THUNDERBOLTS AND LIGHTNINGS
Peter Crawford’s new book takes an in-depth look at BSA’S ground-breaking unit-construction A65 and A50 twins
Mick Duckworth reviews a new book about BSA’S big unit twins
BSA MADE APPROXIMATELY 109,000 unit-construction heavyweight twins between 1961 and 1973. The 500cc A50 and 654cc A65 models from Birmingham were prime examples of British iron dominating those capacity classes in markets worldwide through the 1960s.
A choice for many dedicated motorcyclists and significant dollarearners, the grunty twins also enjoyed sporting success: two Production class victories at the prestigious Hutchinson 100 stand out; Mike Hailwood’s 1965 heroics at a wet Silverstone on an A65LC Lightning Clubman and John Cooper’s win with an A652S Spitfire MKII at Brands Hatch in the following year. The A65 engine dominated the national sidecar scene for several seasons and scooped a 1-2-3 victory in the inaugural 750cc Sidecar TT of 1968.
A book dealing exclusively with the big BSAS had been overdue until the publication of Thunderbolts & Lightning by Peter Crawford, a 280page hardback that is clearly the result of extensive research.
Taking its title from the two bestselling unit twins, it tells the yearby-year story of all the variants in great detail. The author interviewed many former non-management BSA
employees, who recount their involvement with design, development, testing and production. They include wellknown names like sidecar racers Chris Vincent, Norman Hanks, Nigel Rollason and Peter Brown, as well as a variety of relatively unsung figures from the drawing office to the test track. Their largely un-edited recollections take the reader inside the time-worn Small Heath factory and the BSA Group’s R&D centre at remote Umberslade Hall. There are also quotes from period owners and others with BSA links, along with views from deceased BSA managers garnered from credited sources.
Unlike most British classics, the A50 and A65 are not attributed to a single principal designer. Crawford surmises that Edward Turner, MD of BSA’S automotive sector, and his right-hand man Bert Hopwood at Bsa-owned Triumph, directed BSA chief designer Ernie Webster. Terry Gapper, one of the drawing office team that laid out the engines, recalls being given drawings of the existing 650cc pre-unit A10 engine for reference. The brief was to create a modernised unit-construction version of a twin that had done well for BSA since 1950. Like its predecessor, the new engine featured a single camshaft with pushrods inside the cylinder castings, but the 654cc A10 unit deviated from tradition in having a bore (75mm) slightly greater than the stroke. Chubby engine cases were accompanied by staid styling on the early 500cc and 650cc Stars.
The book follows development
from the tame-looking originals with negligible performance gain over the pre-units to the mechanically improved, more rugged and speedy Thunderbolts, Lightnings, Spitfires and Firebirds of the late 1960s.
As home sales declined, BSA focused on selling big bikes to North America, shipping 17,500 twins in 1967. But by 1971, when the A65s were re-styled (along with Triumph’s 650s) by Umberslade Hall, Honda’s CB750 four was mopping up in a US market that was peaking anyway.
The final fling before the demise of the BSA brand in 1973 was the Us-only 751cc A70, of which 203 were produced. Its development was bungled, mainly, according to the book, because managers ignored advice from staff, notably draughtsman Les Mason and factory-based sidecar racers, who were already running jumbo twins.
We learn that internal relations at BSA were far from harmonious. Mason had been among those who believed the A50/A65’S timing-side plain bush main bearing should have been replaced by a roller bearing, as it was on A50-based twins prepared for Daytona in 1966 and 1967. Leaving Small Heath in frustration, he marketed the Devimead bearing and crankshaft conversion, a descendant of which SRM offers today. A front disc brake on the cards in 1967 was allegedly quashed by Hopwood, while draughtsman Ed Wright left the company over blunders in developing the 1971 conical-hub front drum brake.
Other topics explored include the experimental dohc top-end, the 180° crankshaft prototype, the special Spitfire MKIV cylinder head that clinched a 14.07s standing quarter, mysterious Y-suffix engine numbers, the hated 1971 grey frame and the notorious ‘leakage’ of parts from the factory.
Self-published by Crawford under the Wideline imprint and priced at a reasonable £25, this substantial and informative book should be a hit with owners and fans of the BSA unit twins. For the more general reader, it offers graphic insight into how BSA aimed to be progressive but was increasingly hobbled by disorganisation and market conditions that ultimately led to the 1973 collapse. It will be followed by a second volume devoted to racing.