View source for Engineering:BSA B25

{{short description|Series of motorcycles made by the Birmingham Small Arms Company}}
{{Infobox motorcycle
| name             = BSA B25
| image            = File:BSA Starfire 250cc (1969) - 29927122245.jpg
| alt              = 
| caption          = 1969 BSA Starfire
| aka              = 
| manufacturer     = BSA motorcycles
| parent_company   = Birmingham Small Arms Company Limited
| production       = 1967–1971
| assembly         = Small Heath, Birmingham, UK
| predecessor      = [[Engineering:BSA C15|BSA C15]]
| successor        = 
| class            = 
| engine           = {{cvt|247|cc|abbr=on}}, [[Engineering:Air-cooled engine|air-cooled]], [[Engineering:Unit construction|unit construction]], [[Engineering:Overhead valve engine|OHV]], four-stroke, [[Engineering:Single-cylinder engine|single]] 
| bore_stroke      = {{cvt|67|x|70|mm|abbr=on}}
| compression      = 10:1
| top_speed        = 
| power            = {{convert|26|bhp|kW|abbr=on}} at 7250 rpm
| torque           = 
| ignition         = 
| transmission     = [[Engineering:Clutch#Wet vs. dry systems|Wet]], [[Engineering:Clutch#Multiple plate clutch|multi-plate clutch]], 4-speed gearbox, [[Physics:Chain drive|chain drive]]
| frame            = [[Engineering:Motorcycle frame#Single cradle|Single cradle]]
| suspension       = Front: [[Engineering:Telescopic fork|telescopic fork]]s<br />Rear: [[Engineering:Swingarm|swinging arm]]
| brakes           = [[Engineering:Drum brake|Drum brake]]s front & rear
| tires            = 
| rake_trail       = 
| wheelbase        = 
| length           = 
| width            = 
| height           = 
| seat_height      = 
| dry_weight       = 
| wet_weight       = 
| fuel_capacity    = 
| oil_capacity     = 
| fuel_consumption = 
| turning_radius   = 
| range          = 
| related          = 
| sp               =  uk
| footnotes        ={{sfn|Wright|1992}}{{sfn|Richmond|1967}}{{sfn|Henshaw|2015}}
}}
The '''BSA B25''' was a series of {{convert|250|cc|abbr=on}} [[Engineering:Unit construction|unit construction]] single-cylinder [[Engineering:Overhead valve engine|OHV]] four-stroke [[Engineering:Motorcycle|motorcycle]]s made by the [[Company:Birmingham Small Arms Company|Birmingham Small Arms Company]]. Developed from the [[Engineering:BSA C15|BSA C15]], the machines were produced between 1967 and 1971.<ref name="BSAOC Year Listing">{{cite web|title=BSAOC Year Listing |url=https://www.bsaownersclub.co.uk/yearlisting.html |website=www.bsaownersclub.co.uk |publisher=Owners Club |access-date=5 October 2019|archive-url=https://web.archive.org/web/20191007184757/https://www.bsaownersclub.co.uk/yearlisting.html|archive-date=7 October 2019}}</ref> The B25 was the fastest British production 250.{{sfn|Wright|1992|p=145}}

==Technical details==
The 247 cc engine was a higher performance development of that used the existing C15. [[Engineering:Bore (engine)|Bore]] and [[Engineering:Stroke (engine)|stroke]] of 67 x 70&nbsp;mm was retained,{{sfn|Richmond|1967|p=118}} but a new alloy [[Physics:Cylinder (engine)|barrel]] and [[Engineering:Cylinder head|cylinder head]] were introduced featuring square fins.{{sfn|Richmond|1967|p=116}}{{sfn|Savadori|2007}} The pushrod tunnel was cast into the barrel rather than being a separate item as on earlier models. [[Physics:Tappet|Tappet]] adjustment was by eccentric [[Engineering:Rocker arm|rocker]] shaft.<ref>{{cite web |title=B25 Starfire B44 Shooting Star Models Workshop Manual |url=https://www.bsaunitsingles.com/Archives/Owners_Manuals/B25SS%20B44SS%201969-70%20Workshop%20Manual%2000-4176%20x.pdf |website=www.bsaunitsingles.com |publisher=BSA Motor Cycles Ltd |access-date=5 October 2019 |page=B6}}</ref>

