I'm running a 7 speed rig. The derailleur is the right one for the speeds. I'm using an old Suntour Cyclone. I'm using a SRAM PC-830 chain. The derailleur doesn't rub on the ends (where slightly bent inwards to prevent overshifting), but rather in the centre of the cage. This happened with the stock Huret derailleur too. As for a weak frame, probably not. I tried the two piece crankset a couple weeks ago and there was absolutely no rub. I could align the derailleur and just barely put in a penny with no rub. I'm pretty confident that the chainrings are true.