The 'Harley-Davidson' motorcycle company's humble beginnings can be traced back to a small wood barn in Milwaukee, Wisconsin, back in 1903. After designing a small gas engine for mounting on a bicycle frame, William S. Harley (1880—1943) joined with Arthur Davidson (1881—1950) to build their first motorcycle, the "Silent Grey Fellow."
In 1906, a new factory was built on Chestnut Street, which would later be renamed Juneau Avenue. The company incorporated on September 17th, 1907, and the founding partners were soon joined by Arthur's brothers Walter Davidson and William A. Davidson. The Silent Grey Fellow was an overnight sucess, and by the 1910s the original 1903 prototype for the Silent Grey Fellow was being used as a promotional mascot, having clocked over 100,000 miles (1909 Model 5A ' Silent Grey Fellow' shown above).
Zoom: 1917 Harley-Davidson Model T (background: 1912 Harley Model X-8)
In 1908, Walter Davidson scored a perfect 1,000 points at the 7th Annual FAM (Federation of American Motorcyclists) "endurance and reliability" contest, as well as winning FAM's "economy record" (188.234 mpg) three days later. From here, Harley-Davidson's reputation for reliability grew, and HD began selling police duty motorcycles to the Detroit Police Department.
The Harley Davidson 'V-Twins'
In 1909, Harley Davidson introduced its first v-twin powered motorcycle, powered by a 7 hp, 49.5 cubic inch motor. The first twins used atmospheric-type intake valves that were inherited from the single cylinder engine design. The 09 twins were discontinued the same year, reappearing in 1911 with redesigned IOE (inlet-over-exhaust) intake valves (nicknamed "pocket valves") which were mechanically operated. These Pocket Valve twins were produced in 61ci and 74ci displacements.
Zoom: 1923 Harley-Davidson JDCA Board Track Racer
The company introduced its Model W Sport-Twin in 1919. The Model W was powered by a horizontally opposed side-valve, twin cylinder engine. The engine and transmission were mounted in the same cases making this model the first Harley Davidson Twin with 'unit' engine construction.
Harley sales began to slow during the early 1920s recession, and a Harley Davidson motorcycle was now more expensive than Ford's least-expensive automobile. In reaction to this, HD introduced small-displacement single-cylinder motorcycles that could compete with the European bikes. This decision was not well received by the public, and Harley Davidson abandoned the marketing strategy in the mid 20s.
1929 Harley-Davidson Model JDH
In the late 1920s, Harley Davidson introduced the Model JH and JDH, advertising the JDH as the "fastest model ever," with a top speed of 85 to 100 mph. The Model JH had a 1000 cc (61 cubic-inch) engine, and the JDH had a 1200 cc (74 cubic-inch) version. The twin-cam engine had a 'peanut-shaped' timing gear cover which made the engine recognizable.
Harley Davidson Nomenclature
Nicknames were given for the physical characteristics of the engine, that readily identified the era in which a particular Harley was built, and its engine/cylinder-head design.
Harley-Davidson 'Flathead' Side Valve (1930 to 1956)
Harley Davidson's "Flathead," or "Side Valve" engine design dates back to the early 1920s. The name comes from the location of the upside-down valves that are located alongside the cylinder, with the valve ports entering a flat combustion chamber above the cylinder bore.
1936 Harley-Davidson Model R Flathead
The 1200cc 74ci Flathead Model V (aka "Seventy-Four") replaced the long-running F-Head in 1930. The Flathead design remained popular throughout to 1940s, and the Model WLA Flathead was used by the US military during WWII, labeling it as the "bike that won the war."
1948 Harley-Davidson Model WR Flathead
Toward the end of Flathead production in the late 1940s, the design was relegated to smaller displacement V-twins like 700cc to 750cc Models WR, and WHR, or the Model K. The last of the Flathead engines was used on the 1956 Model KH, but the Flathead engine and the more advanced OHV 'Knucklehead' engine coexisted for nearly eleven years.
Harley-Davidson 'Knucklehead' (1936 to 1947)
1936 was the first year for the "Model E," which was nicknamed as the "Knucklehead" due to the knuckle shape of its engine valve covers. The Model E was a slowly gained popularity, but it was the distance record set by Fred Ham that put the knucklehead Model E into the history books.