To improve performance the inlet tract was opened{{sfn|Richmond|1967|p=116}} up and bigger valves fitted{{sfn|Henshaw|2015|p=11}} along with the newly introduced Amal Concentric carburettor.{{sfn|Richmond|1967|p=118}} Compression ratio was increased to 10:1{{sfn|Henshaw|2015|p=11}} and a sports [[Engineering:Camshaft|camshaft]] used. Power output was {{convert|26|bhp|kW|abbr=on}} at 7250 rpm, (later reduced to {{convert|22.5|bhp|kW|abbr=on}} on the P34 models{{sfn|Henshaw|2015|p=12}}) The engine was free-revving and would rev to over 8,000 rpm.{{sfn|Henshaw|2015|p=11}}

Unlike the later C15s, which used a roller bearing big end, the B25 reverted to a plain big end and split conrod.{{sfn|Henshaw|2015|p=11}}{{sfn|Reynolds|1990|p=48}} The model gained a reputation for unreliability due to big end and conrod failures. BSA attempted to address this in the P34 models by fitting a conrod with a larger shoulder. The [[Engineering:Oil pump (internal combustion engine)|oil pump]] was also changed to a [[Chemistry:Cast iron|cast iron]] body design, the earlier zinc alloy bodies tending to distort and reduce [[Engineering:Oil pressure|oil pressure]].{{sfn|Jones|2014|p=68}} An inline paper [[Engineering:Oil filter|oil filter]] was also added to improve oil quality.{{sfn|Henshaw|2015|p=12}}

A [[Engineering:Roller chain|duplex chain]] took power to a [[Engineering:Clutch#Wet vs. dry systems|wet]], [[Engineering:Clutch#Multiple plate clutch|multi-plate clutch]]. The [[Engineering:Motorcycle transmission|gearbox]] had 4 speeds and final drive was by [[Physics:Chain drive|chain]].{{sfn|Savadori|2007}}

Developed from the competition C15s,{{sfn|Henshaw|2015|p=12}} the all-welded [[Engineering:Motorcycle frame|frame]] had a single downtube that split into two to form a cradle under the engine.{{sfn|Savadori|2007}} The later P34 used a frame where the oil was stored in the top spine,{{sfn|Jones|2014|p=66}} this frame was shared with the [[Engineering:BSA B50|B50 models]].{{sfn|Jones|2014|p=103}}

Electrics were upgraded to 12v (the C15 used a 6v system).{{sfn|Henshaw|2015|p=12}} The output from the [[Engineering:Alternator (automotive)|alternator]] was regulated by a [[Physics:Zener diode|zener diode]] with a large heat sink mounted between the front forks.{{sfn|Richmond|1967|p=117}}

==B25 Starfire/C25 Barracuda==
The first model of the series was introduced in 1967 as the '''C25 Barracuda''' in the UK and the '''B25 Starfire''' in the USA{{sfn|Henshaw|2015|p=11}} (although the US models had frame and engine numbers prefixed C25).{{sfn|Henshaw|2015|p=57}} The model was a more sporty replacement for the C15 and, in the UK, aimed at learner riders.{{sfn|Henshaw|2015|p=11}}

Sharing many cycle parts with the 441 cc B44 Victor Roadster,{{sfn|Henshaw|2015|p=15}}{{sfn|Richmond|1967|pp=116,118}} the model had a {{convert|2|USgal|impgal}} fibre glass tank and a seat with a rear hump.{{sfn|Richmond|1967|p=118}} Front [[Engineering:Telescopic fork|forks]] were two-way damped and rubber gaiters fitted instead of the metal covers of the C15 and at the rear the springs of the [[Engineering:Shock absorber|shock absorber]]s were now exposed. Chrome mudguards and a chrome headlight shell was fitted. Single-sided {{convert|7|in|mm}} [[Engineering:Drum brake|drum brake]]s were fitted front and rear.{{sfn|Savadori|2007}}

