For the vehicle design where the vehicle's skin is used as a load-bearing element, see Monocoque.
1921 ABCopposed twin unit construction engine / transmission1923 BMW R32 unit construction engine / transmission
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 twinBMW models.
Prior to unit construction, the engine and gearbox had their own separate casings and were connected by a primary chain drive running in an oil bath chaincase. The new system used a similar chain drive and both had 3 separate oil reservoirs for engine, gearbox and primary drive.
Triumph and BSA were already using cast alloy chaincases and started converting to unit construction in the 1950s. A driving factor behind the BSA/Triumph change was that Lucas[1] had declared an intention to abandon production of motorcycle dynamos and magnetos, and instead produce only alternators. By contrast, Velocette, Matchless/AJS and Norton motorcycles continued to be pre-unit construction (the former machines with pressed-steel primary cases) until the end of production in the 1960s and 1970s respectively. In reality, the casings were not really "unitary", as the crankcase section was vertically divided in the middle and no oil was shared between the three portions. Only in the 1960s did Japanese motorcycles introduce the now- familiar horizontally-split clam-shell which has become almost universal.
Modern horizontally-split four stroke engines invariably use single oil reservoir (whether wet- or dry-sump; but while this simplifies matters, it is arguable that the previous system of having different types of oil for engine and gearbox is preferable. The BMC Mini was an early example of a car with the "gearbox-in-the-sump"; but this practice of using a single oil reservoir, which has become the norm for motorbikes, is generally undesirable for cars and trucks. Two stroke "total-loss" bikes always have separate oil for the gearbox, as engine oil is burned along with the fuel.
the combined unit contributes to the stiffness of the entire motorcycle.
unit construction may even enable the engine unit to become a frame stressed member.
the primary chaincase can be lighter and more compact.
the primary chaincase can be shorter, so that wheelbase may also be shorter
engine and transmission are now much more accurately aligned to each other in the frame, improving primary drive life.
the engine is cleaner and fashionably modern in appearance (compared to earlier designs).
A significant disadvantage is that there is no longer any tension adjustment possible of the chain drive between engine and transmission, and tensioning (which is almost certainly still required) must be over a rubber-faced steel slipper. However, this is quieter and the tensioner does not wear greatly. This change to unit construction meant that it was no longer possible to choose a gearbox from a different manufacturer (e.g. a close-ratio unit for racing) and to send a worn gearbox units to be rebuilt.
History
Early history
Alfred Angas Scott, founder of The Scott Motorcycle Company, designed a motorcycle with unit construction for the engine and gearbox. Production of the motorcycle began in 1908.[2]
In 1911, Singer offered motorcycles with unit-construction 299cc and 535cc engines.[3]
In 1914, ABC founder Granville Bradshaw designed a unit-construction horizontally opposed ('flat') twin for Sopwith Aircraft, who, at the time, also made motorcycles.[4]
In 1920 Carlo Guzzi constructed the G.P. 500 prototype with unit-construction. This was followed in 1921by the first Moto Guzzi production model, the "Normale", also a 500cc unit-construction motorcycle.[citation needed]
In 1921, an expanding Bianchi (Italy) showed its first unit-construction side-valve 600cc V-twin.[7]
In 1923, Rover introduced a 250cc unit-construction model, followed by a 350cc in 1924, but production ended in 1925.[8]
In 1923, the advanced three-speed Triumph single-cylinder 346cc sv unit-construction Model LS appeared, but did not sell well, and ended production in 1927.[7]
In 1923, BMW released its own unit construction shaft drive flat twin of 498cc. BMW has never built a motorcycle with a separate gearbox.[9]
From 1924, FN single-cylinder engines changed from semi unit construction (as seen in the last semi-unit single, the 1922 FN 285TT, in its last year of sale in 1924,) to unit construction engines (as seen in the new-for-1924 M.60).[10]
In 1928, BSA made their first and only two-stroke, a 175cc unit construction bike, for only one season, otherwise four-stroke twins became unit construction in 1962.[11]
The 1930 Triumph 175cc Model 'X' two-stroke, two-speed is their first "all-unit construction" two-stroke single-cylinder engine.[7]
