It's fascinating to watch a tiny engine come together. All of the components from an full-size powerplant are there, but they're small enough to fit on a desk. Watch this 21cc inline-six come together and run.

The engine is a kit and comes with everything you need to assemble it. However, some finetuning is necessary to get things running right. The assembly follows the same steps as putting together a bigger powerplant. The first step is fitting the crankshaft into the block. Then, the pistons and connecting rods go in. This is an overhead-valve design, so the camshaft slides into the block. 

The supplied mechanical water pump doesn't work very well, so the builder hooks up a separate electric one instead. He also doesn't like the supplied cylinder head gasket and makes his own out of aluminium. There's a problem with the distributor design because the hall sensor can't fit, which requires using a rotary tool to make space.

Like a full-size engine, the work isn't done once the engine is running. The initial tune provides too rich of a mixture and the ignition timing is off. After some adjustments, the little engine sounds great. It revs quickly, and the laser tachometer shows that it can rev beyond 10,000 rpm.

The work still isn't done, though. The builder wants to fit a functional mechanical water pump. He also wants to make a new exhaust and possibly switch to a single-carburettor setup.

This builder is adept at assembling and tuning these little engines. He has also done a tiny supercharged V8. He even put together a three-speed manual transmission for a small four-cylinder powerplant.

This Howin L6-210 engine retails for $1,299.99 (approx. £1,070), but the seller is currently offering a $200 coupon. The design is inspired by the Ford 300-cubic-inch (4.9-litre) inline-six powerplant that the brand introduced in F-Series pickups for the 1965 model year, and it remained available through 1996. They were famous for producing ample torque at low revs.