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• Auction House:
  Donington Auctions
• Sale Name:
  Collectors' Motorcycles, Cars & Horse Drawn Carriages - Featuring the Private Museum of Racing Driver Bryan Thomson
• Sale Date:
  20 Jun 2021 ~ 2pm (AEST)
• Lot #:
  36
• Lot Description:
  BSA 500CC A7/A10 - 'Eastern Suburbs Barn Find, 50+ years of ownership'
  Early A7 engine in a later A10 Plunger frame. Offered by the family of the Late Robert McLennan (50+ years of ownership)
• Notes:
  When Triumph released the Speed Twin in 1937, they threw the gauntlet to the rest of the British motorcycle industry and forced them to follow suit. Triumphs twin was immediately successful. It looked similar to the ubiquitous single, was faster and lighter, and only slightly more expensive. As Triumphs main competitor, BSA wasted no time in developing their twin, and they had a development machine running by 1939. War intervened and the first production BSA twin, the 500cc A7 appeared late in 1946. Like many British designs, the A7 had its roots in an earlier design, in this case Val Pages Triumph Model 6/1 of 1933. The 360-degree twin included a single gear-driven camshaft at the rear of the crankcase operating all four pushrods and a four-speed gearbox was bolted in semi-unit form to the rear. The first A7 was known at BSA as "Mr Perkins baby", after the designer Howard Perkins. With a cast-iron barrel and cylinder this was a long stroke design, the dimensions of 62x82mm providing 495cc. Allowing easy serviceability, the A7 featured a forged one-piece crankshaft with bolted-on flywheel, a gear-driven magneto behind the engine, and a chain-driven dynamo mounted at the front. The cylinder head was a one-piece cast-iron casting, designed with large openings between the cylinders and two separate wells for the pairs of inlet and exhaust valves separated by a lateral air space. With a single Amal Type 276 carburettor the A7 produced 26 horsepower at 6,000 rpm. The rest of the machine was fairly orthodox for the time, with a duplex frame, 19-inch wheels front and rear, 7-inch single leading shoe brakes, and 6-volt Lucas electrics. Early versions had a rigid rear end, with a plunger rear suspension option available from 1949. With a plunger the dry weight was 180kg but the A7 could be punted along quite briskly along the empty back roads of the late 1940s and early 1950s. Determined to take on Triumphs new 650 Thunderbird, in 1948 BSA lured Bert Hopwood from Norton to redesign the A7. This was primarily to allow an increase in capacity to 650cc but Hopwood also sought to cure the combustion problems of the earlier design. A shorter stroke permitted the engine to rev more freely, and a larger bore, allied to a slight downdraft angle from the single carburettor, offered more efficient cylinder filling and combustion. The basic 650cc A10 was the Golden Flash and this new engine was installed in the existing plunger A7 chassis. Painted golden beige the Golden Flash was tremendously popular and soon earned a reputation for outstanding durability. For 1953 the A7/A10 gained a fashionable headlight cowling and new taillight and in 1954 swingarm rear suspension was optional. Although overshadowed by Triumph, in the eyes of many the A7/A10 was the quintessential post-war British twin. The BSA A7 twin on offer here combines a 1948 first series A7 engine in a 1953 A10 Golden Flash plunger frame. The engine is standard, still with a single Amal carburettor and the standard exhaust system. The chassis includes a 1953 A10 Golden Flash plunger frame, with the updated headlight cowling and taillight. The colours are not standard but the motorcycle is otherwise very original. Last registered in Victoria in 1984 it is sold unregistered.
• Estimate:
  A$11,000 - 15,000
• Realised Price:
  $0.00
• Category:
  Automobiles & Accessories

This Sale has been held and this item is no longer available. Details are provided for information purposes only.