A Slightly Different Take On Model Making,

these are all engines based on actual ones, 

 some relatively simple like this single cylinder, taking about 2 hours to assemble the 50 or so parts, Morris Models offers six laser-cut engine DIY kits, part historical prototype and part kinetic sculpture, 

 slightly more complex a horizontally opposed twin titled “Opposed Aircraft”

  the “Wankel”

 and the “Single Cylinder” shown working in the GIF at the top of this post,

here is where things get a lot more complicated, it is a WWI Rotary Engine which includes 500 parts, and can take up to 30 hours to complete, the model was inspired by the French Clerget aircraft series that was popular in the early 1900s, for a really nice video of the engines woking, have a look here, while none of the Baltic-birch models are motorized, although the Illinois-based company says most can withstand the power of at least an 18-volt drill, Morris Models recently launched a Kickstarter campaign to upgrade its CNC cut shafting and offer more accurate designs, and you can back the project before April 5, otherwise, pick up an older kit from its online shop, what a neat set of kits for both young and old alike, I would like a few of those myself!