Ironhead Sportster (1957-1971)
When Harley-Davidson bolted their new OHV motor to the K-Model frame in 1957, the Sportster legend began. The XL motor displaced 883cc (advertised as 900cc) derived from a 3.81" stroke and a 3.00" bore. Both connecting rods shared a common crank pin, referred to as 'knife and fork' design. Each valve was operated by it's own cam, simplifying valvetrain geometry. One carburetor fed both cylinders. The bottom end was the same as the K-Series bike - inside the rear of the engine cases housed the four-speed transmission, with twin cylinder jugs sitting 45 degrees apart. The new overhead-valve engine, fitting neatly under the gas tank, sported a pair of cast-iron cylinder heads.
Aluminum is usually the preferred material for cylinder-heads; not only is it lighter than cast-iron, it dissipates heat better. Harley had previously used aluminum heads on their Panhead motor (introduced in 1948), which helped reduce engine operating temperatures in warm weather. But early Panhead riders were experiencing top-end problems, so H-D engineers chose to use cast-iron for the Sportster heads. In its first year, concerns of overheating kept the compression ratio at a conservative 7.5:1. Making 40 horsepower and weighing 495 pounds, the new XL Sportster was not yet burning up roads.
In 1958, the XL remained the standard Sportster, while the new XLH model was fitted with larger valves and higher, 9:1 compression ratio. Power increased significantly. A third model, originally set up as an off-road bike, was named the XLCH. It was sold with no headlight or taillight and had twin straight exhaust pipes. A small 1.9 gallon gas tank, borrowed from the 125cc Hummer, would become the classic Sportster 'Peanut' tank.
The XL model received new fenders and headlight nacelle, and an ignition switch mounted on the left fork. Saddlebags, available in either white or black, were optional. The XLCH model proved quite popular, and in 1959, lights, mufflers, and full fenders were fitted. The left-handgrip spark advance was still retained. A smaller 5-3/4" headlamp with eyebrow was used, and would become a classic Sportster feature.
Built to compete in TT scrambles, Harley-Davidson started producing the XLR in 1962. Differences between it and the XLCH were mostly engine modifications; different heads and cams were used, and ball-bearings were used at the crankshaft ends to reduce friction. Produced in limited quantities, the XLR weighed about 300 pounds and properly tuned, could put out 80 horsepower. The motor would power many race-bikes, including Cal Rayborn's record-setting streamliner in 1970 (see below).
Sportsters In The Sixties
Sportster models through the early Sixties remained basically unchanged, receiving small, yearly refinements. In 1963, an ignition key was fitted to the XLCH. Popular options included turn signals, spotlights, and windscreens. In anticipation of upcoming electric starters, both the XLH and XLCH were upgraded to 12-volt electrical systems in 1965. Sportsters now had automatic spark advance, which helped starting.
The classic oval-shaped "ham-can" air cleaner, brought about by federal emission laws, first appeared in 1966. Also this year. the Linkert carburetor was replaced by a Tillotson, which was less sensitive to lean and tilt, and also helped power and driveability. Engine cases were revised to accommodate electric start, first offered in 1967. Two years later, cylinder-heads were redesigned, and had larger valves.
In 1969, Harley-Davidson was acquired by AMF (American Machine and Foundry Company), a large business conglomerate who manufactured and sold, among other things, lawn and garden equipment, golf clubs, snowmobiles, sailboats, powerboats, bicycles, mopeds, and now, motorcycles.
"Then Came Bronson" Bike
1970 was the second and final season of the American TV show "Then Came Bronson". The show starred wool-capped Michael Parks riding around the country, finding adventure on his red '69 Sportster XLH. Bud Ekins, the famous Hollywood stuntman, appeared in several episodes. The show and the bike were both popular, prompting Harley-Davidson to offer a "Bronson Red" paint option for several years.
Sportster-powered Bonneville Record-Holder
The Bonneville Salt Flats in northwestern Utah have long been a mecca for high-speed competition. It was here that a Sportster-powered streamliner motorcycle broke the world speed record in 1970. The streamliner body was a 15-foot-long aluminum tube, with a cross-section of only 23 inches. Inside was a small cockpit and a modified XLR motor, bored and stroked to 1,480cc (89-cubic inches). The engine ran on 70 percent nitro-methane. Owned by Manning/Riley/Riveria, the pilot was famed Harley-Davidson factory rider Cal Rayborn. His recorded speed of 265.492 mph would stand for fifteen years.
The Sportster's distributor, formerly sitting atop the right-side engine case, was moved inside the gearcase, and an automatic advance mechanism was added to aid starting. 1971 was also the first year of the wet clutch setup. The fiberglass seat and tail section known as the 'boat-tail', offered last year, was available again this year for the final time.
Now in its 14th year, an average of 6,500 Sportsters were being sold annually - triple the amount from a decade ago. And in that time, the Ironhead XL's fan-base had widened deeply. On one end were the race guys, who loved its tourquey power and the endless ways to squeeze out more. And on the other end were the custom guys, who embraced the clean, integrated symmetry of the compact V-twin engine.