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British Motorcycles

 

Bradshaw Oil-Cooled Engines


Bradshaw y sus motores refrigerados por aceite

El sistema SACS (Suzuki Advanced Cooling System) fue desarrollado por Suzuki a principios de los 80s y utilizado a partir de 1985 en muchos de sus modelos. Sin embargo esto no es una novedad, ya que mas de 65 años antes lo utilizaron varias motos inglesas.

Granville Bradshaw, para muchos un genio imperfecto, fue un ingeniero de ideas particularmente avanzadas, responsable entre otras muchas cosas de las motocicletas ABC bicilíndrica transversal (luego imitado por BMW), la Panthette V-twin transversal y los motores de válvulas a la cabeza refrigerados por aceite Bradshaw. Sus diseños recibieron el respeto universal debido a su original enfoque, pero se decía que requerían una atención especializada para mantenerlos en funcionamiento, y pocas veces fueron comercialmente competitivos.

Con el objetivo de mejorar la eficiencia de los motores a altas temperaturas de trabajo sin sobrecalentamiento, Bradshaw patentó a principios de los años 20 un motor refrigerado por aceite que pronto fue utilizado por mas de 40 fabricantes de motocicletas. Inicialmente, en 1921, Zenith comercializó los Modelo A y B con una versión Bradshaw 494cc flat-twin y transmisión Gradua. Posteriormente, durante toda la década del 20, otras marcas usaron el mas conocido monocilíndrico de carrera larga de 348 cc (68 x 96 mm), entre ellas OK Supreme, Montgomery, Cedos, Omega, Matador, Coulson, New Scale, New Henley, Connaught, Sheffield Henderson, Sparkbrook , DOT, Orbit, PV y Coventry Mascot. Una versión de 1100cc V-twin version fue adoptada por el auto ligero Belsize.

El cilindro del motor Bradshaw estaba integrado con el cárter y contenía una camisa de hierro que lo rodeaba. Al igual que los motores refrigerados por agua, estaba desprovisto de aletas, aunque si usaba aletas para refrigerar por aire la tapa de cilindro de hierro. El aceite del motor, almacenado en un cárter húmedo, se bombeaba a la biela de donde salpicaba para arriba la camisa del cilindro.
Si bien fueron apodados como los "hervidores de aceite" porque se decía que tendían a sobrecalentar cuando se los exigía, no hay evidencias concretas que esto fuera así.


Suzuki developed oil-cooled engines in the 1980s which proved highly successful but innovative it was not as a similar system was used in British engines of the 1920s built by the Bradshaw company.

Granville Bradshaw was a brilliant and innovative engineer whose career spanned the formative years of the automotive and aviation industries. His motorcycle designs have passed the test of time with his horizontally opposed twin designs being adopted by Douglas, BMW and numerous others. These ABC aviation engines were fitted to motorcycles built by Sopwith in 1918 and by the equally famous French aircraft engine manufacturer, Gnome-Rhone. Another of his designs is the V-twin Panthette engine built by Phelon & Moore in the mid 1920s which looks for all the world like Moto Guzzi's granddaddy. Panther's Sloper, which remained in production for some 25 years, was also a Bradshaw design.

HO Twin

Horizontally Opposed Twin

Examples include BMW, Zundapp and Douglas HO Twins have conrods running on a common crank, with one on the exhaust stroke and the other on inlet.

Bradshaw's designs and patents were many and were widely admired, but commercial success was rare. In some ways he was like A.M. Low, another brilliant motorcycle engineer involved in aviation. It seems likely that they knew each other as Low's drones were powered by Granville's engines. If so, their friendship may have been strained after two aircraft crashed during testing in March of 1917, both due to engine failure ². The project was abandonded.

With the aim of improving the efficiency of his engines and reducing overheating, a problem encountered by a good many machines of the day, in the early 1920s Bradshaw patented an oil-cooled engine that in fairly short order was in use by more than 40 motorcycle manufacturers. One of the first was Zenith who in 1921 introduced models powered by the Bradshaw 494 cc flat twin. Subsequently, throughout the 1920 s, many other brands used the single cylinder 348cc (68 x 96 mm) oil-cooled engine. See below.

The  Bradshaw's unfinned cylinder was surrounded by a sleeve which retained the oil and was integrated with the sump. The oil is pumped to the connecting rod which splashed it onto the cylinder wall.

They were nicknamed "oil boilers" as it was said they tended to overheat at times, however there's no concrete evidence that this was so. Many motorcycles received nicknames, often derogatory; Royal Oilfield and Basket Stopped Again being classic examples.

The 1921-1924 Belsize-Bradshaw was fitted with a Dorman-built Bradshaw 1294cc oil-cooled V-twin which gained a reputation for being unreliable. (Wikipedia)


Marques employing Bradshaw oil-cooled engines:


Notes

1. The Suzuki Advanced Cooling System (SACS) was developed by Suzuki at the beginning of the 1980s and was in use from 1985 to the present. Suzuki reverted to watercooling on the GSXR in 1992, but SACS remains in use on their Bandit/Katana and DR off-road series at time of writing (2016).

2. "In March 1917 two test flights were conducted at the Royal Flying Corps training school. Both vehicles crashed due to engine failure." ~ The V2 and the German, Russian and American Rocket Program, by Claus Reuter.

Sources:



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