Conjoined piston engine, with one piece ring gears.

A lot of you suggested that the ring gears should''t be split, also I went with helical gears cut in two different directions to cut down on noise and to cut down on thrust forces on the crankshaft. I realize that a one cylinder wouldn't be balanced but I'm sure someone will mention it in the comments anyway.:) A lot of you also commented that the stroke was too here you go. For assembly: you would need some sort of jig to install center pistons and ring gears before placing everything in the you could bolt on piston ends.