An internal combustion engine with a flathead layout is the type of simple, yet robust design you'd find in a Ford Model T and lots of other early automobiles. In this video, the YouTuber JohnnyQ90 builds a tiny, yet fully functional example and showcases the entire project.

Where just about all modern combustion engines put the valves above the cylinders, a flathead put them on the side. This is why some folks call this design a sidevalve.

The tiny engine displaces just 17.5 cubic centimetres (1.06 cubic inches) and weighs 1.5 kilograms (3.31 pounds). It runs on petrol, just like a full-sized flathead. There's even a functioning carburettor.

The build process includes everything you'd be doing to put together a flathead engine, except the parts are far smaller. It's like building a model car, but in the end, you have a fully functional engine.

Assembling the pistons involves a vice to fit the wrist pins through the connecting rods. There are even tiny piston rings to install.

The valvetrain is even more complex to build. The process includes keeping the valve lifters to certain tolerances.

After a majority of the assembly, the video cuts to a point where the engine has the fuel, coolant, and oil lines in place. Upon initial startup, the engine sounds like it's running pretty rough. Also, one of the front seals is leaking oil.

By the end, the engine is purring along. The sound is reminiscent of a tiny weed trimmer. Unfortunately, there's bad news because the starter motor fails. Judging by the assembly process, replacing the part doesn't seem too complicated.

The kit to build this engine retails for $999.99, but a discount for the first 50 buyers takes the price down to $799.99. This person also has the $149.99 accessory collection that includes the starter spark plugs, radiator, and more.

We previously saw JohnnyQ90's work when he built a miniature, two-rotor Wankel engine that revved to 18,000 rpm and sounded amazing. He also assembled a nitro-fuelled, 1/10-scale V8 with a pair of carburettors.