1958 Harley-Davidson XLCH Sportster

The 1958 Harley-Davidson XLCH Sportster was born of competition stock.

| July/August 2014

1958 Harley-Davidson Sportster XLCH
Claimed power:
55hp @ 6,300rpm (approx.)
Top speed:
883cc air-cooled OHV 45-degree V-twin, 76.2mm x 96.85mm bore and stroke, 9:1 compression ratio
Weight (wet):
480lb (218kg)
Fuel capacity/MPG:
1.9gal (7.2ltr)/40mpg (est.)
Price then/now:
$1,265 (approx.)/$7,500-$12,500

Competition improves the breed, they say. And while the 1958 Harley-Davidson XLCH Sportster was born of competition stock, its engine capacity eschewed the very type of racing its direct ancestors were designed for. How come?

To answer that, we have to go back to the mid-1930s, when racer and Motorcycle Hall of Famer Reggie Pink helped draw up the rules for production-based track racing. As he was also a British bike dealer, Pink advocated for fair competition between American brands and imports. The result was AMA’s production-based Class C, which allowed overhead valve bikes of 500cc to compete against sidevalve machines up to 750cc — or 45 cubic inches. Harley-Davidson developed the famous WRTT specifically for this class.

The K

But it was post-World War II competition from lightweight British parallel twins that motivated the Motor Company to develop a new 45-cubic-inch street bike, but still with one eye on Class C racing. The result was the Model K of 1952, a unit-construction 750cc 45-degree V-twin in a lightweight (for Harley, anyway) chassis with modern telescopic fork and swingarm rear suspension. The engine retained sidevalves for Class C homologation purposes, and the competition KRTT version ruled Class C until Dick Mann’s Grand National win on a BSA in 1963.

The Sportster XL

But in spite of a capacity increase to 888cc for the KH and KHK, the flathead K bikes couldn’t match the performance of the new overhead valve British 650s. Harley embraced the inevitable with the 883cc overhead valve Sportster, and in doing so, the company acknowledged two things: Overhead valves were the way forward, and the Sportster was not going Class C racing anytime soon. The KRTT would soldier on until Class C rules were changed for 1969, prompting the development of the Sportster-based XR750.

The Sportster was launched for 1957 as the Model XL, essentially a new overhead valve engine in slightly modified Model K running gear. The iron cylinders used a new 3-inch bore with the 3-9/16-inch stroke from the Model K — a stroke dimension that remains in all Sportsters to the present. Iron heads with hemispherical combustion chambers topped the cylinders, with valves operated by pushrods and rockers. Each pushrod had its own single-lobe camshaft, the four arranged in an arc inside the timing chest and driven by a half-time gear that also turned the ignition timer.

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