I have a road bike I use for commuting and I'm about to move 20km further out, so I'm considering fitting a tiny engine to it to assist my ride to work.

However, where I live I have a restriction - the maximum power allowed is 200 watts (about 1/4 HP).

I've seen [some kits][1], but they have huge engines (beats me why they have to be so big).

Further, I'd prefer a diesel engine (no spark/glow plugs) and better economy.

Some brief research has shown that a tiny (1cc or so) diesel engine should be able to produce about 200 watts. A larger one could be de-tuned. There are model aircraft diesel engines of this size, but they're quite expensive.

I've been told a "brushcutter motor" (small two-stroke) could be an option, but they are noisy, smoky and smelly.

I'm not worried about how to deliver the power to the wheel - I'm trying to pick the power plant first then make it work.

Has anyone got any suggestions for:

- diesel engine
- very small (200 watts max)
- not expensive

  [1]: http://zbox.com.au/zbox-picture-gallery.htm