New Rules: 1971 BSA A70L 750 Lightning

A last gasp model from a dying motorcycle manufacturer, the BSA A70L 750 Lightning was too little, too late.


| November/December 2012



BSA A70L

AMA Class C rules required competing machines to be based on production bikes, meaning that BSA would have to produce at least 200 750cc twins to homologate their new racing machine for competition use. The A70L 750 Lightning was the result.

Photo By Stephen Clark

1971 BSA A70L Lightning 
Claimed power: 52hp @ 6,250rpm (est.)
Top speed: 120mph (est.)
Engine: 751cc air-cooled OHV parallel twin, 75mm x 85mm bore and stroke, 9.5:1 compression ratio
Weight (dry): 390lb (177kg)
Fuel capacity/MPG: 3gal (11.3ltr)
Price then/now: $2,500 (est.)/$4,000-$8,000

In 1971, the BSA/Triumph Group was effectively bankrupt. Through a period marked by astonishing ineptitude, the company, once the largest motorcycle manufacturer in the world, lost its foothold in the only significant market it had left: the United States.

Yet that same year they fielded a factory team of 10 riders (including Dick Mann, Don Emde, Dave Aldana, Gene Romero, Gary Nixon, Mike Hailwood and Paul Smart!) on BSA and Triumph-badged 750cc triples in order to wrestle the Daytona 200 mile title from Honda. Dick Mann won that race for BSA (as he had for Honda the year before) and went on to take the Grand National Championship in the first ever “Grand Slam,” winning every race in the series. What does this have to do with the 1971 BSA A70L 750 Lightning, an extremely rare model you’ve likely never seen or even heard of? Quite a lot, as it turns out.

The BSA A70L

Until 1969, British motorcycles competing in AMA events were restricted by the AMA’s 1933 (amended in 1954) Class C equivalency formula, which required overhead valve engines to be less than 500cc with a compression ratio of less than 7.5:1. (Flathead engines were allowed up to 750cc.) With the increasing influence of import motorcycle sales in the late 1960s, the AMA was forced to relax its rules to include all 750cc production-based bikes — just in time for Harley-Davidson to replace its aging KR flathead race bikes with the new Sportster-based XR750.While the 750cc Rocket Three triple produced plenty of power, it was a large, heavy engine. It was also the only 750 that BSA built. And though AMA Grand National racer Jim Rice enjoyed success with his Trackmaster-framed triple, BSA recognized that a lighter 750cc twin might fare better in Grand National flat track races.

However, AMA Class C rules required competing machines to be based on production bikes. That meant BSA would have to produce at least 200 750cc twins to homologate the machine for competition use. The A70L 750 Lightning was the result.

Prologue

The basic layout of the A70 engine can be traced back to Bert Hopwood’s A10 650 twin of 1949. BSA and Triumph were fierce competitors then — BSA didn’t buy Triumph until 1951 — so when BSA’s brass heard that Triumph would introduce a 650 in 1949 (the Thunderbird), they charged Chief Designer Bert Hopwood with creating one for BSA. This Hopwood did — in four weeks!

DAVID PATTERSON
12/23/2012 6:02:44 AM

"I get kind of mad at the management, because they could have brought the A75 Rocket 3 out two or three years sooner and beat Honda to the punch." Sorry George, but it was BSA's insistence on its own version which delayed the debut of the Trident. If Doug Hele had had his way, we'd have seen triples in '66 from Triumph. How BSA could own Triumph and not learn anything about proper bearings and crank oiling is beyond me. Then, to sabotage the possible success of Triumph's new model by playing, 'me too.' The company deserved to die.






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