The Smallest Engine Ever To Power A Harley-Davidson
Imagine a Harley-Davidson motorcycle with an engine smaller than the Honda Minimotos of today. Sounds silly, right? Well, the smallest engine ever on a Harley-Davidson is actually smaller than the smallest engine on a Honda mini-moto today (the 109cc single of the Navi). This particular engine powered two off-beat Harley "motorcycles" of the 1960s, which were aimed at challenging the onset of extremely affordable mopeds and motorcycles from Japan, like the iconic Honda Super Cub.
There was nothing raw, rumbling, or powerful about this humble engine. It was the exact opposite of what people see as a "Harley" today. But these two 50cc bikes were cute, well-built, and had a fair sprinkle of chrome. The best part? In the '60s, these baby Harleys were the best investment as a teenager's school transport or to get someone interested in motorcycling. Here's us delving deep into how a puny engine created two fun-to-ride Harley motorcycles.
The data used to compile this article was sourced from authoritative sources, including the respective manufacturers’ official websites, a first-ride review from the 1966 issue of Cycle World, and numerous auction websites, to provide you with the most up-to-date and accurate information.
1966 Harley-Davidson Bobcat entry-level American motorcycle hd wallpaper
The Smallest Engine On A Harley-Davidson Had Just 50cc Of Capacity
This Harley-Davidson Engine Was Made In Italy
Harley-Davidson M50 50cc single engine close-up shot
The tiny Harley-Davidson engine was more Italian than American because Aermacchi made it. This was an Italian motorcycle company that Harley bought a 50 percent stake in 1960 when the American giant was undergoing financial troubles. The 49.6cc single-cylinder engine is a two-stroke unit with an undersquare (long-stroke) construction.
The compression ratio of 10:1 was commendable for the engine size and helped produce 2.5 horses. That was reasonably powerful for a 1960s motorcycle. Power was sent to the chain-driven rear wheel via a cascade-type three-speed gearbox. This transmission was hand-operated, and the shift mechanism was on the left side of the handlebar.
Engine And Gearbox Specs
Engine Configuration | Two-Stroke Single Cylinder; Air-Cooled |
Engine Displacement | 49.6cc (3.03 cu-in) |
Bore X Stroke | 1.528 X 1.65 in. (38.8 X 42.0 mm) |
Compression Ratio | 10:1 |
Power | 2.5 HP |
Torque | N/A |
Gearbox | 3-Speed; Cascade Type Handlebar-operated Shift Mechanism |
Notable Off-Beat Harley-Davidson Bikes Powered By This Engine
One Was Technically A Moped; The Other Was A "Small Bore" Motorcycle
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The humble 50cc single Harley engine was utilized in two unique offerings. The first, launched in 1965, was the Harley-Davidson M50, a moped with step-through construction designed to mimic the appearance of a motorcycle. Either way, it flaunted the "Harley-Davidson" badge. The other (called the M50S "Boy Racer") was more "motorcycle" as it had a more traditional chassis construction while still sharing the same engine. There are no differences in the powertrain layout for both these bikes. In fact, even the hardware (brakes and suspension) are the same.
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1962 Harley-Davidson Topper Side
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Harley-Davidson and Aermacchi devised well-balanced 50cc singles here. The M50 Harley had enough power to push them to a top speed of 40 mph, and the engine was efficient enough to return a claimed fuel economy of a staggering 180 MPG (that's even more efficient than the most fuel-efficient mini-moto today). Despite having a puny 1.6-gallon fuel tank, the M50 could do up to 288 miles on a full gas tank. We expect the miles to be even better on the M50S, owing to its bigger fuel tank.
The M50 Duo Are The Smallest Harley-Davidsons Ever Made
Made To Lock Horns With Dirt-Cheap Mopeds From Japan
Harley's aggressive stance in the 1960s to tackle the Japanese threat also led to the creation of the smallest Harley-Davidson motorcycles ever. The M50 duo are the tiniest Harleys ever, with a wheelbase of under 45 inches and a curb weight that literally makes them easy to lift off the ground. They were designed to be the perfect city runabouts. The dimensions mentioned here are of the M50. The M50 S specs were unavailable anywhere, but with the marginal differences between the two, we suspect the curb weight and height to be the only numerical differences.
Dimensions And Weight (Of The M50)
Wheelbase | 44.1 inches |
Curb Weight | 103 pounds |
Length | 67.8 inches |
Handlebar Width | 25.6 inches |
Height | 38.2 inches |
The hardware on these two 50cc Harleys was shared and simple. They featured a hydraulic suspension at both ends without provision for any adjustments to the preload or damping. Braking duties were taken care of by tiny drum brakes at both ends. Both had a single backbone-type frame with the engine and gearbox unit suspended forward and below the frame. Lastly, notable features that prove this include an extra bracing strut for the swing arm for additional strength and thinking cables that don't look like they will snap with the slightest pressure!
Difference Between The Harley-Davidson M50 And M50S
Main Differences Lie In Chassis Design, Fuel Tank, And Wheel Size
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As mentioned earlier, the major differences between the two are confined to aesthetics and the main frame. The M50 had a step-through chassis that classified it as a moped. But frankly, the step-through was too tiny for anyone to even "step through," as the bulbous tank and the single seat blocked the way. The M50 Sport had a crossbar that helped position the fuel tank more traditionally.
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The Sport also came with a longer two-up bench seat and different wheel sizes. The M50 came with 19-inch wheels whereas the M50S has smaller 17 inches, clearly indicating its "sporty" angle. Everything else was identical, including the lighting setup, the suspension, the breaks, and the color; the coolest color option on the smallest Harleys was a white-and-red combo, as seen above.
BONUS: The Smallest Harley-Davidson Motorcycle Engine In 2025
It Powers The Most Fuel-Efficient Harley-Davidson Today
Harley-Davidson
The smallest Harley-Davidson engine today powers the 2025 Nightster models. While it is the smallest engine today, it is by no means weak in performance. This ground-up liquid-cooled twin produces 91 horses and 72 pound-feet of torque. With a curb weight of 481 pounds (483 pounds for the two-up Special), these figures translate to commendable power-to-weight values, especially for a Harley.
The best affordable 2025 Harley-Davidson perfect for a beginner
The Affordable Harley-Davidson That’s Perfect For A First-Time Buyer
This Harley-Davidson is priced at under $11,000, making it the cheapest V-Twin cruiser from the brand.
Peak power and torque are produced higher (by cruiser standards) at 7,500 RPM and 5,750 RPM, respectively. Whereas, power is sent to the rear wheels via a 6-speed gearbox. This engine is also complemented with many technology features, including three ride modes (Rain, Road, and Sport) that help transform the riding character of the Nighster. Both the 1960s 50cc single and the 2025 975cc liquid-cooled V-twin are bold engine choices from Harley-Davidson. The prior was made to tackle Japanese rivals, and the latter is designed to take the modern and sophisticated wave of metric cruisers head-on.
Engine Specs (Nightster / Nightster Special)
Engine Configuration | V-Twin; Liquid-Cooled |
Engine Displacement | 975cc (59.5 cu-in) |
Power | 91 HP |
Torque | 72 LB-FT |
Transmission | 6-Speed |
Fuel Economy | 52 MPG |
Starting Price | $10,499 / $12,499 |
