View source for BMW R51/3

{{refimprove|date=January 2013}}
{{Infobox motorcycle
| name             = BMW R51/3
| image            = R51-3-left.jpg
| alt              =
| caption          = A 1952 R51/3 – note the half-width brakes before 1954
| aka              =
| manufacturer     = BMW
| parent_company   =
| production       = 1951-5
| assembly         =
| predecessor      =
| successor        =
| class            =
| engine           = 494cc four-stroke flat-twin
| bore_stroke      = {{convert|68|x|68|mm|2|abbr=on}}
| compression      = 6.3:1
| top_speed        = 140 km/h
| power            = 24 hp
| torque           =
| ignition         = Magneto
| transmission     = Single-plate dry clutch, 4-Speed manual
| frame            =
| suspension       = Front telescopic forks, rear plunger
| brakes           = 200mm drums
| tires            =
| rake_trail       =
| wheelbase        = 1400mm
| length           = 2130mm
| width            = 790mm
| height           = 985mm
| seat_height      =
| dry_weight       =
| wet_weight       = 190 kg
| fuel_capacity    = 17 L
| oil_capacity     = 2 L
| fuel_consumption = 4.5L/100KM
| turning_radius   =
| related          =
| sp               =
| footnotes        =
}}
[[File:BMW R 51-3 motorcycle 1951 - 3.jpg|thumb|right|1951 R51/3 at the BMW Museum]]
[[File:BMW_R67-3.jpeg|thumb|left|1955 BMW R67/3]]
[[File:Cylinder-fins-comparison.jpg|right|thumb|An R51/3 has eight round cylinder fins (left); the R67-R67/3 have nine larger and pointed cylinder fins (right)]]
[[File:R51-plunger.jpg|thumb|Note the exposed driveshaft and ''plunger'' [[Suspension (motorcycle)#Rear suspension|rear suspension]]]]
The '''BMW R51/3''' was [[BMW Motorrad|BMW]]'s second post-[[World War II]] 500&nbsp;cc [[motorcycle]], following the briefly produced R51/2. It featured a [[flat-twin engine]] and exposed [[drive shaft]].<ref>{{Cite web |url=http://specials.bmw-motorrad.com/com/en/fascination/history/models_new/bmw_r51_3_data.html |title=R51/3 data sheet |access-date=2012-07-05 |archive-url=https://web.archive.org/web/20141031155629/http://specials.bmw-motorrad.com/com/en/fascination/history/models_new/bmw_r51_3_data.html |archive-date=2014-10-31 |url-status=dead }}</ref> In 1951, the R51/3 succeeded and modernized the 1950 R51/2, which was essentially a pre-war design that was produced after the war.  The 600&nbsp;cc R67, R67/2, and R67/3 series and the more sporting [[BMW R68|R68]] model also followed the R51/2.
==History==
Following World War II, Germany was precluded from producing motorcycles of any sort by the Allies. When the ban was lifted, in
Allied-controlled Western Germany, BMW had to start from scratch. There were no plans, blueprints, or schematic drawings. Company engineers had to use surviving pre-war motorcycles to create new plans. In 1948, it introduced the 250&nbsp;cc R24, which was essentially a pre-war R23, complete with rigid rear end.
When larger machines were permitted, [[BMW Motorrad|BMW]] introduced its R51/2 in 1950, a model that was in production for only one year and that was essentially a pre-war BMW produced after the war. The R51/3 was then introduced in 1951 for a production run of four years.
The 600&nbsp;cc R67, sister model to the R51/3 and almost identical visually, was also introduced in 1951, but it went through two revisions. The more powerful R67/2 came out one year later and was replaced in 1955 by the R67/3, which was in production through the 1956 model year.
In 1952, BMW introduced the 600&nbsp;cc R68,<ref>{{Cite web |url=http://specials.bmw-motorrad.com/com/en/fascination/history/models_new/bmw_r68_data.html |title=BMW R68 Data |access-date=2012-07-03 |archive-url=https://web.archive.org/web/20140808051210/http://specials.bmw-motorrad.com/com/en/fascination/history/models_new/bmw_r68_data.html |archive-date=2014-08-08 |url-status=dead }}</ref> which produced  {{convert|35|hp|kW|abbr=on}}, had a compression ratio of 8.0:1.
==Technical data==
[[File:R51-3-front.jpg|thumb|Front view of an R51/3]]
{| class="wikitable"
!
!R51/3
!R67 – R67/3
|-
!Design
| colspan="2" |Boxer [[Flat-twin|Flat Twin]]
|-
!Engine
| colspan="2" | Four-stroke [[Overhead valve|OHV]]
|-
!Model Years
| | 1951&ndash;1955
| | 1951&ndash;1956
|-
!Bore
| | 68&nbsp;mm / 2.68 in
| | 72&nbsp;mm / 2.83 in
|-
!Stroke
| | 68&nbsp;mm / 2.68 in
| | 73&nbsp;mm / 2.87 in
|-
!Displacement
| |{{convert|494|cc|cuin||abbr=on}}
| |{{convert|594|cc|cuin||abbr=on}}
|-
!Power
| |{{convert|24|hp|kW|abbr=on}} @ 5800&nbsp;rpm
| |{{convert|26|hp|kW|abbr=on}} / {{convert|28|hp|kW|abbr=on}} @ 5500&nbsp;rpm
|-
!Compression Ratio
| |6.3:1
| |5.6:1 / 6.5:1
|-
!Top Speed
| |140&nbsp;km/h (87&nbsp;mph)
| |150&nbsp;km/h (93&nbsp;mph)
|-
!Curb Weight
| colspan="2" | 190&nbsp;kg (419&nbsp;lb)
|-
!Gross Vehicle Weight
| colspan="2" | 355&nbsp;kg (783&nbsp;lb)
|-
!Fuel Tank Capacity
| colspan="2" | {{convert|17|L|abbr=on}}
|}
==See also==
* [[History of BMW motorcycles]]
* [[Motorcycle fork]]
* [[BMW R68]]
*[[List of motorcycles of the 1950s]]
==References==
{{reflist}}
==External links==
{{commons cat inline|BMW R51}}
{{BMW motorcycles}}
{{DEFAULTSORT:BMW R51 3}}
[[Category:BMW motorcycles|R51 3]]
[[Category:Motorcycles powered by flat engines]]
[[Category:Shaft drive motorcycles]]
[[Category:Motorcycles introduced in the 1950s]]