WARNING This is only for unconventional engines... If it looks like it will seize up... not ever start... overheat... fall apart... is impossible to service it belongs here... otherwise it does not! If it looks, sounds or works like a CAT, Mann or DDMTU do not post it here...
Paut Motor This looks promising... some of the pistons act as air pumps for the others... no rods... reciprocating crankshaft... yes the whole thing reciprocates... https://www.youtube.com/watch?v=HFUsnKJtMYQ
Yes... and you would like machining kugelmotor cylinders??? too. I cannot imagine how they build it but apparently it exists.
This is "engine" was designed by electrical engineers... runs without gas or diesel fuel https://www.youtube.com/watch?v=uhYEdD94vH0
Too Funny. The builder stated that it is capable of powering an LED. also, here's one that adheres to the OP's requirements: https://www.youtube.com/watch?v=V2bwevLgeRc
Unconventional engine My little self launching glider aircraft has an retractable rotary (Wankel) engine. 56 HP, runs on normal unleaded gasoline, is very small, lightweight and the most amazing thing on this Wankel engines is, with increasing RPM the vibrations go towards NIL and the engine sounds like a little turbine. As this engines are used only during take off for max. 5 to 10 min per flight and I am only doing app. 30 to 50 flights a year on this glider, it will last virtually for ever. During the no fly winter season, the engine is taken out of the a/c within 10 min. and send in a box to the aircraft manufacturer for anual service and certification. In the springtime the engine is put back in again and the glider is ready to fly. Pure fun!!! Wankel engines are great aircraft engines, because of their small size and low weight and their remarkable low level of vibration. And IMO, they would make great outboard engines for boats. To bad, this engine principle is not really usable for self igniting fuel (Diesel).