From 1932, New Imperial was known for pioneering innovations in unit construction on motorcycles . They made the Unit Minor 150 and Unit Super 250 in this manner and by 1938 all of their machines were unit construction.[12][13]
In 1938, Francis-Barnett offered a 125cc unit-construction Snipe.[14]
In 1946, the Series B Vincent employed unit construction and used the engine-gearbox as a stressed member of the frame.[15]
The 1947 Sunbeam S7, an advanced overhead-cam, longitudinal twin, unit construction motorcycle, designed by Erling Poppe, used shaft drive.[3]
In 1957 the Royal Enfield Clipper was replaced by the unit-construction Crusader.[8]
In 1957 the first unit construction twin cylinder motorcycle made by Triumph, the 350cc (21 ci) 'Twenty One' 3TA, designed by Edward Turner and Wickes, was introduced for the 21st Anniversary of Triumph Engineering Co. Ltd. Unfortunately it also had the first "bathtub" rear enclosure, which proved a sales failure.[16]
Triumph unit-construction engineTriumph T110 with pre-unit-construction engine
Triumph Motorcycles produced its first single-cylinder unit construction model with the 149cc Terrier launched in 1952. It was quickly followed by the more popular 196cc Tiger Cub in 1953.[17] They made the first twin-cylinder unit construction model in 1957 with the release of the 350cc Twenty One 3TA (so named because it was approximately twenty-one cubic inches capacity).[18] The 500cc Triumph 5TA followed, and the 650cc models were made unit construction in 1963.[19] The 1963—1969 unit construction 650cc Triumph Bonneville has become sought- after models, partly as the 1970-onward oil-in-frame chassis was considered inferior.
The BSA Bantam range of two-stroke engines introduced the unit construction concept to BSA since its introduction in 1949. BSA produced their first four-stroke unit construction singles in 1959 when they introduced the C15 to replace the venerable c12 single. The unit construction (in contrast to the separate engine and gearbox of the C10/C11 and c12) gave the family of motorcycles started by this model its familiar name.
The C15 was intended as a utility "get to work" model, and served this purpose faithfully for many thousands of users. It was a simple and reasonably robust design.
Along with the C15 came the B40, the 350cc version. This was no faster than the C15, but had a little more lugging power. A version of the B40 was also produced (in considerable quantities) for various branches of the military. These motorcycles (known as the "Ex-WD B40") were more rugged than the vanilla version (in particular, the timing-side main bearing was over- rather than under-engineered and an oil filter was fitted), slightly de-tuned and given a version of the competition frame. For these reasons, these bikes can make very good buying, and are often used as the basis for competition machines.
Several minor changes were made to the C15 in 7 years (with some variations on the theme - the "warmer" SS80 and SS90, plus competition versions).
In 1967 the model underwent some revisions and a name change to B25. The model then continued with little variation until BSA collapsed in the early 1970s.
The BSA unit single was an affordable introduction to motorcycling for many young men in the 1960s and 1970s. The simple design meant that inexperienced and under-equipped home mechanics could keep them running under most circumstances. The effects of such inexperienced maintenance led to a slightly undeserved reputation for unreliability - a well maintained and regularly serviced unit single will chug along for a very long time with no problems.
The warmer versions (such as the much-loved Starfire) were generally less robust, but their light weight, enjoyable handling and peppy engines meant that many people considered the hours of necessary maintenance a worthwhile trade-off.
Many BSA unit singles were built, meaning there are few 1960s motorcycles with such a large supply of readily available spares. The tunability and ready supply of these motors, combined with their compact and light(ish) construction has also made them a popular choice for modern "Classic" competition.
The BSA design was based on the Triumph Tiger Cub, first produced in 1952. The continuation of the model until 1973 speaks well for the popularity and utility of this design, but also reflects badly on the forward-thinking and investment of the BSA management. By 1967 unit singles were looking slow and rattly and the "charm" of the traditional British oil-leak was wearing thin. The new breed of Japanese motorcycles arriving on the scene were fast and exotic in comparison, and the buying public can certainly not be blamed for their eventual shunning of the entire British motorcycle industry.
