Re: chain rubbing chainstay
If it's already worn a "groove" in your chain stay, I can tell you, from personal experience, now is the time to find another bike to put that motor on. Like Tom said find a way to get the chain away from the stay for now, in the end you'll be much safer on a bike that has room for the motor chain.
"I would rather be exposed to the inconveniences attending too much liberty than to those attending too small a degree of it." - Thomas Jefferson