;1968

The B25 Starfire designation was adopted for all markets<ref name="BSAOC Year Listing" /> (Frame and engine numbers being prefixed B25B).{{sfn|Henshaw|2015|p=58}} The machine gained a full-width 7" front brake,{{sfn|Savadori|2007}} and larger petrol tanks fitted; {{convert|2.5|USgal|impgal}} on the US version<ref name="1968 USA BSA Catalog">{{cite web|title=1968 USA BSA Catalog |url=http://www.bsansw.org.au/BSA2016/catalogues/1968-us-catalog/68p12/ |publisher=BSA MCC of NSW |access-date=5 October 2019 |language=en-AU}}</ref> and a steel {{convert|3.4|impgal|USgal}} on the UK version.<ref>{{cite web|title=B25 Starfire B44 Shooting Star Models Workshop Manual |url=https://www.bsaunitsingles.com/Archives/Owners_Manuals/B25SS%20B44SS%201969-70%20Workshop%20Manual%2000-4176%20x.pdf |website=www.bsaunitsingles.com |publisher=BSA Motor Cycles Ltd |access-date=5 October 2019 |page=GD12}}</ref>

;1969

In common with other machines in the BSA/Triumph range, a new 7" twin leading shoe front brake was fitted.{{sfn|Henshaw|2015|p=11}} Minor cosmetic changes included rubber knee pads on the tank and a chrome passenger grab-rail. The US model was given a high-level [[Engineering:Exhaust system|exhaust]] and the cylinder and cylinder head finished in black.<ref name="1969 USA BSA Catalog">{{cite web |title=1969 USA BSA Catalog |url=http://www.bsansw.org.au/BSA2016/catalogues/1969-us-catalog/69-4/ |publisher=BSA MCC of NSW |access-date=5 October 2019 |language=en-AU}}</ref> Engine and frame numbers were prefixed B25S.{{sfn|Henshaw|2015|p=58}}

==B25FS Fleetstar==
[[File:BSA Fleetstar B25FS (1968) - 29843848861.jpg|thumb|1968 BSA Fleetstar]]
A less sporty version, the '''B25FS Fleetstar''', was introduced in 1969 to appeal to fleet customers such as the police. The compression ratio was reduced to 8.5:1, which dropped power output down to {{convert|21|bhp|kW|abbr=on}}.{{sfn|Henshaw|2015|p=12}} The machine had painted, valance mudguards and a more conventional steel tank.<ref>{{cite magazine|author=<!--Staff writer(s); no by-line.--> |title=Whats A BSA Fleetstar Then? |url=https://www.pressreader.com/uk/classic-bike-uk/20190101/282965336129569 |magazine= Classic Bike |date= 1 January 2019 |via=Press Reader}}</ref> Various accessories such as [[Engineering:Motorcycle fairing|fairings]], leg-guards and panniers could be fitted dependent on the purchaser's requirements.{{sfn|Jones|2014|p=29}}

The machine was updated with the oil bearing frame in 1971, but unlike the other B25 models retained its roadster styling. Around 449 Fleetstars were manufactured, about 250 these being sold to the police.<ref>{{cite web |title=BSA B25 Fleetstar (Starfire) 1968: The Aquisition [sic&#93;; my BSA B25 Starfire Project |url=http://bsab25maybe.blogspot.com/2016/01/the-aquisition-my-bsa-b25-starfire.html |publisher=bsab25maybe |access-date=5 October 2019 |date=27 January 2016}}</ref>

==B25 Woodsman==
The '''B25 Woodsman''' variant with a high-level exhaust was produced alongside the standard model for non-US markets (the US model having a high level exhaust). The model was soon withdrawn and only about 10 machines were made.{{sfn|Ratio|2014}}

==P34 (oil-in-frame) models==
[[File:BSA B25 Victor 250.jpg|thumb|1971 BSA Victor Trail 250]]

Since the late 1960s, BSA engineers had been working on a revamp of the existing range and development of new models. In October 1970, the new range, collectively known as ''The Power Set'', was released. The revamp was divided into individual projects. The singles project, which consisted of the 250 cc B25 and a new 500 cc [[Engineering:BSA B50|B50]], was code-named P34.{{sfn|Jones|2014|pp=6-7}}

