New Rules: 1971 BSA A70L 750 Lightning

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!

The result was a compact engine that resolved two issues Hopwood disliked about the Triumph twin. First, the train of five gears driving the camshafts and magdyno meant the engine was always going to be “a rattler.” Second, Hopwood believed Triumph’s use of external pushrod tubes compromised airflow over the cylinders. So his BSA twin used a single camshaft at the rear of the engine, driven by two gears with chain drive to the magdyno, with the pushrods running inside the cylinder block.

During its 14-year run, the long-stroke (70mm x 84mm) A10 650cc engine was updated with larger big end bearings and an alloy cylinder head, and begat sports versions like the Super Flash, Road Rocket and Super Rocket. A redesign in 1963 incorporated the transmission into the engine cases, and the new “power egg” BSA twins were born. The new A65 engine boasted over-square dimensions of 75mm x 74mm, which allowed it to produce more power at higher revs. That gave rise to two issues: excessive vibration when the revs were used; and a tendency for high wear rates in the timing side crankshaft bush, leading to loss of oil pressure — and an engine blowup.

In 1971, the aging engine was shoehorned into the new oil-in-frame P39 chassis shared with Triumph, and treated to new cycle parts. Among these were new Slimline forks, a twin-leading-shoe drum brake and a squared-off gas tank. The new frame was ridiculously tall, requiring a 34-inch inseam just to tippy-toe around. This was alleviated over the course of 1971 along with several other improvements, including wider flanges on the engine cases to reduce oil leaks and a higher capacity oil pump.

The A70 Lightning

The 1971 BSA A70L was externally identical to the production A65L of the same year. Only the telltale “750” decal on the side panels (and the engine number stamp) was different. Inside, the main change was a new crankshaft giving an 85mm stroke, with new rods to suit the longer crankshaft throws and new pistons giving 9.5:1 compression versus the 650’s 9:1 ratio. Carbs were still Amal 930 Concentric, but with a larger 250 main jet. BSA listed the crankcases as being new, though it’s not clear what the differences were from the A65L, apart from a change to accommodate a different timing side crankshaft bush.

Just 202 A70Ls were produced: 65 in June; 101 in July; and 36 in August of 1971. Estimates are that around 180 were shipped to BSA East Coast in Baltimore, with the remainder going to California. The majority of the bikes had the 1972 black-painted frame, though at least one is known to have been finished in the ivory 1971 paint finish. Although they were presented as 1972 models, they were all stamped for 1971.

It seems at least some of the A70s were dispersed around to a number of U.S. dealers, though many were also stripped of their engines, which ended up in flat-trackers. Unfortunately for BSA, the day of OHV parallel twins on the track was almost over. The A70 was never listed in BSA sales literature, and there’s no indication it would have replaced the A65 in the BSA model lineup. In fact, the BSA sales brochure for 1972 listed just four models: the B50SS “Gold Star;” the A65L Lightning and A65T Thunderbolt; and the A75RV Rocket 3.

In any case, events caught up with BSA during the following months as Barclays bank, now effectively running the company and trying to stop the financial hemorrhaging, slashed production. From August to October 1971, BSA produced 6,286 machines; from November 1971 to January 1972, 785; and from February 1 to April 14 (when production at Small Heath stopped completely) just 202 bikes were built. In just 14 months BSA had gone from winning Daytona to dissolution.

George Wood’s BSA A70L 750 Lightning

One of the ones that got away belongs to George Wood of Port Orchard, Wash., a small community on Washington’s Olympic Peninsula, just across Puget Sound from Seattle. A committed British bike rider and BSA fan, George bought his A70 new in 1971 from Gonzalez Motors in Tacoma, Wash.

“I had a 650 Hornet, and I was hanging out in the local BSA dealer’s shop,” George says. “This A70L was on the floor. He got it out of California and his mechanic was going to buy it. That fell through, and I was there drooling over it, so we struck a deal. I can’t remember now if it was $2,500 or $2,800 for that bike, but it was a lot of money back then.”

Owned from new, it was also ridden regularly. “I used it to commute back and forth from Tacoma to Seattle between 1971 and 1978, so I put on some fairly hefty miles. I forget now how many miles I had on it, but every day I rode that bike, it was a real trooper. It was reliable, and I learned a lot about BSAs,” George says. “In 1978 I was out riding around and got hit by another vehicle. That smacked up the left side pretty bad, and I was injured a little bit, too. So it got put in the back of the garage and it’s sat there many years. I’ve moved three times since.”

It was a year ago or so when George decided it was time to restore the BSA A70L. By that time, he had acquired two more British bikes, both triples (a Triumph Trident and a BSA Rocket 3), and he decided to enlist the help of his brother in Idaho Falls, Idaho.

“My brother found a really good mechanic in Idaho Falls. I took all three bikes down there, parked them at my brother’s, took the Trident over to Brian St. John [of Legend Cycle], and told him to get it running and see what we can do,” George says.

“A fellow came in and made an offer on the Trident, and that allowed me to fix up the other two bikes. I had the A75 fixed up and that’s what I’m riding now. The A70L restoration took about a year. I had most of the parts that I’d gathered up over the years. But there was a lot of little stuff I needed to find. The tough one was the tachometer and speedometer. Somehow I’d misplaced them in the moves, and it was tough finding those.”

With the Lightning back together, George can reflect on what it meant to own one back in the day and what it means to own one as a collectible classic today. “Back in 1971, they weren’t the quality of motorcycle you can buy now. Things would vibrate loose. One day I was riding down the freeway and the petcock vibrated loose from the gas tank, so that was pretty exciting! Apart from that it was just flat tires, broken spokes, misalignment. Things like that just happen. I think all those BSAs vibrate pretty good. Back then we didn’t know any better.”

So could the A70L have been a contender as a new full production BSA? “It was really the last gasp,” George says, “and every time I read about it, 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 on the superbike craze that came on. I think they pretty much shot themselves in the foot. The A75 came out and the Honda came out about six months later. You never heard about the BSA after that,” George says.

“The 1967 Hornet that I had really got me hooked on them,” George continues. “I wish I’d kept that too, but you can’t keep everything. I had a Victor and the Hornet, and right now I’m looking for a little single I can potter around on. The BSA A70L 750 Lightning has just a little too much power for the residential area I live in now. You can get up to 55mph real quick and I don’t want to get another ticket!”  MC

Read about how rare and collectible the BSA A70L Lightning is in Low Numbers, High Collectability: The BSA A70L 750 Lightning.