Introduced in 1932 and built for only that season, the BS4 reflected George Brough's desire to build a machine that offered both exceptional performance and unparalleled refinement. In order to meet the latter criteria water cooling was considered necessary leading him to look at existing automotive engines as a possible power source, with his eye eventually settling on the lightweight four cylinder unit produced by Austin for the ubiquitous "7". Negotiations were started with Herbert Austin to secure a supply of the engines, taken out to their maximum bore to give a displacement of 800cc and fitted with an alloy cylinder head and water pump to save weight.
In order to utilise the Austin gearbox and transmission Brough opted to employ two rear wheels with the shaft drive, rear fork and final drive housing between them. This arrangement ensured that the weight of the power train remained central to the machine. Castle forks were employed at the front and two linked radiators were mounted on either side of the front down tube, effectively serving as legshields.
Finished to the usual exceptional standard ten examples were built during 1932, with the last one sold in 1934. Although primarily considered to be a sidecar machine they were also used as a solo mount.
In 2016 a fairly rugged example of the BS4, one of the "Broughs of Bodmin Moor" ( perhaps the greatest barn-find of all time) sold at auction for almost half a million US dollars.
The Daily Mail claimed that it may sell for three million pounds, despite Bonham's estimate of between $110,000 and $170,000. Hard to imagine why the Daily Mail is banned by Wikipedia.
Sources: H&H Classic Auctions, Bonhams, The Daily Mail, et al.
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