Against All Odds: 1971-1972 Yankee 500Z

Comparing the Yankee 500Z and its main competitors, the Husqvarna Baja Invader 500 and the BSA B50SS Gold Star.

| November/December 2016

  • Yankee 500Z.
    Photo by Phil Aynsley
  • 1969 Husqvarna Baja Invader 500.
    Photo by John Ker/Motocross Action Magazine
  • 1971 BSA B50SS Gold Star.
    Photo by Robert Smith

Yankee 500Z
Years produced:
40hp @ 6,500rpm (claimed)
Top speed:
488cc (72mm x 60mm) air-cooled 2-stroke parallel twin, 9:1 compression
Transmission :
Dry clutch, 6-speed gearbox, chain final drive
349lb (w/half tank fuel)
Price then/now:

Motorcycle entrepreneur John Taylor was nothing if not persistent. His continual cajoling of Spanish motorcycle makers led to some of the best small bikes sold in America; and to Taylor’s personal dream machine, a big enduro bike that anticipated the dual-sport boom by a quarter century.

As U.S. importer in the early 1960s, Taylor persuaded Bultaco to produce the 200cc (later 250cc and 350cc) Matador street-scrambler for the U.S. market. He even came close to owning the CEMOTO/Bultaco factory in Barcelona. But what he’s best known for is the 500cc twin-cylinder dual-sport bike that was made in America and bore the brand Yankee.

Challenges ahead

Taylor needed all his persistence to bring his bike to market. First shown to the press in 1967, the Yankee 500Z took another four years to get into production. No doubt OSSA (the small Spanish firm contracted to make the Yankee drivetrain) were distracted by their own Grand Prix ambitions, and by the death of their star rider, Santiago Herrera, at the Isle of Man TT. Then once production started, Yankee was hit by the Nixon administration’s decision to abandon the gold standard, which devalued the dollar, doubling the import price of the OSSA powerplant. Lesser men would have quit, but Taylor pressed on with his state-of-the-art design.

The starting point for the Yankee was a TIG-welded chrome-moly steel tube spine frame designed by Dick Mann. (“Massive, beautifully constructed, and rugged enough to withstand a parachute drop,” said Cycle World.) A stout (by 1967 standards) 42mm diameter Telesco fork was gripped by alloy triple clamps forged by none other than Smith & Wesson. Teflon-coated bronze bushes attached the heavily triangulated swing arm at the rear, supported by dual five-way-adjustable Telesco shocks. The tires were 4.2 x 18 inches at the rear and 3.15 x 21 inches at the front running on Akront alloy rims. Complementing the 6-inch drum front brake was a 9-inch hydraulic rear disc, which offered many off-highway advantages over a drum — self-cleaning, effective when wet and unaffected by suspension travel.

The 488cc (72mm x 60mm) piston-port, 2-stroke twin engine was mounted forward in the frame for Taylor’s preferred weight distribution. Built to Taylor’s specification, the engine used two OSSA Pioneer pistons, cylinders and heads, with two separate crankshafts running on ball bearings and connected by a central sprocket. The cranks were spaced at 360 degrees, meaning both cylinders fired together. (Taylor anticipated also using the engine for road racing, and the cranks could be reset to a 180-degree interval if necessary.) The central sprocket drove a 6-speed gearbox by gear from a chain-driven jackshaft and 12-plate dry clutch. A pair of 24mm IRZ 4G dual-needle carburetors fed the engine, which exhausted through a Hooker Headers muffler under the engine with dual pipes and Krizman spark arrestors. The electrical system was powered by two Motoplat alternators, one on each side of the engine unit: a 6-volt output ran lighting and accessories, while electronic triggers fired two separate ignition coils — to facilitate the 180-degree firing interval option.

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.”

Contemporary reports acknowledge the 500Z’s quality components and ruggedness, while praising the engine’s ample torque, broad powerband, and slick-shifting 6-speed gearbox. “The 500Z will do some things that a 250 bike just won’t do — like climb a long, rough hillside in fourth gear at half throttle,” said Cycle. “It was built to deliver a stable, comfortable ride on rugged trails; to let the rider use engine torque rather than muscle power in getting the bike where he wants it to go. The machine did just that.”

Unfortunately, the world had moved on. The preferred enduro tool was now a nimble 250-pound, 250cc 2-stroke single, not a 335-pound 500cc twin. After building around 760 units, production of the 500Z ceased. Taylor revealed a lighter 2-stroke single for 1973 using a 460cc Motosacoche engine, but the project was stillborn. Perhaps Taylor was just 20 years ahead of his time. MC

Contenders: More big offroaders

1969 Husqvarna Baja Invader 500
Year produced:
60hp @ 6,500rpm (claimed)
Top speed:
110mph (approx.)
490cc air-cooled 2-stroke parallel twin
4-speed, chain final drive
300lb (approx., Baja trim)

Like Taylor, Husqvarna engineer Ruben Helmen thought a double-barreled dirt bike might be an offroad success. In 1966 he designed a 2-stroke twin using two 250cc top ends on a common crankcase. The engine was mounted in a Husqvarna frame with 35mm Husky front fork and dual Girling rear shocks. The wheels were a 21-inch in the front and an 18-inch rear on Akront alloy rims with drum brakes. Testing confirmed that the bike was fast, but too bulky for FIM 500cc motocross competition. However, a 504cc version dominated the less competitive heavyweight (501-750cc) division in 1969. Reconfigured to 490cc, the sole complete machine was shipped to U.S. importer Edison Dye, who entered it in the 1969 Baja 1000 with Gunnar Nilsson and J.N. Roberts as riders. The Husqvarna won the motorcycle class by 20 minutes!

So why didn’t Husqvarna put the 500 into production? A new transmission would have been needed, as the stock box was “marginal,” according to Nilsson. Also, a new crop of powerful 500cc 2-stroke singles meant that twins had no future in off-road competition. Check out the sole Baja Invader ever built at Tom White’s Early Years of Motocross Museum in Villa Park, California.

1971-1972 BSA B50SS Gold Star
Years produced:
34hp @ 6,200rpm
Top speed:
80mph (est.)
499cc air-cooled OHV single
4-speed, chain final drive
310lb (dry)/45-55mpg
Price then/now:
$1,300 (est.)/$2,500-$4,500

BSA’s B50 engine was also intended for competition. And it performed well, with “Big John” Banks placing second in the FIM World Motocross Championship in 1968 and 1969 on the factory B50MX. This racing development work led directly to the street scrambler B50SS.

The B50 engine was a full 499cc with a strengthened, 3-main-bearing bottom end and a beefier transmission. The engine went into an oil-bearing frame derived from the factory motocross bikes, featuring a tubular swingarm with a cam adjuster at the needle-roller pivot — ideas that BSA borrowed from the Rickman brothers.

Completely revised electrics, ancillaries and bodywork were well designed and worked well, though the TLS drum front brake was underwhelming.

Author Steve Wilson owned a B50, and describes his experience in BSA Motor Cycles Since 1950: “… for short haul, stop-and-go motoring, the engine’s punchy power characteristics made for an inspiring, pant-kicking, arm-wrenching ride … the B50’s engine clatter, plus the vibration from such a powerful engine in a comparatively light frame did make long-distance riding a bit of an ordeal.”

5/31/2019 11:31:13 AM

I got my buddies new Yankee Twin stuck in "a puddle" in the summer of 1971. When I got it out of the "puddle" last week, everyone had already gone home. Go figure...

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