Harley began manufacturing motorcycles in 1903 and introduced the Sportster in 1957. Since then, the Sportster has been in production without a break for the last 50 years, making it the record holder for a continually produced vehicle in America. It even beats out the iconic Chevy Corvette for top honors, since the Vette missed a year of production in the early ’80s. Within a year of its debut, the Sportster became known as the first of the “Superbikes” and one of the company’s most enduring models.

Looking back 50 years, the launch of the first Russian Sputnik was on the horizon, ’57 Chevys were “in,” and Elvis and rock ‘n’ roll music were cool. But the origins of the Sportster go back way beyond that, all the way to the 1929 model, a 45-cubic inch middleweight that would later become known as the Flathead. During the ’30s and early ’40s, the Factory had enormous success racing various models of the 45-cubic inch flathead. In 1946, Harley-Davidson introduced the 45-cubic inch Flathead WR racing motorcycle, which proved to be one of the best racing motorcycles ever built. In 1952, the W models were replaced with the revered 45-cubic inch side-valve K series. The new K-models included an integrated four-cam engine and four-speed transmission design, along with foot shift, swingarm rear suspension, and telescopic front forks to compete with smaller, sportier motorcycles coming mainly from Great Britain.

Over the next several years, Harley-Davidson improved upon the 45-inch K-model, including stroking the Flathead engine and increasing displacement to 53.9 cubic inches (883cc). Harley sold the hopped-up new model as the 55-cubic inch KH (H for Hot), believing that 55 cubic inches carried greater marketing cache than either 53.9 cubic inches or 883cc. However, the modestly powered K was still being out-powered by cheaper, high-revving 40-inch British imports, so the Factory knew it needed a more powerful middleweight engine.

In the mid-’50s, Detroit auto makers were transitioning from Flathead to overhead valve (OHV) technology, so Harley engineers decided to follow suit and designed the new model with overhead valves while incorporating engineering of the W-model and retaining the K-model’s integrated engine/trans and four-cam design. As such, the Sportster XL was born with cast-iron OHV cylinder heads and aluminum rocker boxes that eventually led to the Shovelhead engine design in 1966. Rumor has it that the genesis for the XL moniker was spawn from the name “Xperimental Lightweight.”

The objective for using an overhead valve design on the Sporty was to improve cylinder filling and power. With OHVs, the valves are located in the cylinder head and positioned above the cylinder. A valve opens by moving downward toward the cylinder, providing the air/fuel mixture a rather direct and downward path into the cylinder for improved filling. On the other hand, with a Flathead (also called side-valve) engine, the valves are not in the cylinder head; instead, they are located beside or directly to one side and parallel to the cylinder and move upward during opening. This arrangement requires the air/fuel mixture to make two 90-degree turns to either fill or exit the cylinder, which is much less efficient than with an OHV engine.

Although the new OHV Sportster engine and older side-valve KH engine were both rated at 883cc or 53.9 cubic inches, Factory engineers destroked the Sporty from the KH’s 4-9/16 inch stroke to 3-13/16 inch. To maintain the same displacement with a shorter stroke necessitated increasing the Sporty’s bore to 3.00-inch from the KH’s previous 2.75-inch. The Sporty’s shorter stroke and larger bore allowed the use of bigger valves while producing a higher revving engine with lower piston speed at any given rpm.

The Sportster’s new cast-iron heads were designed with deep hemispherical combustion chambers, similar to WWII aircraft engines. The hemi-style chambers allowed for big, high-flowing valves, but also required heavy high-dome pistons for high compression. Heavy pistons make balancing an engine more difficult, while high piston domes impede cylinder airflow during valve overlap and interfere with flame travel during combustion. Note that in the ’80s, both the Evolution Sportster and Big Twin engines were designed with lightweight flattop pistons and shallower combustion chambers to minimize the inherent drawbacks in the original Ironhead Sporty. The ’57 Sportster XL was shipped with a rather conservative 7.5:1 static compression ratio (for an OHV engine). Two years later, the compression was upped to a more reasonable 9:1 ratio.

