Some designs have two openings this one only one.
Test and assembly of a model
https://youtu.be/Ala-SnftXqs
Another basic nice setup better without the evil flywheel, doing away with ugly crank and elastic or spring is the go i say (oscillate not rotate)
In my opinion best operated with solar whatever long it takes to "pull back string of bow" to the release the build up energy.
https://youtu.be/UBQPdUC4PGE
Older model and not in English but valve operated and a lot of discussion of pressure of valve, working pressure about 25mBar (1/3 psi), runs both directions equally good.
https://youtu.be/Kpd2eHvLB04
Manson Engine Design
https://www.youtube.com/watch?v=6C41zG6ne0E
