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53-595: In 1919, BMW designed and manufactured the flat-twin M2B15 engine for Victoria Werke AG of Nuremberg. The engine was initially intended as a portable industrial engine, but found its main use in Victoria motorcycles. The engine was also used in the Helios motorcycle built by Bayerische Flugzeugwerke, which was later merged into BMW AG. Bayerische Flugzeugwerke also manufactured a small two-stroke engined motorcycle, called

106-481: A rocking couple is present, since each cylinder is slightly offset from the other member of its pair due to the distance between the crankpins along the crankshaft. An alternative configuration for flat engines is as a 180-degree V engine , which has been used on most twelve-cylinder flat engines. In this configuration, each pair of pistons shares a crankpin , this being simpler than the boxer configuration, where each piston has its own separate crankpin. In 1902,

159-430: A boxer-twin engine do however generate a rocking couple , due to the offset distance between the pistons along the crankshaft. A commonly used ignition system is wasted spark , which is a simple ignition system using a double-ended coil firing both spark plugs on each revolution (i.e. during both the compression and exhaust strokes). This system is distributorless and requires only a single contact breaker and coil for

212-526: A diesel version of its existing 688 cc petrol flat-twin in 1932, and went on to produce flat-twin diesel and petrol engines for a variety of industrial and marine uses into the 1950s. Two-stroke flat-twins were often used as outboard motors for boats, as they were smoother than single-cylinder engines. In the 1940s, they were largely replaced by straight-twin two-stroke engines, which were easier to start and no longer had excessive amounts of vibration. Flat engine#Boxer engine A flat engine

265-639: A hobbyist inventor. This engine used the unusual design of a single shared crank pin and double acting pistons. In 1908, the French company Dutheil-Chalmers began production of flat-twin aircraft engines, which used two counter-rotating crankshafts. The Dutheil-Chlamers engine was used by the 1907 Santos-Dumont Demoiselle No. 20 experimental airplane, with later versions of this airplane being produced with flat-twin engines from Darracq and Clément-Bayard . Most piston-engined aircraft used more than two cylinders, however other flat-twin aircraft engines from

318-499: A low centre of mass , low vibration, suitability for shaft drive, and equal cooling of the cylinders (for air-cooled engines). The most common design of flat engine for motorcycles is the boxer-twin, beginning with the 1905 Fée flat-twin engine, manufactured by the Light Motors Company, which was the first production motorcycle engine. BMW Motorrad have a long history of boxer-twin motorcycles, beginning in 1923 with

371-407: A partial vacuum inside the crankcase, in order to reduce oil leaks when an oil seal malfunctions. This was achieved by using a one-way valve (a leather or rubber flap over a hole in the crankcase), to let air escape the crankcase but not enter it. The beginnings of the flat-twin engine were in 1896, when Karl Benz obtained a patent for the design. A year later, his company Benz & Cie unveiled

424-608: A pulley on the rear wheel via a chain. Manufacture of the Fairy was taken over by the Douglas Engineering Company , one of Light Motors' suppliers, when the Light Motors Company folded in 1907. Later in 1907, Douglas changed the drivetrain from the chain and pulley design to a belt-drive system driven directly from the engine. Later developments of the Douglas motorcycle were made with the cylinders in line with

477-490: A rarity and V engines have almost vanished except in historical aircraft. They have even replaced radial engines in many smaller installations. The advantages of flat engines are a short length, low centre of mass and suitability for air cooling (due to the well-exposed, large-surface-area cylinders and cylinder heads, and their short length). Compared with the more common straight engines , flat engines have better primary balance (resulting in less vibration); however,

530-495: A rear-domed piston, crankcase mixers and refined ignition system . Most flat-twin engines use a boxer configuration for the crankshaft and are therefore called "boxer-twin" engines. In a boxer-twin engine, the 180° crankshaft moves the pistons in phase with each other, therefore the forces generated by one piston are cancelled out by the other, resulting in excellent primary balance. The evenly spaced firing order also assists in reducing vibration. The equal and opposite forces in

583-510: A single-cylinder or V-twin engine, however this arrangement would result in an excessively long wheelbase for flat-twin engines. Solutions to this problem included using a countershaft below the engine (as used by the Douglas Fairy), or a gearbox located above the engine, although in some cases the cylinders were short enough to use the gearbox in the traditional location behind the engine. In 1916, most flat-twin motorcycles still used

