Flathead motorcycles are a type of bike that was a standard for pre-war motorcycles, in particular US V-twins such as Harley-Davidson and Indian, some British singles, BMW flat twins and Russian copies thereof. [1]
Flathead motorcycles have side-valves contained within the engine block, instead of in the cylinder head, as in an overhead valve engine. This early engine design has mostly fallen into disuse. [2] [3]
In 1925 Cleveland Motorcycle Manufacturing Company released a motorcycle with a 36.5 cubic inches (598 cc) T-head four-cylinder engine designed by L. E. Fowler. [4] [5]
The flathead engine saw service in Harley-Davidson motorcycles beginning with the Model WS flat-twin, produced from 1919 to 1923, [6] and continuing in 1924 with single-cylinder export-model 21-cubic-inch (340 cc) and 30.5-cubic-inch (500 cc) singles and continued in Servi-Cars until 1973. In the domestic U.S. market, the 45-cubic-inch (740 cc) (primary VIN letter) D model (1929 to 1931) and its technical descendant, the (primary VIN letter) R model (1932 to 1936), started Harley's side-valve tradition in the 45-cubic-inch displacement class. The D and R models featured a total-loss oiling system and were succeeded in 1937 by the (primary VIN letter) W 45, which had recirculating oil lubrication. The WLA (W = return oil, L = performance, A = army) went on to serve in World War II as the U.S. and Canadian Army's WLC (C = Canada) primary two-wheeled mount and subsequently as a civilian middleweight through 1952. The engine continued virtually unchanged with 2.745" bore and 3.8125" stroke with various G-based designations in the three-wheeled Servi-Car until production ceased in 1973.
In 1952, the K series flatheads was introduced with the same bore and stroke, selling in parallel with the W series (which was discontinued after 1952), designed to compete with British sporting motorcycles of the time. The K models featured a 750cc unit construction engine and transmission case, right side foot shift and left side foot brake. From 1954 to 1956, the KH received an increase in stroke to 4-9/16" to bring displacement to 888cc (54 cubic inches). [7] The K series was replaced by the overhead valve Sportster series in the retail market in 1957. [8]
The American Motorcycle Association (AMA) class C rules of 1952 allowed sidevalves of 750cc to compete against 500cc overhead valve bikes. The 750cc KR factory racer was highly competitive in dirt track and road racing, and was produced in limited numbers until 1969, [9] when the AMA changed the rules by increasing the Class C displacement limit to 750 cc. Without the displacement advantage, the KR flatheads were not competitive against 750 cc overhead valve bikes. [10]
In 1930, the 74-cubic-inch (1,210 cc) VL flathead replaced the JD Big Twin, which had featured intake-over-exhaust (IoE) valve configuration. The VL had a single downtube frame and total loss oiling, culminating in an 80-cubic-inch (1,300 cc) version (VLH) in 1935. In 1937, that engine was redesigned to include a recirculating lubrication system, and designated the model U, and it went into the same frame and running gear configuration as the model E Knucklehead, which had originated in 1936. The U continued to be produced in varying configurations as a 74 cubic inch U & UL (1937 to 1948), and 80 cubic inch UH & ULH engine (1937 to 1941). By 1948, the first year of the aluminum-head Panhead, it had been thoroughly superseded and outsold in the marketplace by the superior performance of the overhead valve model Big Twins.
Harley-Davidson, Inc. is an American motorcycle manufacturer headquartered in Milwaukee, Wisconsin, United States. Founded in 1903, it is one of two major American motorcycle manufacturers to survive the Great Depression along with its historical rival, Indian Motorcycles. The company has survived numerous ownership arrangements, subsidiary arrangements, periods of poor economic health and product quality, and intense global competition to become one of the world's largest motorcycle manufacturers and an iconic brand widely known for its loyal following. There are owner clubs and events worldwide, as well as a company-sponsored, brand-focused museum.
The Honda CB750 is an air-cooled, transverse, in-line-four-cylinder-engine motorcycle made by Honda over several generations for year models 1969–2008 with an upright, or standard, riding posture. It is often called the original Universal Japanese Motorcycle (UJM) and also is regarded as the first motorcycle to be called a "superbike".
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A motorcycle engine is an engine that powers a motorcycle. Motorcycle engines are typically two-stroke or four-stroke internal combustion engines, but other engine types, such as Wankels and electric motors, have been used.
