Playing in the Dirt: 1974-1978 Harley-Davidson SX250

The Harley-Davidson SX250 was created to counter the Yamaha DT-1 during the offroad bike craze in the 1960s.


| January/February 2016



Harley-Davidson SX250

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Image courtesy Harley-Davidson

When the lightweight offroad bike craze hit the U.S. in the late 1960s, Harley-Davidson was perfectly positioned to compete. But H-D’s dirt diggers didn’t hail from Milwaukee — or anywhere else in the U.S.

In 1960, Harley bought a 50 percent stake in the cash-strapped Italian motorcycle company Aermacchi. Parent Aeronautica Macchi had spun off its motorcycle division to focus on its core business: aircraft. Based in their old seaplane factory on Lake Varese north of Milan, Aermacchi produced a sturdy but rather staid overhead valve 4-stroke single that became the H-D Sprint in the U.S.

Offroad bikes were quickly growing in popularity in the 1960s U.S. market, so when Yamaha turned the dirt bike world upside down in 1968 with the 250cc DT-1 (selling as many as 50,000 a year by the early 1970s) other makers were bound to follow. For 1969, Harley offered a high-pipe version of the Aermacchi-built 125cc Rapido, but it was no offroad machine. Aermacchi Harley-Davidson’s first real counter-offering to the DT-1 came five years later with the 1973 SX125, followed quickly by the 1974 SX175 and finally the SX250. The SX175 and SX250 were essentially identical apart from the 250’s larger cylinder bore.

Like the DT, the SX250 was powered by an air-cooled, 2-stroke, single-cylinder engine with oil injection. A 32mm Dell‘Orto PHB32 carburetor fed the piston-ported, chrome-plated cylinder, while a capacitive-discharge ignition provided sparks. Drive to the wet multiplate clutch was by gears, and a 5-speed transmission and chain to the rear wheel completed the drivetrain. The engine fitted into a dual-cradle steel tube frame with a Ceriani-style front fork and swingarm rear controlled by a pair of spring/shock units with five adjustable preload settings. Tires were 3.25 by 19 inches front and 4 by 18 inches rear.

Though conventional in most ways, the SX250 incorporated a number of useful features. The ignition system was independent of the battery, so the engine could be started and run without one. The swingarm used snail cam adjusters (a scheme pioneered by Rickman Motorcycles in England), making it easier to accurately set rear wheel alignment in the field. Equally practical was the quick-detachable rear wheel for fast tire repairs. Oil for the pressure-fed lubrication system was carried in the top frame tube; and the kickstart lever drove through the primary, meaning the engine could be started in gear — a real boon in the dirt.

The result was a machine that could be made competitive in offroad events with the right upgrades. Enduro legends Larry Roeseler and Bruce Ogilvie used a highly modified SX250 to win the motorcycle class in the 1975 Baja 500, recording Harley-Davidson’s only win ever in that event.

MONTYB
1/21/2016 8:44:51 AM

Larry Rosseler and Bruce Ogilvie raced one of these HD's back in 1975 Baja 500! Amazing fact, and makes me feel oh so old!






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