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BSA’s Bonneville Beater

June 1, 2013
BSA A65 Spitfire

Story and photos by Graham Clayton

By 1965, Triumph’s T120 Bonneville (reputedly good for 120 mph) was generally accepted as the top sports bike for fast street riders. Other manufacturers had responded with their own super sports road burners, such as the Norton 650 SS and Manxman, and the BSA A65 Lightning, but the Bonneville was still viewed as the must-have bike by most of the “go fast” crowd.

Enter the 1966 Spitfire Mk II, BSA’s “Bonneville beater,” an up-rated A65 model designed with production racing in mind, and meant to challenge the Triumph T120’s top streetbike claim.
BSA had originally introduced the A65 series of OHV vertical-twins in 1962. Unlike earlier BSA 650s, the A65 had an over-square bore and stroke with a displacement of 654 cc. It was also of unit-construction design, with oval-shaped, polished crankcase covers that gave what was called the “power egg” look, popular with many engine designers at that time, but most notably the Italians.

BSA A65 Spitfire The Spitfire engine came in a high state of tune that yielded 54 hp, thanks to the use of 10.5:1 high-compression pistons, hotter cams and a pair of Amal 1-5/32” GP2 carbs that shared a matchbox-type racing float chamber and were fitted with unscreened, aluminum velocity stacks. This was several more horsepower than what a typical T120 produced, and delivered strong acceleration.

A triplex primary chain connected the crankshaft to a wet clutch, and a close-ratio, four-speed gearbox used tall third and fourth gears, spaced fairly close together to facilitate fast, spirited riding while yielding a top speed of around 115 mph (185 km/h).

The A65 engine had a forged, one-piece crankshaft with a central flywheel. The cam was located in the lower crankcase, above and behind the crankshaft at the base of the barrel, and it operated pushrods that were located in a tunnel through the centre of the crankcase. The cylinder barrel was a one-piece, iron unit mated to a single, twin-port aluminum head. This gave the engine a clean look, free of the many cables, oil lines and linkages associated with many motorcycle engines of the day. It looked new and modern.

The Spitfire engine was bolted into a black, new-for-1966, steel-tube frame with a large-diameter, single-backbone tube connected to twin down-tubes front and back to form a full cradle layout. A welded subframe provided support for the dual race-humped saddle, swingarm, rear suspension and fender. The low-slung exhaust used dual tube-shaped mufflers. Both centre and side stands came standard.

The Spitfire suspension consisted of a pair of black telescopic forks and gators and a swingarm fitted with twin, fully enclosed Girling shocks, new for 1966. The suspension was compliant enough for around-town riding, while suitably firm for fast roadwork.

The Spitfires rolled on 19-inch front and 18-inch rear rims laced onto hubs that housed a pair of single-leading, twin-shoe drum brakes. The front brake was a 190 mm unit with five heat-venting holes machined into its left-side cover, while the rear was a conventional BSA seven-inch unit. Chromed, sport-type fenders were used both front and back. Tires were typically Dunlops.

Three different fuel tanks were made available between the home-market and U.S. export models, including a standard, four-gallon (18 litre) fibreglass sport tank for the home market, plus an optional five-gallon (22.7 litre) competition-type fibreglass fuel tank for production racing, and for road-bike use in 1967. For the U.S. market, a 1.9-gallon (8.5 litre) peanut-type tank was made standard; this tank style became popular after its introduction on the 1957 Harley-Davidson Sportster. All gas tanks were rubber mounted…

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