1937 Harley-Davidson EL 1000 Knucklehead
1940 Harley-Davidson EL 1000 Knucklehead
1947 Harley-Davidson EL 1000 Knucklehead
The last of the 'Knuckleheads' was produced by Harley-Davidson in 1947. The new versions of Harley's OHV engine were introduced in 1948, featuring chrome-plated valve covers that resembled upside-down cake pans. This was the beginning of Harley-Davidson's "Panhead" era.
HD EL 61ci 1000cc V-Twin Knucklehead Engine
Harley-Davidson 'Panhead' (1948 to 1966)
The "Panhead" or "Tin Top" overhead valve engine was introduced in 1948, with a 1000 cc (61 cubic-inch), and 1200 cc (74 cubic-inch) version. 1948 also ushered in the ear of the 'telescoping front fork,' ending the long run of 'springer' fork assemblies.
Harley-Davidson Model K & KR 750 Racer (1952 to 1969)
Harley-Davidson introduced the middleweight "Model K" in 1952, along with the 'KR' series of 'competition class' road-racing or flat-track racers. The KR's "Milwaukee racing iron" engine was a 744cc side-valve flathead V-twin that produced around 30 horsepower. The K had a three-speed gearbox and limited power, but the KR with its 4-speed transmission was capable of a top speed of around 80 mph.
1959 Harley-Davidson KR Flat Tracker
Built as a replacement for Harley-Davidson's aging WR racing line, the KR would be a dominant force in dirt track and road-racing competition for almost 17 years. The KR took nearly every AMA Grand National Championship from 1954 to 1962.
1969 Harley-Davidson KRTT 750 Racer
By the late 1960s, the KRTT was capable of a 150 mph top speed, with around 50 bhp. From 1953 to 1969, the KR and KRTT delivered 13 victories at Daytona, making it one of the company's most successful road racing bikes. As the British competition started to gain an unbeatable foothold in the late 60s, HD decided to discontinue the KRTT in 1969. The final year for the street Model K was in 1956, with the 54-cubic-inch (883cc) KHK.
Harley-Davidson 'Ironhead' Sportster (1957 to 1986)
The Harley "Sportster" began in 1957 with the 54-cubic-inch OHV "Model XL," beginning one of the company's most successful and enduring model lines. Marketed as a "junior" version of the bulky Hydro-Glide line, this middleweight contender (around 480 lbs.) had an 883cc engine known as the "Ironhead," which had a larger bore and shorter stroke, producing more power than the Model KH (38 vs 40 hp). The XL also had a four-speed gearbox.
1957 Harley-Davidson XL Sportster 883
The racing KR engine was upgraded to the XLR in 1958, and the sportier XLC and XLCH street models were added as well. The 'C' in XLC stood for "compitition," while the 'H' in XLCH meant that it had a higher compression ratio of 9:1. The XLC Sportster had a small "peanut style" gas tank, narrow fenders and open straight pipes.
In 1972, the Sportster's 883cc engine was increased to 61-cubic-inches (1000cc). The Sportster line continued well beyond the Ironhead years, with its powereplant being replaced by the current Evolution, or "Evo" (aka "Blockhead") engine in 1984. The Evo engine's head and cylinders were made of aluminum instead of iron, saving weight and aiding in cooling.
Harley-Davidson 'Shovelhead' (1966 to 1984)
The Panhead engine was upgraded to the "Shovelhead" in 1966, with the main difference being the u-shaped rocker boxes which aided in head cooling. The engine's cylinder head and bottom end remained much the same. From the right side, the Shovelhead's rocker covers and cylinder heads looked similar to the early Sportster XL.
The next significant change came in 1970, with the introduction of the so-called "Cone Shovel" engine, which referred to the cone-shaped ignition cover on the engine's right side. The Shovelhead's external generator was also replaced with an alternator located inside the engine primary case.
Harley-Davidson Evo 'Evolution' (1983 to 1998)
Harley's Evo (V2 Evolution) engine made its way into the Big Twin bikes in 1983, being hailed as a major improvement to the engine's head design. The Evo engine was more reliable, burned less oil, and ran cooler than its predessors.
The Evolution was replaced with the so-called "Twinkie," or "Twin Cam 88" engine, which was the first complete engine redesign since the introduction of the OHV Knucklehead in 1936.
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The A-Z of Harley-Davidson
Harley-Davidson Racing History
1952 - 1970 Harley Davidson KRTT 750
Classic Harley Twins
100 Years of Harley Davidson
Harley-Davidson Aermacchi ERS Sprint CR/CRTT
Aermacchi Restoration & History
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