The engine received some upgrades. Failures of the conrod was addressed by redesigning the conrod with a larger shoulder section. This required the crankshaft to be machined to clear the thicker conrod. Being a [[Engineering:Plain bearing|plain bearing]], the big end requires a good flow of oil. A new cast iron bodied oil pump was fitted, the previous zinc alloy bodied pump was prone to warping leading to reduction in oil pressure. A new full-flow paper oil filter was also fitted. These modifications were intended to reduce the tendency for the big end to fail.{{sfn|Jones|2014|pp=67-68}} Power output was reduced to {{convert|22.5|bhp|kW|abbr=on}}.{{sfn|Henshaw|2015|p=12}}

The mating surfaces between the barrel and cylinder head were made larger and a new [[Engineering:Head gasket|head gasket]] designed. Rocker box mounting studs were increased in size. A thrust washer was placed between the clutch chain-wheel and its mounting to reduce wear problems. A redesigned clutch hub allowed an extra plate to be fitted. The rear engine mounting lug was increased to 75&nbsp;mm for consistency with the 500 engine.{{sfn|Jones|2014|p=68}}

The all-new cycle parts were shared with the B50, and many of the components were common to the complete BSA/Triumph range.{{sfn|Jones|2014|pp=64-67}} The frame, which held the oil in the top tube, was developed from the competition machines.{{sfn|Henshaw|2015|p=12}} A new high-level lozenge shaped box silencer was fitted, which was designed to meet possible future more stringent noise laws.{{sfn|Brooke|Gaylin|2017|p=159}} Common to the rest of the BSA/Triumph range were the Ceriani type forks and conical wheel hubs. The hubs were 7" rear and either 6" sls or 8" tls front.{{sfn|Jones|2014|pp=64-67}}

These models were only in production for a year. The financial situation of the BSA Group forced a great reduction in the model range for 1972 and the 250s were discontinued.{{sfn|Brooke|Gaylin|2017|p=160}}

===B25SS Gold Star 250===
The '''B25SS Gold Star 250''' was marketed as an on or off-road machine.<ref name="Catalog - Gold Star 250-SS">{{cite web |title=1971 USA BSA Catalog - Gold Star 250-SS |url=http://www.bsansw.org.au/BSA2016/catalogues/1971-us-catalog/71r9/ |publisher=BSA MCC of NSW |access-date=6 October 2019 |language=en-AU}}</ref> The UK versions had the 8" tls front brake and a longer front mudguard to accommodate a front [[Vehicle registration plate|number plate]], which was required by UK at this time. The US version had the 6" sls front brake and a 6" shorter front mudguard. Both variants had a steel {{convert|2|impgal|USgal}} petrol tank with a twist-off filler cap.{{sfn|Jones|2014|pp=65-67}} The machine was fitted with 18" wheels.<ref name="Catalog - Gold Star 250-SS" />

===B25T Victor Trail 250===
Marketed as an off-road machine, the '''B25T Victor Trail 250'''<ref name="Catalog - Gold Star 250-SS" /> used most of the components of the 250 Gold Star. The most significant changes were an alloy petrol tank, front mudguard mounted on the bottom fork yoke,{{sfn|Jones|2014|pp=65-67}} a 20" front wheel and off-road tyres, the rear being a larger 400 section.<ref name="Catalog - Victor 250-Trail">{{cite web |title=1971 USA BSA Catalog - Victor 250-Trail |url=http://www.bsansw.org.au/BSA2016/catalogues/1971-us-trail-catalog/71d-7/ |publisher=BSA MCC of NSW |access-date=6 October 2019 |language=en-AU}}</ref> The 6" sls front brake was used on both the UK and US variants.{{sfn|Jones|2014|pp=65-67}}

==Triumph variants==
[[File:Triumph 250 Trophy TR25W.jpg|thumb|1970 Triumph TR25W Trophy]]