Triumph Engineering Co Ltd was a British motorcycle manufacturing company, based originally in Coventry and then in Meriden. A new company, Triumph Motorcycles Ltd, based in Hinckley, gained the name rights after the end of the company in the 1980s and is now one of the world's major motorcycle manufacturers.
Matchless is one of the oldest marques of British motorcycles, manufactured in Plumstead, London, between 1899 and 1966. A wide range of models were produced under the Matchless name, ranging from small two-strokes to 750 cc four-stroke twins. Matchless had a long history of racing success; a Matchless ridden by Charlie Collier won the first single-cylinder race in the first Isle of Man TT in 1907.
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 Triumph Trident and BSA Rocket 3 was a technically advanced, high-performance roadster motorcycle made by Triumph Engineering and BSA from 1968 to 1975, and sold under both the Triumph and BSA marques. Alongside the Honda CB750, and later the Kawasaki triples, it brought a new level of sophistication to street motorcycles, marking the beginning of the superbike era. The Honda CB750 overshadowed the Trident to be remembered as the 'first superbike', in spite of the Triumph Trident actually debuting before the Honda by a few weeks.
Douglas was a British motorcycle manufacturer from 1907–1957 based in Kingswood, Bristol, owned by the Douglas family, and especially known for its horizontally opposed twin cylinder engined bikes and as manufacturers of speedway machines. The company also built a range of cars between 1913 and 1922.
Pre-unit construction, also called separate construction, is a motorcycle engine architecture where the engine and gearbox are separate components with their own oil reservoirs, linked by a driving chain within a primary chaincase. Mounting plates are usually attached to the frame allowing for chain adjustment by gearbox fore-and-aft movement and via screw adjusters and elongated mounting holes. Even though Singer offered an integrated engine and gearbox in a single casing in 1911, it was not until the 1950s that technical advances meant it was possible to reliably construct engines with integral gearboxes in a single unit, known as unit construction.
Edward Turner was an English motorcycle designer. He was born in Camberwell in the London Borough of Southwark, on the day King Edward VII was proclaimed King. In 1915, Turner had his first ride on a motorcycle, a Light Tourist New Imperial.
The history of the motorcycle begins in the second half of the 19th century. Motorcycles are descended from the "safety bicycle," a bicycle with front and rear wheels of the same size and a pedal crank mechanism to drive the rear wheel. Despite some early landmarks in its development, the motorcycle lacks a rigid pedigree that can be traced back to a single idea or machine. Instead, the idea seems to have occurred to numerous engineers and inventors around Europe at around the same time.
BMW Motorrad is the motorcycle brand of BMW, part of its Corporate and Brand Development division. It has produced motorcycles since 1923, and achieved record sales for the fifth year in succession in 2015. With a total of 136,963 vehicles sold in 2015, BMW registered a growth of 10.9% in sales in comparison with 2014. In May 2011, the 2,000,000th motorcycle produced by BMW Motorrad was an R1200GS.
The BSA Royal Star was a Birmingham Small Arms Company (BSA) motorcycle whose new engine design paved the way for a range of successful unit construction twins. As well as giving a clean look to the engine, with the pushrod passages part of the cylinder block casting, unit construction reduced the number of places oil could leak from.
The Triumph Tiger Cub was a 200 cc (12 cu in) single-cylinder British motorcycle made by Triumph Motorcycles at their Meriden factory. It wased on the Triumph T15 Terrier 150 cc, itself a surprise announcement just before the 1952 show, the 200 cc T20 Tiger Cub designed by Edward Turner, and launched at the Earls Court show in November 1953 competed well against the other small-capacity motorcycles of the time, such as those using Villiers two-stroke engines.
The BSA A7 was a 500cc motorcycle model range made by Birmingham Small Arms Company (BSA) at their factory in Armoury Road, Small Heath, Birmingham. The range was launched in 1946 using a 495 cc (30.2 cu in) long stroke engine. An improved 497 cc (30.3 cu in) version based on the BSA A10 engine was launched in 1950. The various A7 models continued in production with minor modifications until 1961/2 when they were superseded by the unit-construction A50 model.