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636-436: A trailing link design suspended by a leaf spring, similar to the forks used by Indian at the time. The rear wheel was rigidly mounted. In the original First Series, braking was accomplished solely with a "dummy rim" on the rear wheel with two padded brake shoes set within it. One would be operated by the, now traditional, right hand lever and the other by use of a heel actuated lever on the right side. Later years would reroute

689-890: A transversely-mounted engine. The European models at this time included the Bradbury 3.5 hp (2.6 kW), the Brough HB , the Douglas 2.75 hp (2.05 kW) and 4 hp (3.0 kW) models, the Humber 3.5 hp and 6 hp (4.5 kW) models, the Matchless 6 hp, the Montgomery 6 hp, Williamson Flat Twin 8 hp (6.0 kW), and the Bayerische Flugzeugwerke Helios (the predecessor to BMW's first motorcycle). Models produced in

742-405: Is a piston engine where the cylinders are located on either side of a central crankshaft . Flat engines are also known as horizontally opposed engines , however this is distinct from the less common opposed-piston engine design, whereby each cylinder has two pistons sharing a central combustion chamber. The most common configuration of flat engines is the boxer engine configuration, in which

795-478: Is a two-cylinder internal combustion engine with the cylinders on opposite sides of the crankshaft. The most common type of flat-twin engine is the boxer-twin engine , where both pistons move inwards and outwards at the same time. The flat-twin design was patented by Karl Benz in 1896 and the first production flat-twin engine was used in the Lanchester 8 hp Phaeton car released in 1900. The flat-twin engine

848-539: The BMW R32 Several motorcycles have been produced with flat-four engines, such as the 1938–1939 Zündapp K800 and the 1974–1987 Honda Gold Wing . In 1987, the Honda Gold Wing engine was upsized to a flat-six design. When used in cars, advantages of flat engines are a low centre of mass (which improves the handling of the car), short length, low vibration and suitability for air cooling (due to

901-982: The Riedel firm in Germany designed and manufactured a two-stroke flat-twin engine as jet engine starter motors for the Junkers Jumo 004, BMW 003 and Heinkel HeS 011 jet engines The Maytag 'Model 72' flat-twin engines— produced from 1937 until some time between 1952 and 1960— were used in various applications including clothes washing machines. Electrical generators using flat-twin engines were built by Norman Engineering Company from 1932 to 1968 and by Douglas during World War II. Enfield Industrial Engines (part of Royal Enfield ) produced flat-twin two-stroke petrol engines during World War II which were used for generators and other military uses. After 1945, Enfield produced flat-twin diesel engines, with applications including farm and marine use. Coventry Victor introduced

954-487: The Subaru EE engine became the world's first passenger car diesel boxer engine. This engine is a turbocharged boxer-four with common rail fuel injection. Ferrari used flat-twelve engines for various Formula One cars in the 1970s. A road car flat-twelve engine (using a 180-degree V12 configuration) was used for the 1973-1984 Ferrari Berlinetta Boxer , 1984-1996 Ferrari Testarossa and their derivatives. Toyota uses

1007-601: The Subaru Leone (1971–1994), Subaru Legacy (1989-present) and Subaru Impreza (1992–present). The front half-shafts come out of a front differential that is part of the gearbox. A rear driveshaft connects the gearbox to the rear half-shafts. The traditional front-engine, rear-wheel-drive layout is relatively uncommon for cars with flat engines, however some examples include the Toyota 86 / Subaru BRZ (2012–present), Jowett Javelin (1947–1953), Glas Isar (1958–1965) and

1060-486: The Tatra 11 (1923–1927). The first flat engine was produced in 1897 by German engineer Karl Benz . Called the kontra engine, it was a boxer-twin design. Early uses of flat engines in cars include the 1900 Lanchester 8 hp Phaeton boxer-twin, the 1901 Wilson-Pilcher boxer-four, the 1904 Wilson-Pilcher 18/24 HP boxer-six and the 1903 Ford Model A , the 1904 Ford Model C and the 1905 Ford Model F . In 1938,

1113-689: The Volkswagen Beetle (then called the "KdF-Wagen") was released with a rear-mounted flat-four engine. This Volkswagen air-cooled engine was produced for many years and also used in the Volkswagen Type 2 (Transporter, Kombi or Microbus), the Volkswagen Karmann Ghia sports car and the Volkswagen Type 3 compact car. A water-cooled version, known as the Wasserboxer , was introduced in 1982 and eventually replaced