The XL’s aluminum pistons connected to Harley’s typical “knife-and-fork” design, connecting rods riding on a single-throw crank with heavy counterweights. The four camshafts were a carryover from the K-model and provided straighter pushrod angles (and more accurate valve timing) than with a single-cam design. Solid roller tappets rode on the cam lobes and transmitted valve timing to the rocker arms via steel-tipped aluminum pushrods. The ’57 Sporty cylinder heads shipped with relatively small valves, but valve sizes were increased in ’58.

The integrated engine/transmission design made for a very compact yet rigid drivetrain that was several years ahead of the British bikes. A robust triplex primary chain connected the crank to a dry clutch, which was a carryover from the K-model, as was the four-speed transmission, right-side secondary drive, and right-side foot shift. A heavy cradle-style frame rolled on narrow 18-inch spoked wheels, while narrow drum brakes served as binders for stopping.

A Linkert DC carb with a front-mounted float bowl (not the brass M-53 Linkert on the K) was fed gas from a 4.4-gallon fuel tank. Instruments were sparse on ’57 XLs, including only a nacelle-mounted speedometer. However, a hand-actuated fork dampener for minimizing wheel wobbles was standard equipment on the front fork.

The Sportster XL was a rudimentary hot rod with a solo seat designed to take on the British imports. To that end, options were sparse and primarily limited to a sport windshield, rear luggage rack, buddy seat, fiberglass saddlebags, and chrome package.

In 1958, XL models shipped with low compression motors, but the new XLCH (CH for Competition Hot) came with larger valves and high-dome 9:1 compression pistons. Simply put, the XLCH was a stripped-down, lightweight Sportster with straight pipes, scanty fenders, no lights, magneto ignition, and a 2.25 gallon “peanut” fuel tank. The Fairbanks-Morse magneto often made kick-starting the Sporty an adventure rather than a routine procedure, partially because a magneto throws a weak spark at low engine rpms and partially because the mag had no provision for setting an ignition advance curve. Early Sportster models required the magneto be set to full advance 100 percent of the time, about 45 degrees BTDC, which frequently caused the engine to kickback unless a hefty and precisely timed effort was placed on the kick starter. A wimpy or hesitated effort, especially with a hopped-up motor and lightweight kicker, often resulted in the kicker being tossed onto the handlebars, or even worse, a sprained ankle. Luckily, XLH owners had a large 6v battery and points system for firing the ignition.

The overall theme of the ’58 models was that the street-oriented XLH came adorned with more sheetmetal and accouterments than the off-road and hot rod-based XLCH. To keep mud and road debris off the rider, XLH models had larger, deeper, and more robust fenders than the skimpy bobbed versions embellishing the XLCH. All ’58 XLHs shipped with 18-inch wheels and 3.50-section of rubber on both front and back, while the XLCH was shod with 3.25×19 rubber on the front and 4.00×18 on the backside. The headlight on the XLH was chrome and rather large, patterned somewhat after the larger FL-series bikes. In contrast, the XLCH’s headlamp was bare bones and usually painted. A robust cast-aluminum primary cover enclosed the triplex primary chain and clutch basket on XLH models, while CHs shipped with a lighter stamped-steel cover. And any CH owner wanting to fend off Triumph Bonnevilles opted for the racy dual-exhaust option.

For 1959, XLHs came fitted with a nacelle-style headlight and dual exhaust. And as the years progressed, Sportster models evolved with more and more improvements. After 1959, the next major milestone year was probably 1965, when the XLH and XLCH were delivered with a 12-volt generator and electrical system. That year, the XLHs used two 6-volt batteries wired in series and didn’t get a 12-volt battery until the next year. 1966 also saw the Tillotson diaphragm carburetor and so-called oval “Ham-cam” air cleaner replace the Linkert DC and its traditional round air cleaner assembly. Although developed earlier, “P” cams also became available. In 1967, electric start became an option. A combination of kick- and electric-start options remained in effect until 1980, when all models shipped only with electric start.

