How does this run?

[Barnbikes]

Looks cool but how can it run? Doesn't it have pressure at both sides of the piston. I do not see a valve box.

https://minneapolis.craigslist.org/hnp/atq/5424583187.html

 

[GailInNM]

It looks like it has a semi-rotary valve on the center support shaft with the intake and exhaust on the left and right sides of the engine. Switch them for forward and reverse. The semi-rotary valve just consists of two flats on the center support shaft that are connected to the intake and exhaust ports. The pipes from the engine cylinders align with these flats to connect the cylinder ends alternately to the intake and exhaust. Just like a wobbler but with the valve sports on a shaft versus the port face. Not a common method these days but not unique.
Gail in NM