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1166-650: The 1920s and 1930s include the American Aeronca E-107 and Aeronca E-113 , the British Bristol Cherub , and the Czechoslovakian Praga B2 . The HKS 700E is an oil-cooled flat twin for ultralight aircraft that is currently in production. In larger aircraft, flat-twin engines have been used in auxiliary power units (APUs). A notable example was made by ABC Motors in the 1920s and 1930s. During World War II,

1219-528: The 1930s and 1940s. During World War II, a boxer-twin engine called the "Riedel starter" was used as a starter motor/mechanical APU for the early German jet engines, such as the Junkers Jumo 004 and BMW 003 . Designed by Norbert Riedel , these engines have a very oversquare stroke ratio of 2:1 so that they could fit within the intake diverter, directly forward of the turbine compressor. Flat engines offer several advantages for motorcycles including

1272-536: The 1957-1975 Puch 500 , the 1957-1959 BMW 600 and the 1959-1965 BMW 700 . The Brazilian manufacturer Gurgel Motores used an in-house developed water-cooled boxer-twin engine (Enertron engine) and the Volkswagen air-cooled boxer-four in several models from 1988 to 1994. The Toyota U engine was an air-cooled flat-twin engine produced from 1961 to 1976. Introduced in the Toyota Publica subcompact car,

1325-528: The 1960s. The Australian lawnmower manufacturer Victa also produced a flat-twin engine push mower from August 1975 to 1980 dubbed the ‘Twin 500’, and later the ‘Supreme’. These engines were manufactured in Canada. They are very sought after as only small numbers were produced, most likely due to ignition- and fuel-related problems in early models. In the Supreme (the later model) all these problems were fixed with

1378-479: The Flink, which was not successful. After the merger, General Director of BMW Franz Josef Popp asked Design Director Max Friz to assess the Helios motorcycle. Upon completing his assessment, Friz suggested to Popp that the best thing that could be done with the Helios would be to dump it in the nearest lake. More specifically, Friz condemned the Douglas -style transverse-crankshaft layout, which heavily restricted

1431-502: The Pearse monoplane (which would later become one of the first aircraft to achieve flight) was powered by a flat-twin engine. Amongst the first commercially-produced aircraft to use a flat engine was the 1909 Santos-Dumont Demoiselle range of aeroplanes, which was powered by boxer-twin engines. Several boxer-four engines have been produced specifically for light aircraft. A number of manufacturers produced boxer-six aircraft engines during

1484-470: The R32 to a top speed of 95 km/h (59 mph). The engine and gear box formed a single unit . The new engine featured a recirculating wet sump oiling system at a time when most motorcycle manufacturers used a total-loss oiling system . BMW used this type of recirculating oiling system until 1969. To counter the cooling problems encountered with the Helios, Friz oriented the R32's M2B33 boxer engine with

1537-534: The U engine was also used in the Toyota MiniAce small commercial vehicle and the Toyota Sports 800 sports car. The benefits of using a flat-twin engine mounted with the crankshaft running perpendicular to the frame (therefore the cylinders being in line with the frame) are a low centre of gravity and that a belt-drive or chain-drive system can be used to transmit drive to the rear wheel. However,

1590-600: The United States included the Indian Model O and the Harley-Davidson Model W . The main benefit of mounting a flat-twin engine with the crankshaft in line with the frame (therefore the cylinders sitting sideways in the frame) is that an air-cooled engine receives the same amount of cooling for each cylinder. The Harley-Davidson XA , which used a flat-twin engine with the cylinders across

1643-446: The air-cooled versions. The majority of sports cars throughout Porsche's history are powered by flat engines, beginning with its first car; the 1948-1965 Porsche 356 used an air-cooled boxer-four engine. Also using boxer-four engines were the 1969-1976 Porsche 914 , the 1965-1969 Porsche 912 and the 2016-present Porsche Boxster/Cayman (982) . The Porsche 911 has exclusively used boxer-six engines from its introduction in 1964 until

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1696-555: The cooling of the rear cylinder. Popp and Friz then agreed to a near-term solution of redesigning the Helios to make it more saleable and a long-term solution of an all new motorcycle design. This new design was designated the BMW R32 and began production in 1923, becoming the first motorcycle to be badged as a BMW. The M2B33 engine in the R32 had a displacement of 494 cc and had a cast-iron sidevalve cylinder/head unit. The engine produced 8.5 hp (6.3 kW), which propelled