The Sportster was fitted with new cylinder head castings and port shapes in 1969. That was also the last year for a magneto ignition on the XLCH. 1971 saw the introduction of the single-spring wet clutch, and in 1972, the 883cc (55 cubic-inch) engine was replaced with the 1000cc or 61 cubic-inch engine by increasing bore size 3/16-inch to 3-3/16 inches. The new engine had 9:1 compression and was rated at 61 horsepower, which allowed the CH to rip off low 13-second quarter mile times at around 98 mph.

About that same time-actually a few years earlier, in 1970-the AMA modified the rules for Class C racing to allow for 750cc overhead-valve engines. That led the Factory into developing the new Sportster-based XR-750. The OHV XR-750 would replace the venerable side-valve KR 750 racer. The XR-750 is a de-stroked Sportster engine with twin carbs and all-new internal components. The 1970-71 models shipped with iron heads and cylinders, but was only a stopgap measure. In 1972, a new, more powerful, more reliable aluminum alloy XR-750 debuted and became the dominant dirt track racer through the next three decades.

The early to mid ’70s saw an influx of fast European and Asian imports that were equaling or even surpassing the Sportster’s performance. That fact and the sale of Harley to AMF seemed to change the Sportster’s market position from one of a mean streetfighting hot rod to only a middleweight bike filling a product line niche.

At least, that was until the introduction of the Evolution Sportster in 1986. The new aluminum-based Evo Sportster engine opened the doors to Factory and aftermarket performance parts that again made the Evo Sporty a formidable street-fighter and racer, especially when engine displacement was bumped into the 100-plus cubic-inch range.

For anyone interested in getting a burst of adrenaline from the latest Sporty streetfighter designed for the new millennium, checkout the XL 1200N Nightster. With a wicked combination of styling, stance, performance, and bad-boy attitude, the Nightster has a gritty, urban feel offering an exhilarating ride.

And while you’re at it, don’t forget the new 50th Anniversary Sportsters that honor the family heritage with a special 1200cc model. With new Electronic Sequential Port Fuel Injection (ESPFI) system, new gauges, and “50th” tank emblem, the 50th Anniversary Sportster pays tribute to a legend in the tradition of previous commemorative Harley-Davidson models. See for yourself why there are few motorcycles as enduringly popular as the Harley-Davidson Sportster.

Sportster Milestones

1957 Sportster XL 883cc, 7.5:1 CR Introduction 1957-65 Linkert DC Carb 1957-66 Kick-start 1957-71 Early-style barrel oil pump 1957-77 Original cradle frame 1958 9:1 CR, larger Valves 1965 12v Generator 1966-71 Tillotson Carb 1967-79 Electric Start option and/or kick start 1969 Last Magneto Ignition 1969 New Cylinder Head Casting 1970 Distributor-only Ignition 1971-early 78 Points & Mechanical advance Ignition

1971 1st Cone-style Ignition gear cover 1971 Wet Clutch w/single spring 1972 1000cc engine replaces 883cc engine 1972-75 Bendix Carb 1972-76 Late-style barrel oil pump 1973 1st AMF production Harley models 1973 35mm Kayaba forks & single-disk front brake 1975 35mm Showa forks 1976-87 Keihin butterfly carb (not CV) 1977 Gerotor oil pump 1978 late-79 Electronic & Mechanical Ignition 1979 Last year for XLCH 1979-81 2nd Generation Frame 1980 Electric Start Only

Sources

Harley-Davidson Motor Company
3700 W. Juneau Ave.
Milwaukee, WI 53208
414-342-4680
www.harley-davidson.com

Buddy Stubbs Arizona Harley-Davidson
Motorcycle Museum
13850 N Cave Creek Rd
Phoenix, AZ 85022
602-971-3400
www.buddystubbs.com

Motorcycle Hall of Fame Museum
13515 Yarmouth Dr.
Pickerington, Ohio 43147
614-856-2222
www.motorcyclemuseum.org