a child stoker kit from our previous tandem. (Should have kept it just to ride with the youngest one, but don't need 3 in the garage) The bike has Ultegra cranks with 38T chainrings at 130mm BCD. There is just enough room to mount the inner 38T chainring that is driven by the stoker kit (or that drives the stoker ) but when the chain is attached it (the chain) rubs on the chainstay, just barely, but enough to scratch the paint. My fear is that this could eventually damage the frame slightly, or at a minimum, provide a place for rust to start.
Any suggestions on how to overcome this would be appreciated.