1749-454: The cylinder heads projecting out on each side for cooling, as used in the earlier British-manufactured ABC . Unlike the ABC, however, the R32 used shaft final drive from a flexible coupling on the gearbox output shaft to a pinion driving a ring gear on the rear wheel hub. The R32 had a tubular steel frame with twin downtubes that continued under the engine to the rear wheel. The front fork had

1802-472: The disadvantages are increased width and the need to have two cylinder heads. Compared with V engines – the most common layout for engines with six cylinders or more – flat engines again have a lower centre of mass, and, for six-cylinders, better primary balance; the disadvantage is again their being wider. The most common usages of flat engines are: Most flat engines use a "boxer" configuration, where each pair of opposing pistons move inwards and outwards at

1855-555: The downsides are uneven heat distribution (the front cylinder is more heavily cooled than the rear cylinder) and a longer wheelbase is often required due to the length of the engine. The first flat-twin motorcycle engine was built in 1905 by the Light Motors Company in the United Kingdom. Originally named the Fée (renamed "Fairy" soon after its introduction), it was designed as a "bicycle engine system" which transmitted power to

1908-486: The engine. The boxer-twin configuration can cause pressuring of the crankcase during each inward piston stroke and de-pressurisation during each outward piston stroke, since both pistons are moving inwards or outwards at the same time. This crankcase pumping effect (also found on single-cylinder engines and 360° parallel-twin engines) is usually addressed by means of a crankcase breather. The Citroën 2CV boxer-twin engine took advantage of this pumping effect to maintain

1961-500: The first flat-twin engine, a boxer design called the "contra engine". In 1900, The Lanchester Engine Company began production of the Lanchester 8 hp Phaeton , which used a flat-twin engine. This engine had an unusual design of two counter-rotating crankshafts, with each piston attached to its crankshaft by a thick connecting rod. Each piston was also connected to the other crankshaft by two thinner connecting rods, causing

2014-482: The first uses of a turbocharger in a mass-produced automobile. The Subaru EA engine was introduced in 1966 and began Subaru 's line of boxer-four engines that remain in production to this day. Most of Subaru's models are powered by a boxer-four engine in either naturally aspirated or turbocharged form. A print ad for the 1973 Subaru GL coupe referred to the engine as "quadrozontal". The company also produced boxer-six engines from 1988 to 1996 and 2001–2019. In 2008,

2067-563: The frame until the Second World War. Other early flat-twin motorcycles used a similar layout, with their cylinders aligned along the frame and therefore with the crankshaft running transverse to the frame. In 1914 the main supplier of rear-hub gearboxes, Sturmey-Archer , introduced a 3-speed countershaft gearbox with integral kick-starter, which posed a design problem for motorcycles with transversely-mounted flat-twin engines. This gearbox could be relatively easily located behind

2120-422: The frame, maintained an oil temperature 100 °F (56 °C) cooler than a Harley-Davidson WLA with a V-twin with the cylinders in line with the frame. A side benefit is that the cylinders provide protection to the rider in the event of a collision or fall, and keeps their feet warm in cold weather. The downsides are that the engine cannot be mounted as close to the ground (otherwise the cylinders can scrape

2173-462: The front right lever and cable to a front drum brake. The R32 established the boxer-twin, shaft-drive powertrain layout that BMW would use until the present. BMW used shaft drives in all of its motorcycles until the introduction of the F650 in 1994 and continues to use it on their boxer-twin motorcycles. Ref: Any picture of the bike shows the trailing links. Flat-twin A flat-twin engine

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2226-468: The ground during cornering) and that it exposes the cylinders and valve covers to the danger of collision damage. Longitudinal mounting also means that the torque reaction will twist the motorcycle to one side (such as on sharp acceleration/deceleration or when opening the throttle in neutral) instead of shifting the weight balance between the front and rear wheels. However, many modern motorcycles reduce this effect by rotating flywheels or alternators in

2279-462: The opposite direction to that of the crankshaft. One of the first motorcycles with a longitudinally-mounted flat-twin engine was the 1916 ABC , which was built in the United Kingdom. To accommodate chain drive, the ABC used a bevel drive at the gearbox to change the direction of the drive through ninety degrees. BMW's first motorcycle, the 1923 BMW R 32 was another early example of a longitudinally-mounted flat-twin engine, although it this case

