Walter Villa aboard the world championship-winning Harley-Davidson RR250.
What’s this, a Harley-Davidson with – gasp! – expansion chambers, not extended fishtail pipes? And no ape hangers or chromed everything to be seen anywhere? Well, yes, and this particular Harley-Davidson, the RR250, happened to win four Grand Prix World Championships, all with famed Italian racer Walter Villa on board as he topped the 250cc class in successive years, 1974-1976, his fourth title coming in the 350 class with an engine bored and stroked to 347cc. Think of Signore Villa’s 1976 double as a special Bicentennial memento to America’s premier motorcycle marque.
Harley’s path to four world championships is rather interesting, the journey starting in 1960 when the Milwaukee-based company purchased 50-percent interest in the motorcycle division of Italian company Aermacchi. The union gave Harley immediate access to Aermacchi’s small-bore bikes including the Ala D’oro, a model powered by a single-cylinder 4-stroke 250cc engine.
U.S. race fans might remember it as the Sprint, a bike used by Harley-sponsored racers back in the 1960s for competition on short track ovals and in AMA lightweight road races. The Sprint was a worthy bike, but severely outgunned by 2-strokes, especially Yamaha’s twin-cylinder bikes of the era. But as the saying goes, “If you can’t beat them, join them,” so Aermacchi developed a twin-cylinder 2-stroke of its own. Starting in 1971 with a pair of 125cc air-cooled cylinders from a motocross race bike, engineer William Soncini created the company’s first road racing 250 twin. The bike was ready for the 1972 GP season, and veteran racer Renzo Pasolini piloted the new Harley to three wins, ultimately losing the championship by a single point to Finnish rider Jarno Saarninen and his Yamaha. Sadly, both riders lost their lives in a horrific crash during the Italian GP at Monza the following season. By 1974, Harley had purchased full rights to Aermacchi’s motorcycle division, and called on Villa to be its No. 1 rider.
Villa tucked in aboard the RR250.
Aermacchi later shaved off the engine’s cooling fins to wrap the cylinders and heads with water jackets for better cooling, which allowed for more compression and more power. The RR250 ultimately produced a claimed 53 horsepower. Increasing bore and stroke to 64mm x 54mm upped displacement to 347cc for a 350-class entry, and variations of a 500cc engine were tried as well, one with four carburetors feeding a pair of cylinders! More fuel and air into the engine, reasoned engineers, meant more horsepower to the rear wheel. But as Allan Girdler explained in his book Harley Racers, “It was easier and more efficient to double the number of carbs when the displacement doubled [over the RR250’s], than to find a pair of carbs twice as big.” No matter, the RR500 never enjoyed the success of the RR250 or RR350.
Meanwhile, here in America, Harley’s factory rider Gary Scott startled the AMA establishment when he paced the field during the 1974 Loudon Lightweight race to score the sole RR250 win for Harley’s home crowd. In 1978 Harley sold Aermacchi to restructure the company, in the process giving full attention to extended fishtail pipes and chromed everything.
– Dain Gingerelli