Re: 35 miles each way for work , possible ?
I disagree. You CAN make these engines a bit better. Replace the crap bearings with nice ones, clean up the casting, etc. It doesn't make them as good as a name-brand engine, but it certainly makes them a lot better. One thing that helps reliability is not riding at WOT all the friggin time. Almost any engine is not going to like going WOT for 40 miles. Warming up your engine before really beating on it helps too. It depends on how you ride, and the care you take to ensure proper operation.
As far as a 70 mile round trip... I would say try to motorize a recumbent or something. Riding 20 miles gets uncomfortable sometimes on my bike. A recumbent with a large seat would make a long trip much more enjoyable.