"C J Campbell" wrote in message
news:2007051622171050878-christophercampbell@hotmailcom...

An engine can be made to run backwards. Model airplane engines do it all
the time, usually as a result of mixture that is too rich. Granted, real
airplane engines are different and have more safety systems, but I could
not say that it is impossible, especially given the enormous variety in
types of engines, magnetos, starters, and fuel systems you see on
airplanes.

I don't see how a four cycle engine can run backwards. If the crank is
turning backwards, the intake valve would be open while the piston is going
up, pushing the contents of the cylinder into the intake manifold. While the
exhaust valve is open, the piston would be going down, sucking whatever is
in the exhaust manifold into the cylinder. there would have to be a source
of fuel in the exhaust manifold for the engine to run.

Model engines are two stroke, so they can run backwards.

A long time ago, I bought a moped (also a two cycle). The timing was so far
retarded that it ran better backwards than forwards until I had it timed. It
couldn't pull me up the hill because it ran so badly. Once, it fired up
backwards and ran great. I rode it up the hill backwards.