Combustion engines power a variety of vehicles, big and small, and scale-model ones are capable of powering RC cars. These small engineering wonders feature many of the same parts and processes as a typical car engine, but it’s not a complete powertrain. A new video from JohnnyQ90 on YouTube shows the process of building a custom three-speed manual transmission that pairs with such a small engine.

The working manual gearbox connects with a Howin L4-172 Nitro RC four-cylinder engine. The four-stroke, 17.2 cubic-centimetre engine has a single overhead cam, makes 2.27 bhp (1.69 kilowatts), and features a potent and functioning water pump. It weighs 1,200 grams (2.6 pounds) and is intricate, with a reinforced crankshaft, precision-machined rocker arms and camshafts, and finished in silver and black.

The build process began by modifying the engine’s flywheel to accommodate the clutch. A 3D-printed transmission case housed the gears, hiding them from view. However, the case is modified later in the video to reveal them. Servos are added to operate the throttle and the gear shifter via remote control, and everything is then connected for testing.

It takes a bit to get the engine started, but it offered  great throttle response once it was running. There was a small coolant link that was easily fixed. It idled high, too, at around 6,500 rpm, but it reached just over 14,000 at full throttle. 

However, the transmission wasn’t perfect. During testing, the third-gear dog ring broke, which led to rebuilding the part with longer teeth. However, that wasn’t the gearbox’s only mechanical hiccup. The second-gear dog ring snapped a tooth, but it didn’t hinder the operation. It continued to function without any issues.

JohnnyQ90’s channel is filled with videos about scale-model engines, and this isn’t the first we’ve covered it. He’s previously built a two-rotor Wankel engine and a 1/10-scale model carburetted V8. Car culture extends far beyond the new metal on showroom floors, and it includes RC cars and their intricate, real-world powertrains.