The BSA C15 was a 250 cc single-cylinder ohv motorcycle manufactured by the British company BSA from September 1958 until 1967, and was BSA's first four-stroke unit-construction bike. For most of that period, after the introduction of 'Learner Laws' in 1961, a 250 cc was the largest capacity solo machine that a learner could ride unaccompanied when displaying L-plates in the United Kingdom. A road-going Sports derivative was added in 1961, and off-road versions, for Trials and Scrambles, were also available in the range.
The BSA B50 was a single-cylinder 499 cc (30.5 cu in) ohv motorcycle, produced by BSA at their factory in Small Heath, Birmingham. The last of the big capacity unit-construction singles from the Birmingham Small Arms company, it had an alloy engine with a bore of 84 mm (3.3 in) and a stroke of 90 mm (3.5 in). As well as the road version, special models were produced for off-road competition use.
The BMW R2 was a 198 cc overhead valve single-cylinder motorcycle produced by BMW between 1931 and 1936, the smallest motorcycle ever to enter series production with the firm. Despite its much smaller design and engine capacity, the R2 retained many features of the larger boxer twin motorcycles in the range, such as cardan shaft drive and a pressed-steel duplex frame. The R2 was the smallest in the range of singles produced during the 1930s by BMW, with its big brothers being the 305 cc R3 and the 400 cc R4.
BSA motorcycles were made by the Birmingham Small Arms Company Limited (BSA), which was a major British industrial combine, a group of businesses manufacturing military and sporting firearms; bicycles; motorcycles; cars; buses and bodies; steel; iron castings; hand, power, and machine tools; coal cleaning and handling plants; sintered metals; and hard chrome process.
The BSA unit twins were a range of unit construction twin-cylinder motorcycles made by the Birmingham Small Arms Company (BSA) and aimed at the US market. A range of 500 cc (31 cu in), 650 cc (40 cu in) and 750 cc (46 cu in) twins were produced between 1962 and 1972, but they were really developments of the older pre-unit A7/A10 model range with less weight. The engines had a reputation for vibration, but acceleration was good for the time, to a top speed of 100 miles per hour (160 km/h).
The BSA A10 series was a range of 646 cc (39.4 cu in) air-cooled parallel twin motorcycles designed by Bert Hopwood and produced by Birmingham Small Arms Company at Small Heath, Birmingham from 1950 to 1963. The series was succeeded by the A65 unit construction models.
The Norton Model 7 Dominator was a 500 cc vertical twin motorcycle manufactured by the Norton Motorcycle Company from 1949 to 1955. It was the first of Norton's Dominator range of motorcycles. The engine was designed by Bert Hopwood and was a departure from Norton's previous practice of producing single-cylinder machines. The Model 7 was used in Japan as a police motorcycle.
The Norton Model 99 Dominator was a 600 cc vertical twin motorcycle manufactured by the British Norton Motorcycle Company at their Bracebridge St, Birmingham factory from 1956 to 1962. The 99 was based on the 500 cc Model 88 Dominator with an enlarged engine. The model was superseded by the 650SS.
References
↑ Lucas was then the major British manufacturer of automotive electric components.
↑ "Discovering Yorkshire". Archived from the original on 2007-09-30. Retrieved 2008-10-05. DiscoveringYorkshire Scott's early motorcycle developments (Retrieved 25 November 2006)
1 2 IanChadwick Brit Bikes S (Retrieved 25 November 2006)
1 2 IanChadwick Brit Bikes A (Retrieved 25 November 2006)
↑ Hatfield, Jerry (2002). "The Flathead Era". In Holmstrom, Darwin (ed.). The Harley-Davidson Century. St. Paul, MN USA: MBI Publishing. pp.48–49. ISBN0-7603-1155-2. The Sport, the first American middleweight with an opposed-cylinder configuration, featured other innovations for the American market, including unit construction of the engine and three-speed transmission, helical gear primary drive, and a wet clutch.
↑ Triumph Motorcycles timeline: 1963-1972: The Glory Years
This page is based on this Wikipedia article Text is available under the CC BY-SA 4.0 license; additional terms may apply. Images, videos and audio are available under their respective licenses.
