Here is some examples of single cylinder, two piston per cyl.,engines using
one combustion chamber in diesel. First one I saw was in a sub at a naval
park. I said dam, they put this engine in upside down. Little did I know
there was another piston coming up from the bottom too.

http://www.fleetsubmarine.com/propulsion.html
http://www.williamsdistribution.com/...banksmorse.jsp
http://en.wikipedia.org/wiki/Fairbanks-Morse