Yankee 500Z: 488cc Two-Stroke Twin Enduro

The 488cc Dick Mann-Developed Two-Stroke Twin Desert Racer and Enduro…  

In the late 1960s, before “adventure bike” was even a phrase, a small company in Schenectady, New York set out to build something radically different: a big-bore off-road twin aimed squarely at American desert racing and AMA competition. 

It was the brainchild of OSSA’s US importer, John Taylor, who envisioned a street-legal bike capable of competing in a variety of disciplines:

“With the high degree of popularity of the 500cc competition class at that time, a Yankee in each competition class was envisioned: TT, flat track, road racing and enduro machines could be built using the low, although somewhat wide, Yankee powerplant. The engine could be built using any number of cylinder porting/crankshaft configurations, which would make it one of the most flexible basic engines ever.” –Cycle World

The result was the Yankee 500Z, a motorcycle that felt almost out of step with its time — part enduro, part scrambler, part street twin — powered by one of the most unusual engines ever fitted to a production dirt machine. It was bold. It was complicated. And it may have arrived just a little too early to find its audience.

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An American Idea with Spanish Engineering

Watching the rise of desert racing and AMA competition in America, OSSA importer John Taylor envisioned a large-displacement off-road machine capable of competing in the 500cc class — something European brands had yet to fully explore. So he founded Yankee Motor Company and set out to build his dream bike, leveraging his OSSA relationships.

Rather than develop an engine from scratch, Taylor turned to OSSA’s chief engine designer Eduardo Giró to discuss the possibility of mating two 230cc OSSA single-cylinder engines in a shared crankcase to create a 500-class twin.

The result was a 488cc air-cooled parallel twin — unusual enough on its own, but even more distinctive thanks to its configurable firing order. Riders could alter the crank timing from a 360-degree to 180-degree configuration depending on how they wanted the engine to deliver power.

Meanwhile, Taylor enlisted AMA Grand National champion and motocross pioneer Dick Mann to help develop the chassis.

“Most of the initial development work in the chassis/handling department was performed by Dick Mann, who is considered by many to be the best all-around motorcycle rider in the United States… Drawing from past experience, Dick set out to make the Yankee more than just suitable; it was to be the best motorcycle of its size in the world.” –Cycle World

From the beginning, the project was something of a transatlantic hybrid:

• Engine: Designed in Spain by OSSA
• Frame and assembly: Completed in New York
• Chassis input: Influenced by American racer Dick Mann

The goal wasn’t just outright speed — it was versatility. Taylor envisioned a machine capable of tackling desert races, enduros, and (with minor modifications) flat track and TT competition in a single street-legal package…and created it.

“Taylor had produced his dream bike, one that you could ride across the state to compete in an enduro and ride home again. Said Cycle World, ‘John had accomplished exactly what he set out to do. He had updated the Triumph TR-5.'” –Motorcycle Classics

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Built Like Nothing Else

Even by early-’70s standards, the Yankee 500Z was packed with unconventional engineering choices. The 4130 chromoly frame was TIG-welded, the swingarm used oval-section tubing, and the suspension featured large-diameter forks that looked substantial compared to their contemporaries.

“Massive, beautifully constructed and rugged enough to withstand a parachute drop are terms that best describe the frame and swinging arm.” –Cycle World

The bike is often cited among the earliest off-road motorcycles to feature a production rear disc brake — a remarkably forward-thinking choice at a time when most competitors still relied on drums. Underneath the sleek tank and long seat sat one of the most complex drivetrains of any dirt bike of the era:

• Twin-cylinder two-stroke engine
• Six-speed gearbox
• Dual ignition systems and alternators
• Multi-row primary chain driving a jackshaft

The six-speed transmission, which came from OSSA’s 250cc rotary-valve single-cylinder road racer, was praised for allowing the bike to tackle everything from low-speed trials sections to 90-mph highway blasts.

Everything was built with durability and long-distance desert use in mind…though that robustness inevitably added weight.

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Adjustable Firing Order

One of the most fascinating aspects of the Yankee 500Z was its configurable crankshaft timing — a feature almost unheard of on production motorcycles of the era. Because the engine was effectively two OSSA singles paired together, riders could alter the firing sequence between two distinct personalities.

360-Degree (“Twingle”) Timing:

• Both pistons rise and fall together
• Power pulses arrive together, replicating a large-displacement single
• Strong traction feel in loose terrain
• Distinctive exhaust note and vibration character

180-Degree Timing:

• Pistons move opposite each other
• Smoother power delivery
• Higher-revving character
• More road-oriented feel

“The 360° and simultaneous firing order this mill should be considered a ‘Twingle.’ The configuration was settled upon after early 180-degree tests produced a power pulse every half revolution resulting in instantaneous power. The smooth and immediate power caused the rear wheel to break loose with the slightest nudge of the throttle.” –Motorcyclist

To support the dual-ignition system, the engine used twin Motoplat electronic ignitions and separate coils for each cylinder. This flexibility allowed riders to tailor the bike for desert racing, enduro work, flat track, or even road racing — decades before adjustable ride modes became commonplace.

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Fast, Heavy, and Ahead of Its Time

On paper, the Yankee 500Z sounded like a dream machine. Early claimed output hovered around 40 horsepower in mild tune, with period factory materials often citing 55-58 hp. In practice, however, the bike’s weight — around 158 kg (roughly 350 pounds) — made it heavier than many competitors, especially as lightweight Japanese two-strokes rapidly evolved through the early 1970s.

Period road tests praised its stability, high-speed composure, rugged construction, and status as an “instant collector’s item.” However, they also noted that the lengthy development process had left the 500Z entering a market that was changing almost monthly. 

By the time the Yankee reached broader production, Yamaha, Suzuki, and Kawasaki were introducing lighter, more focused off-road machines at competitive prices. The Yankee suddenly felt less like the future and more like a fascinating alternative path.

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Short Production Run, Lasting Legacy

Production of the Yankee 500Z lasted only a few years, with roughly 760 units built between 1971 and 1973. Currency shifts, rising costs of imported components, and fierce competition all contributed to its short lifespan. Yet despite its commercial struggles, the Yankee carved out a unique place in motorcycle history.

“Sounds like a Top fuel dragster at the drag strip sitting there idling…” -one enthusiast

Many enthusiasts and collectors today view it as an early precursor to modern big-bore adventure machines — a rugged twin designed for long-distance off-road travel long before the category existed. And perhaps that’s the best way to understand the Yankee 500Z: not as a failed experiment, but as a motorcycle that explored an entirely different vision of what off-road performance could look like.

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Yankee 500Z: Specs

Manufacturer: Yankee Motor Company (USA)
Years Produced: 1971–1973
Engine: 488cc air-cooled two-stroke parallel twin (OSSA-designed)
Power: ~40-58 claimed hp (approaching 60+ hp in full competition trim)
Carburetion: Dual carb
Transmission: 6-speed
Frame: 4130 chromoly steel
Weight: Approx. 158 kg / 348 lbs (half tank)
Brakes: Early rear disc brake application
Production Numbers: ~760 units

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