http://www.bikeengines.com/

This link is to what my research tells me is the best alternative bike engine. You can get a 4 stroke option so no oil/gas BS. At first I was skeptical about applying load to spokes, as this system does, but after looking at it with my engineering rational, I see it's the best way to distribute the load over 32 or 36 points.

There are a huge number of examples of sucessful installations with related stories. They even ran a test at Bonneville Salt Flats; there's a You-Tube video on this. Just Google "Golden Eagle Bike Engine" without the quotation marks of course.

They claim to get up to 200 MPG with this setup, no wear on the bike's tire (since there is no friction roller on the tire), and no mechanical drag if you want to disengage the motor drive. It looks to me to be the only power assisted option for touring that makes sense except I have considered installing one of these engines on a trailer so I could just park the trailer and have a completely stock bike while at camp.