Editing Straight-twin engine (section)

== Usage in motorcycles ==
===History===
[[File:Triumph Speed Twin.jpg|thumb|1938–1966 [[Triumph Speed Twin]] ]]
[[File:Quail Motorcycle Gathering 2015 (17135471883).jpg|thumb|1973–1975 [[Yamaha RD350]] two-stroke motorcycle]]

The world's first production motorcycle, the 1894 [[Hildebrand & Wolfmüller]] used a straight-twin engine. The cylinders lay flat and forward-facing, with the pistons connected directly to the rear wheel using a locomotive-style connecting rod. In 1903, the [[Werner Motors|Werner Motocyclette]] became the second production motorcycle model, using a straight-twin engine with vertical cylinders. The Werner engine uses cast-iron cylinders with integral heads, side valves and has a displacement of 500&nbsp;cc.<ref>http://www.moto-histo.com/france/fr1/fr1.htm|Motos Francaises, Werner Brothers Moto Bicyclettes</ref>

The 1938 [[Triumph Speed Twin]] was a successful straight-twin motorcycle which also led to straight-twin engines becoming more widely used by other brands. The engine was designed by [[Edward Turner (motorcycle designer)|Edward Turner]] and [[Val Page]], and was initially used in the 1933 [[Triumph 6/1]] sidecar hauler (which won the [[International Six Days Enduro|International Six Days Trial]] silver medal and the 1933 [[Maudes Trophy]]).<ref>{{cite web |url= http://www.motorcycleclassics.com/classic-british-motorcycles/triumph-6-1-zm0z13mjzbea.aspx?PageId=2#ArticleContent|title= Triumph's First Twin: Triumph 6/1|last1= Davis|first1= Simon|date= May–June 2013|website= Motorcycle Classics|publisher= Ogden Publications|location= Topeka, Kansas, USA|access-date= 2014-04-26|page=2}}</ref> During the development of the engine, it was found that a 360 degree crank angle was better suited to the use of a single carburettor than a 180 degree crank angle.<ref>{{cite web |url= http://www.motorcycleclassics.com/classic-british-motorcycles/triumph-6-1-zm0z13mjzbea.aspx#axzz2zzmFO38W|title= Triumph's First Twin: Triumph 6/1|last1= Davis|first1= Simon|date= May–June 2013|website= Motorcycle Classics|publisher= Ogden Publications|location= Topeka, Kansas, USA|access-date= 2014-04-26|page=1}}</ref>

Following the trend created by the Triumph Speed Twin, the most common design used by British motorcycle manufacturers until the mid-1970s was a four-stroke straight-twin engine with a 360 degree crankshaft.<ref name="Setright, Parallel twin" /><ref name="TriumphPassion" /> The manufacturers producing these motorcycles included [[Birmingham Small Arms Company|BSA]], [[Norton Motorcycle Company|Norton]], [[Triumph Engineering|Triumph]], [[Ariel Motorcycles|Ariel]], [[Matchless]] and [[AJS]]. Straight-twin engines were also produced by Italian and German manufacturers,<ref name="Wilson1995p53" /><ref name="BaconDominator" /><ref name="ParallelUniverse" /> along with the American manufacturer [[Indian Motocycle Manufacturing Company|Indian]].<ref name="Wilson1995pp108_9" />

In 1949, the [[AJS Porcupine|AJS E-90 Porcupine]] won the 500&nbsp;[[1949 Grand Prix motorcycle racing season|1949 Grand Prix World Championship]], becoming the first and only straight-twin motorcycle to win the championship. This engine is one of few four-stroke straight-twins to use cylinders oriented horizontally rather than vertically.<ref name="parallel-twin" />

Since the 2000s, BMW and several Japanese manufacturers have continued to produce straight-twin engines, mostly for middleweight models.<ref name="ClarkeMMT" /> Several large [[Scooter (motorcycle)|scooters]] have also used straight-twin engines, such as the 2001 [[Yamaha TMAX]]<ref name="MCN_TMax" /> and the 2001 [[Honda Silver Wing (scooter)|Honda Silver Wing]].<ref name="MotorcycleSilverWingTest" /> Straight-twin engines are also used in motocross sidecar racing.<ref name="WestlakeGiants" />

=== Transverse-engined models ===
[[File:NortonCommandoMKIIA.jpg|thumb|1973 [[Norton Commando|Norton Commando Interstate]] ]]

Many large British motorcycles from 1945 to the 1960s used a straight-twin [[transverse engine]] (i.e. oriented with the crankshaft perpendicular to the frame), such as the [[Triumph Bonneville]] and [[Norton Commando]]. This layout is well suited to air-cooling, since both cylinders receive equal airflow and the exhaust can exit in the well-cooled location at the front of each cylinder.<ref>{{Citation |last1=Coombs |first1=Matthew |last2=Haynes |first2=John |last3=Shoemark |first3=Pete |title=Motorcycle Basics | edition=2nd |publisher=Haynes | year=2002| page=1•31| isbn= 978-1-85960-515-8 | url=https://books.google.com/books?id=D0DhHAAACAAJ}}</ref>

The transverse-engine straight-twin design has been largely replaced by [[V-twin engine]]s; however, the straight-twin design has the advantage of easier packaging of ancillaries (such as the air-filter, carburettor and ignition components), which also improves access to ancillaries for maintenance/repairs.<ref>"Fast Bike" magazine August 1995 page 20</ref> A straight-twin engine using a 270 degree crankshaft can have a similar sound and feel to a V-twin engine with an uneven firing order.
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=== Longitudinal-engined models ===
[[File:Sunbeam S8 1951.jpg|thumb|1951 [[Sunbeam S7 and S8|Sunbeam S8]] ]]

[[Longitudinal engine]] straight-twin motorcycles are less common; however, examples include the 1930–1938 [[Dresch|Dresch Monobloc]]<ref>{{cite web |title=Dresch Monobloc 1930 500cc 2 cyl sv |url=https://www.classic-motorcycle.com/Content/Bike/dresch-monobloc-1930-500cc-2-cyl-sv/a0002 |website=www.classic-motorcycle.com |access-date=13 October 2020}}</ref> and the 1949–1956 [[Sunbeam S7 and S8]].<ref>487 cc Sunbeam. Walneck's Classic Cycle Trader, Dominion Enterprises, Dec 1996 reprinted from Classic Bike Magazine, 5 January 1950.</ref><ref name="DealerNewsNov1996" />

This engine orientation allows for a motorcycle as narrow as a single-cylinder engine,<ref name="MDATHandbook" /> which reduces the aerodynamic drag, especially for the purpose of motorcycle racing. However, the main disadvantage for air-cooled engines is that the rear cylinder runs hotter than the front cylinder.<ref name="heavy" /><ref name="UltiHistFast" />
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