2332-711: The pistons of each opposed pair of cylinders move inwards and outwards at the same time. The other configuration is effectively a V engine with a 180-degree angle between the cylinder banks: in this configuration each pair of cylinders shares a single crankpin, so that as one piston moves inward, the other moves outward. The first flat engine (Benz Contramotor) was built in 1897 by Karl Benz . Flat engines have been used in aviation, motorcycle and automobile applications. They are now less common in cars than straight engines (for engines with fewer than six cylinders) and V engines (for engines with six or more cylinders). Flat engines are more common in aircraft, where straight engines are

2385-457: The power was transmitted to the rear wheel via a shaft drive. Over time, longitudinal mounting became more common for flat-twin engines. BMW has a long history of flat-twin engine motorcycles, as do Ural (Russia) and Dnepr (Ukraine). In 1902, the Pearse monoplane (which would later become one of the first aircraft to achieve flight) was powered by a flat-twin engine built on a farm by

2438-615: The present. In 1997, the Porsche 911 switched from being air-cooled to water-cooled. Porsche flat-eight engines were used in various racing cars throughout the 1960s, such as the 1962 Porsche 804 Formula One car and the 1968-1971 Porsche 908 sports car. A flat-twelve engine was also produced by Porsche for the 1969-1973 Porsche 917 sports car. Chevrolet used a horizontally opposed air-cooled 6 cylinder engine in its Corvair line during its entire production run from 1960 to 1969 in various applications and power ratings, including one of

2491-415: The same time, somewhat like boxing competitors punching their gloves together before a fight. Boxer engines have low vibration, being they are the only common configuration that has no unbalanced forces, regardless of the number of pairs of cylinders. Boxer engines therefore do not require either a balance shaft or counterweights on the crankshaft to balance the weight of the reciprocating parts. However,

2544-605: The short length of flat engines, locating a flat engine outside of the car's wheelbase results in minimal overhang. Therefore, many cars with flat engines have used a rear-engine, rear-wheel-drive layout . Examples include the flat-twin BMW 600 (1957–1959) and BMW 700 (1959–1965); the flat-four Tatra 97 (1936–1939), Volkswagen Beetle (1938–2003) and Porsche 356 (1948–1965); and the flat-six Chevrolet Corvair (1959–1969), Porsche 911 (1963-present), and Tucker 48 (1947–1948). The opposite layout, front-engine front-wheel drive ,

2597-461: The two pistons to move on the same axis. It also had the torque reaction of one crankshaft cancel the torque reaction of the other, cancelling torque reaction in the engine. Lanchester used this engine design until 1904. Other early uses of flat-twin engines were 1903-04 Ford Model A , the 1904-1905 Ford Model C , the 1905-1906 Ford Model F . and several Jowett Cars models from 1910 to 1937. The Citroën 2CV , produced from 1948 to 1990,

2650-478: The well exposed, large surface area, cylinder heads and short length). However the larger width of flat engines (compared with the more common inline and V layouts) is a drawback, particularly when the engine is located between the steered wheels. Flat engines were used by various automobile manufacturers – mostly with a boxer-four design – up until the late 1990s. Since then, only Porsche and Subaru have remained as significant manufacturers of flat engines. Due to

2703-457: Was also common for cars with flat engines. Examples include the Citroën 2CV (1948–1990), Panhard Dyna X (1948–1954), Lancia Flavia (1961–1970), Citroën GS (1970–1986), Alfa Romeo Alfasud (1971–1989) and Subaru Leone (1971–1994). Subaru have been producing cars with a front-engine, four-wheel-drive layout powered by flat engines (mostly boxer-four engines) since 1971. Examples include

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2756-680: Was one of the first front-wheel drive cars to use a flat engine. The 2CV was powered by an air-cooled boxer-twin engine. Also in 1948, the Panhard Dyna X was released with front-wheel drive and an air-cooled boxer-twin engine. Other cars following World War II using boxer-twin engines were the 1945-1954 Jowett Bradford van, , the 1961-1976 DAF Daffodil , the 1961-1978 Toyota Publica , the 1965-1969 Toyota Sports 800 sportscar and several front-wheel drive models from Citroën and Panhard . Several rear-engined cars were also produced with boxer-twin engines originally designed for motorcycles, such as

2809-402: Was used in several other cars since, however a more common usage is in motorcycles; early models oriented the cylinders in line with the frame, however later models switched to the cylinders being perpendicular to the frame to provide even cooling across both cylinders. Flat-twin engines were also used in several aircraft up until the 1930s and in various stationary applications from the 1930s to

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