This engine was built by a guy my family knows. he is an ex tool and die maker so he knows how to use a lathe and mill very well. this one is air cooled and has a 3/4" piston diameter with a 1" stroke. he has made many interesting things and is still making more.
i cant find the original video to post to embed here so hopefully this link works for you!
https://www.facebook.com/jakeimnotshure/videos/10150238356286366/
thanks for stopping by
jake