===TR25W Trophy===
Triumph Engineering had been bought by BSA in 1951 but had retained its own identity and had a separate model range.<ref>{{cite web |title=Triumph Motorcycle History: History of Triumph |url=https://www.motorcycle.com/manufacturer/history-triumph-motorcycle.html |publisher=Motorcycle Magazine |access-date=6 October 2019}}</ref> As a replacement for the ageing [[Engineering:Triumph Tiger Cub|Triumph Tiger Cub]], the '''TR25W Trophy''' was introduced in 1968. (The "W" in the model designation stood for "woodsman"){{sfn|Turner|2017}} The machine shared the chassis of the Starfire, but used 19" wheels front and rear, with a steel Triumph tank and side panels, high bars and a high level exhaust on the right hand side. The TR25W was built at BSA's Small Heath factory.<ref name="Motorcycle Classics">{{cite web |title=Beezer Behind the Badge: 1968-1970 Triumph Trophy 250 - Classic British Motorcycles |url=https://www.motorcycleclassics.com/classic-british-motorcycles/classic-triumph-motorcycles/triumph-trophy-250-zmmz17jazhur |website=Motorcycle Classics |access-date=6 October 2019 |language=en |date=July 2017}}</ref>

A steel fuel tank was used for all years and in 1969 and the machine also received the 7" tls brake. The exhaust was moved to the left side for 1970.<ref name="Motorcycle Classics" />

===T25T Trail Blazer===

The '''T25T Trail Blazer''' was virtually identical to the BSA ''Victor Trail 250'' apart from paint finishes and badges.{{sfn|Jones|2014|pp=65-67}}

===T25SS Trail Blazer SS===
The '''T25SS Trail Blazer SS''' was also known as the '''Blazer SS'''.{{sfn|Brooke|Gaylin|2017|p=158}} It had a slightly different tank to the BSA ''Gold Star 250'', but otherwise was the same except for paint finishes and badge. A {{convert|3|impgal|USgal}} tank was available, which because of its extra length required a shorter dualseat to be fitted.{{sfn|Jones|2014|pp=65-67}}

==References==
{{reflist}}

===Bibliography===
* {{cite book |last1=Brooke |first1=Lindsay |last2=Gaylin |first2=David |title=Triumph Motorcycles in America |date=2017 |publisher=Motorbooks |isbn=9780760359587 |url=https://books.google.com/books?id=H85EDwAAQBAJ&q=trail+blazer&pg=PA160 |language=en}}
* {{cite book |last1=Henshaw |first1=Peter |title=BSA 350, 441 & 500 Singles: Unit Construction Singles C15, B25, C25, B40, B44 & B50 1958-1973 |date=2015 |publisher=Veloce Publishing Ltd |isbn=9781845847562 |url=https://books.google.com/books?id=-tPBCQAAQBAJ&q=bsa+starfire |language=en}}
* {{cite book |last1=Jones |first1=Brad |title=BSA Motorcycles: - the final evolution |date=2014 |publisher=Veloce Publishing Ltd |isbn=9781845846473 |url=https://books.google.com/books?id=VhpNBAAAQBAJ&q=b25 |language=en}}
* {{cite book |last1=Reynolds |first1=Jim |title=Best of British bikes |date=1990 |publisher=Patrick Stephens |isbn=9781852600334 |language=en |url-access=registration |url=https://archive.org/details/bestofbritishbik0000reyn }}
* {{cite book |last1=Ratio |first1=Rupert |title=Rupert Ratio Unit Single Manual: Volume 3: Lesser known Models |date=2014 |publisher=Panther Publishing Limited |isbn=9781909213173 |language=en}}
* {{cite book |last1=Richmond |first1=Doug |title=Popular Mechanics |date=December 1967 |publisher=Hearst Magazines |chapter-url=https://books.google.com/books?id=zNMDAAAAMBAJ&q=bsa+starfire&pg=PA116 |language=en |chapter=PM Tests: BSA's 250-cc Starfire}}
* {{cite magazine |last= Savadori |first= Clement |date= October 2007 |title= Retrospective: BSA B25 Starfire 250: 1968-1970 |url= https://ridermagazine.com/2007/10/22/retrospective-bsa-b25-starfire-250-1968-1970/ |magazine= Rider }}
* {{cite magazine |last= Turner |first= Phil  |date= February 2017 |title= Reputation Ill-Deserved |url= https://www.classicmotorcycle.co.uk/reputation-ill-deserved/ |magazine= The Classic Motorcycle }}
* {{cite book |last1=Wright |first1=Owen |title=BSA: The Complete Story |date=1992 |publisher=Crowood Press |isbn=9781852237028 |language=en}}

==External links==


[[Category:Single-cylinder motorcycles]]

{{Sourceattribution|BSA B25}}