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Pre-Order NowAir-Cooled · Hit & Miss · Ready to Run
A 1910s farm engine, built for your desk
A working miniature of the little air-cooled Chore Boy, the engine that did the chores on American farms and, under the Amanco name, on British ones too. Belt-driven fan, finned cylinder, glass drip oiler and twin spoked flywheels. It arrives assembled and ready to run.
On the farm, engines like this were mounted on small wheeled carts and pulled from job to job: to the well, the woodpile, the barn. At engine shows today, that's still how collectors display them. The ST-02 gives your B04 the same look.
Engine and cart together for less than the B04's regular price.
Add the ST-02 Cart →✦ ✦ ✦
Before power lines reached the countryside, a small engine like this was the hardest worker on the farm. Built in the American Midwest in the 1910s, these little "chore" engines pumped water, ground feed, turned cream separators and sawed wood, day after day, for families who couldn't afford a hired hand.
They weren't fancy. They were plain, honest machines, but they started, they kept running, and they cost far less than the big engines of the day. For many families they were the first taste of mechanical power. Thousands crossed the Atlantic to work on British farms, where they earned the same loyal following.
The air-cooled versions were especially practical. With no water hopper, there was nothing to freeze in winter and less weight to carry around the yard. Cooling fins and a small belt-driven fan did the job instead.
"Pop… whoosh, whoosh… pop."
To many people, that is the sound of a grandparent's farm.
A century later, the farmers are gone but the engines are not. Collectors restore them and run them at shows, and they remain among the most collected vintage engines in the UK. The B04 brings that sound to your desk.
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A hit-and-miss engine has no throttle. When the flywheels spin fast enough, the governor holds the exhaust valve open and the engine coasts without firing. That's the "miss." As the flywheels slow, the valve closes and the engine fires again: the "hit."
Out of the Box✦ ✦ ✦
The B04 arrives fully assembled on its hardwood base. No building, no adjusting. Add fuel, oil and a battery, give the flywheel a flick, and hear it run.
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| Model | OKMO B04 |
|---|---|
| Engine type | Horizontal single-cylinder, 4-stroke, hit-and-miss |
| Inspired by | 1910s air-cooled Chore Boy (sold in Britain as Amanco) |
| Displacement | 3.6 cc |
| Bore × stroke | 16 mm × 19 mm |
| Speed range | 500–3,000 rpm |
| Cooling | Air-cooled: cylinder fins + belt-driven fan |
| Ignition | Mechanical contact igniter + CDI |
| Ignition power | 1 × AA 1.5V battery |
| Lubrication | Adjustable glass drip oiler + oil mixed in fuel (splash lubrication, no oil pump) |
| Fuel | Gasoline, 92/95 octane or higher |
| Engine oil | 2T or 4T engine oil, mixed into the fuel |
| Fuel-to-oil ratio | 25:1 – 30:1 |
| Starting | Flick the flywheel quickly by hand (clockwise), or use an electric drill with the starting rod |
| Power output | Belt pulley |
| Main material | CNC-machined metal |
| Dimensions | 225 × 115 × 130 mm |
| Assembly | Ready to run (RTR), fully assembled |
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The B04 is now open for pre-order, with $100 off during the pre-order period. Pre-order runs until December 1, 2026. The B04 is currently in production, and orders are expected to ship by December 10, 2026. Follow Stirlingkit for production updates.
Yes. The B04 arrives fully assembled and ready to run, so there's nothing to build or adjust. That makes it a great choice for beginners. Just add fuel, oil and a battery and follow the manual for the first start. Like any real engine, it may take a few tries to get the fuel setting right the first time. That's normal, and part of the fun.
The OKMO B04 engine, fully assembled on its hardwood base, and the user manual. Not included: AA battery, gasoline and engine oil.
While it runs: with no water jacket, long high-speed runs build heat, so run it in sessions and feel the cylinder temperature. The exhaust gets very hot. Run it in a ventilated space away from anything flammable. After running, top up or drain the drip oiler.
Yes. The ignition contacts are in plain view, so wear, oil build-up or a changed gap can be spotted by eye and fixed by hand.
It is a miniature inspired by the 1910s air-cooled Chore Boy (Amanco in Britain). To stay as close as possible to the original, it recreates these details:
Some details, such as the hardwood base and battery box, are designed for desktop display.
Yes. The belt pulley lets the B04 drive small accessories, such as the optional vintage-style vertical water pump. For a classic show-yard look, you can also mount it on the ST-02 steerable engine cart.
American farm engine makers named their engines after the help they replaced. The Chore Boy did the odd jobs, and the Hired Man did the heavy work. Together they show the two ways early farm engines kept cool: the B04 with fins and a fan, the B03 Hired Man with a water hopper.
Both are built on the same 3.6 cc platform at the same size, so they make a matched pair on the shelf, a small piece of American farm history side by side.
B04 Chore Boy (pre-order)
B03 Hired Man (pre-order)$100 off each engine, applied automatically at checkout.
