The Original Harley-Davidson Sportster XL : Adding the Sport

A year before Triumph introduced the Bonneville, Harley-Davidson had a hot rod of its own: the 55-cubic inch Sportster XL “CH” variant.

Introduced in 1957 as the model Harley-Davidson Sportster XL was a direct development from the 45-cubic-inch flathead model K and the 55-cu. in. KH/KHK. The iron cylinders used a new three-inch (76.2mm) bore with the 3-9/16-inch (96.85mm) 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 overhead 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 (distributor).

A single Linkert carburetor fed the engine, which drove through a chain primary to a multi-plate clutch and four-speed “trapdoor” gearbox (allowing the gear train to be removed without splitting the cases). Final drive was by chain on the right side. The foot shifter was also on the right with the one up, three down pattern seen on most British bikes at the time. The twin downtube chassis connected to 18-inch wheels by a telescopic front fork and dual coil spring/damper units attached to the seat subframe. Eight-inch drum brakes provided stopping power.

The XL produced an estimated 40 hp, and turned in a 15-second quarter with a top speed of 101 mph while the 42-hp, 1957 Triumph Tiger 110 returned 16 seconds and similar top speed. So did H-D intend to race their new bike? AMA’s production-based Class C allowed OHV bikes of 500ccc to compete against side-valve machines up to 750cc—or 45 cubic inches. So the side-valve 750cc K was eligible for AMA class C racing, but the new OHV 883cc XL was not.

In launching the XL range, the Motor Company acknowledged two things: overhead valves were the way forward; and the Sportster was not going racing in Class C anytime soon. So the side-valve 750cc KRTT would soldier on until Class C rules were changed for 1969, prompting the development of the Sportster-based XR750.

With its deeply-valanced fenders, generous 4.4-gallon fuel tank, large headlight and subdued exhaust, most reviewers assumed the XL was intended just for touring. But while the Sportster’s 883cc capacity was too big for Class C, it was fine for open class TT racing. This was nothing like the Isle of Man version of the TT, but more of a cross-country steeplechase. In the late 1950s, Triumph Trophy-birds, BSA Catalina Scramblers and Matchless’s G80s were very competitive, challenging the KRTTs. This led to the development of the XLR.

With higher compression (around 9:1) and larger valves, the XLR also used a trick frame with higher quality steel, meaning thinner walls and lighter weight. It also sported the now famous “peanut” gas tank borrowed from the S range. Ignition was by magneto. And as the increased power could be produced reliably, it made sense to produce a “customer” version. This became the 1958 XLH.

The XLH was essentially a XL with the XLR’s cylinder heads, though the castings were slightly different—long reach sparkplugs for the R, short reach for the H. Everything else was as the XL, though turn signals were also added to the 1958 specification.

The 1958 XLCH was a far more radical departure. The “CH” designation, quite logical in Harley-speak (C for stripped bodywork, H for high performance), was variously interpreted as “Competition Hot” or “California Hotrod.” Though not an XLR, it could almost have passed for one. The stock XLH was stripped of its lights, mufflers and other extraneous items (though lights and a licence plate bracket were available for an extra $60), the fenders were bobbed and the peanut tank fitted. The idea seemed plain: here was an over-the-counter hotrod that you could ride to the desert or track, compete in a TT race, and ride home again—as long as you did it in daylight!

Superficially, the main differences were the XLR’s missing front fender and alloy wheel rims. H-D also listed a version called the XLC with stripped bodywork and the base XL motor, but few, if any, were sold.

In fact, Sportsters weren’t big sellers in 1958 at all. Of 12,676 Harley-Davidsons sold that year, just 1,529 were XL variants. The Sportster range was outsold four times by the Big Twin FL range and almost three times by the humble 165cc two-stroke S range. According to the Harley-Davidson Museum, just 579 XLs, 711 XLHs and 239 XLCHs ended up in buyers’ hands in 1958.

The XLCH reappeared in the catalogue for 1959, but in a completely different guise. Mufflers and lights were back, though the performance modifications and magneto were retained. The ‘59 also sported a new smaller headlight with the Classic “eyebrow” cowling and a high-level exhaust. And it proved to be the most popular Sportster model with 1,059 sold, compared with 947 XLHs (coil ignition and low exhaust but with the high compression engine) and just 42 base-model Sportster XL bikes.

Performance numbers quoted at the time are inconsistent, but it seems likely a good 1959 XLCH was making around 50 hp at the crank and weighed around 490 pounds (222 kg) wet, compared with 46 hp and maybe 430-440 pounds for the contemporary Triumph Bonneville T120. As such the XLCH would turn 14-second quarters at over 90-95 mph: the Bonnie’s performance was similar.

The 1959 XLCH seemed to be the “right stuff,” and set the pattern for iron-engine Sportsters for the next decade. The next major innovation: electric start. But that would have to wait until 1967.

by Robert Smith Canadian Biker Issue #313

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The Original Harley-Davidson Sportster XL : Adding the Sport

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