The Harley-Davidson Sportster is a line of motorcycles produced continuously since 1957 by Harley-Davidson. Sportster models are designated in Harley-Davidson's product code by beginning with "XL". In 1952, the predecessors to the Sportster, the Model K Sport and Sport Solo motorcycles, were introduced. These models K, KK, KH, and KHK of 1952 to 1956 had a sidevalve engine, whereas the later XL Sportster models use an overhead valve engine. The first Sportster in 1957 had many of the same features of the KH including the frame, fenders, large gas tank and front suspension.
The intake/inlet over exhaust, or "IOE" engine, known in the US as F-head, is a four-stroke internal combustion engine whose valvetrain comprises OHV inlet valves within the cylinder head and exhaust side-valves within the engine block.
Unit construction is the design of larger motorcycles where the engine and gearbox components share a single casing. This sometimes includes the design of automobile engines and was often loosely applied to motorcycles with rather different internal layouts such as the flat twin BMW models.
The Evolution engine is an air-cooled, 45-degree, V-twin engine manufactured from 1984 by Harley-Davidson for the company's motorcycles. It was made in the 1,340 cc (82 cu in) displacement for Harley-Davidson Big V-twins bikes, replacing the Shovelhead engine until 2000 when the last EVO was placed in a production factory custom FXR4. In 1999, it was replaced by the Harley-Davidson Twin Cam 88 in the Touring and Dyna model and in 2000 in the Softail models. Also available in the Sportster model beginning in 1986, it was made in the 1,100 cc (67 cu in) displacement until 1988 and is still made in the 883 cc (53.9 cu in) and 1,200 cc (73 cu in) displacements for the Harley-Davidson Sportster, replacing the ironhead Sportster engine.
The Harley-Davidson WLA is a Harley-Davidson motorcycle that was produced to US Army specifications in the years during and around World War II. It was based on an existing civilian model, the WL, and is of the 45 solo type, so called due to its 45-cubic-inch (740 cm3) engine displacement and single-rider design. It acquired the nickname "Liberator".
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Harley-Davidson FL is a model designation used for Harley-Davidson motorcycles since 1941, when F referred to the new large capacity 74 cui (1200cc) variant of the V-2 Overhead valve engine (″Knucklehead″) that was introduced in 1936 as Model E with 61 cui (1000cc). The presence of an additional letter L indicated higher compression, offering more power but requiring higher octane gasoline. In 1950s, the low compression version was discontinued, and in 1952 also the low capacity EL, making FL the standard engine and model designation for decades to come.
The Harley-Davidson XA was a flat-twin, shaft drive motorcycle made by Harley-Davidson for the US Army during World War II.
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The Harley-Davidson XR-750 is a racing motorcycle made by Harley-Davidson since 1970, primarily for dirt track racing, but also for road racing in the XRTT variant. The XR-750 was designed in response to a 1969 change in AMA Grand National Championship rules that leveled the playing field for makes other than Harley-Davidson, allowing Japanese and British motorcycles to outperform the previously dominant Harley-Davidson KR race bike. The XR-750 went on to win the most races in the history of American Motorcyclist Association (AMA) racing.
American Flat Track is an American motorcycle racing series. The racing series, founded and sanctioned by the American Motorcyclist Association (AMA) in 1954, originally encompassed five distinct forms of competitions including mile dirt track races, half-mile, short-track, TT steeplechase and road races. The championship was the premier motorcycle racing series in the United States from the 1950s up until the late 1970s.
The Cleveland Motorcycle Manufacturing Company, sometimes called Cleveland Motorcycle, was a motorcycle manufacturer in Cleveland, Ohio, from 1902 to 1905 and again from 1915 to 1929.
The Harley-Davidson Model W, also known as the Sport Twin, is a motorcycle made by Harley-Davidson from 1919 to 1923. Unusually for a Harley-Davidson motorcycle, the Model W had a flat-twin engine and a trailing link fork. The Model W set speed records on runs from New York City to Chicago and from the Canada–United States border to the Mexico–United States border. Slow home market sales led to the end of production after four years.
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The Harley-Davidson KR or KR750 was a 45.125 cu in (739.47 cc) displacement V-twin engine racing motorcycle made by Harley-Davidson from 1953 through 1969 for flat track racing. It was also used in road racing in the KRTT faired version. When the KR was first introduced, it dominated motorcycle racing in the United States. In 1970 it was replaced by the long-lived and US race-winning Harley-Davidson XR-750.
The Sport Model engine was Harley's first side-valve.[ permanent dead link ]