▲ Above: Rare BSA A70L Lightning. This 750cc "homologation special" fetched $12,650 (inclusive of buyers premium) at Bonhams' January 2013 Bally's Las Vegas Hotel & Casino Sale, more than double the price of its smaller 650cc stablemate, the BSA A65 Lightning.
1971 BSA A70L specifications
BSA A70L Lightning frame and fork
BSA A70L Lightning brakes, wheels & tyres
BSA A70L electrics
BSA A70L colours
Riding the BSA A70L
BSA A70L Lightning specialists and links
Genuine BEEZA GEEZA
£12.99 plus P&P
Type: Air-cooled, OHV parallel twin
Capacity: 751cc (750cc)
Bore & Stroke: 75mm x 85mm
BHP: 54 @ 7000rpm (estimated)
Compression ratio: 9.5:1
Transmission: 4-speed, multi-plate
Brakes: 8-inch drums (TLS) front, and 7-inch (SLS) rear drum
Electrics: 12-volt, 180W alternator, twin coil
Front suspension: Telescopic, two-way damped
Rear suspension: Twin shocks/dampers with pre-load adjustment
Wheels: 18-inch x 3.25 inch front, 18-inch x 4.00 rear
Weight: 390lbs (dry)
Maximum speed: 110mph
Burton Bike Bits
PO Box 7691
Ashby de la Zouch
BSA UK Owners Club
Unit 22, Glanyrafon Enterprise Park
Ariel and BSA specialists. Hugely knowledgeable. Remanufactured and hard to get spares.
IT'S THE LARGEST CAPACITY BSA TWIN that Small Heath ever built, and one of the rarest. The 750cc A70L first appeared in 1971. Two hundred examples were manufactured to satisfy the homologation requirements of the American Motorcyclist Association (AMA).
Some sources claim that just one extra bike was built (as the biking equivalent of a baker's dozen). And some say the true number was actually two extra machines. Either way, everyone is agreed that at least 200 units were built and shipped out of the factory gate intended for the US east and west coasts (with, according to rumour, a few going out under the counter to UK customers).
The A70, aka A75L—L for Lightning—is essentially a run-of-the-mill, nothing-to-get-overly-excited-about circa 1971/1972 BSA A65, albeit with a longer stroking engine providing a bore and stroke of 75mm x 85mm as opposed to the A65's 650cc 75mm x 74mm over-square lump.
The compression ratio for the OHV, air-cooled, 360-degree A70 was raised from the A65's 9:1 to 9.5:1, and various internals were correspondingly reworked to deal with the extra power.
Pistons are unique to the bike with taller domes and lower-set gudgeon pins. The crank, naturally enough for a longer stroke A65 variant, has a greater throw and is supported on the drive side by a standard A65 roller bearing, and a slightly narrower plain bush on the timing side (1/4-inch narrower, actually). SRM Engineering in Wales, incidentally, offer what they claim is a significant upgrade for the main bearings of BSA twins of this era which provide better support, improved crank location coupled with increased oil flow.
BSA also upgraded the oil pump from the A65's alloy type to an iron-bodied unit.
The 750cc A70s were built and sold with twin 30mm Amal carburettors, while the 650cc A65 was available as a single-carb Thunderbolt, or the twin-carb Lightning (both also 30mm). The nearest Triumph equivalent to these last two bikes is actually the short-stroke TR65 Thunderbird that appeared in 1981.
The A70 clutch, as fitted to the A65s, is a three-spring, multi-plate Triumph unit with integral shock-sbsorber; not the greatest in the world, but generally competent and better than just about anything that Small Heath ever built.
The gearbox is four-speed. The primary chain is triplex.
The steel, all-welded, twin-cradle oil-in-frame rolling chassis is the same as that fitted to the A65 Lightning, the late Triumph T120, and the Triumph T140 (all models).
Designed at Umberslade Hall (BSA's contentious design department in Warwickshire, UK), this equally contentious frame suffered numerous problems when introduced by the firm, notably by developing cracks around the centre stand and swinging arm lugs. And although the factory subsequently redressed the problems, the bad reputation lingers on, and potential buyers are often deterred from purchase.
Another criticism of the original oil-in-frame chassis was that it was overly tall and suited only "six-footers".
Later frames were reworked and lowered (both for Triumph and BSA machines), thereby bringing the seat height down to around 31/32 inches.
In its day, where many riders had moved up (literally) from low sprung saddles and pint-sized British singles, every one of those inches was felt. But by modern standards, it's just no big deal for the vast majority of riders.
The never-more-than-adequate two-way damped front fork is standard A65 fare. Ditto for the rear shocks which are adjustable only for pre-load. If you're above average weight, you might want to look at getting something a little stiffer at both ends, perhaps with adjustable damping settings at the rear. And if you're below average weight, you might want to try something else anyway to keep the rear end in check on tight bends, especially where those bends also throw in a few bumps and/or ripples.
These machines tend towards skittishness. But modern Hagon shocks are perfectly acceptable and tend to last well.
The front brake is an 8-inch twin-leading shoe conical hub. The rear is a single-leading-shoe 7-incher. Both are merely okay, but only as long as the owner/keeper maintains them properly and sets them up right. In fact, in wet-weather, you'll probably be glad of them.
Some riders dislike this brake set-up, but we've never had much trouble with it, as long as its otherwise in good condition. But if you're riding hard and fast, notably in a hot climate, you'll experience some fade if you're not careful. Except that few, if any, A70 owners are going to be giving their bike a sound thrashing anymore. These machines have become too expensive and too rare for their own good, and most will be paraded or enjoyed at less dramatic velocities. So if you want to seriously use and even abuse an oil-in-frame BSA twin, you can pick up an A65 for less than half the price.
The wheels/tyres are 3.25 x 18-inch front, and 4.00 x 18-inch rear. The wheelbase is 56-inches, and ground clearance is around 7-inches. Scraping the pegs is fairly easily, and you can even get a few sparks off the megaphone silencers if you try really hard.
T140 parallels continue with the feel of the bike on the move. The revs don't pick up as quickly as the shorter-stroke 650cc A65s, but the A70 certainly throws out more torque and lopes along more confidently in the mid-range. And yes, it also vibrates pretty much like a T140, which means that you won't want to spend much of your life galloping along at anything much above 70-80mph for sustained periods.
The crankshafts were always statically balanced by the factory, which was fine up to a point. But dynamic balancing is the way to go and can make a huge difference to the feel, thereby liberating otherwise "trapped" performance.
BSA's engineers no doubt knew that for general road use they'd pushed the design beyond its reasonable limits. As with Triumph, BSA parallel twins were wonderful as 500s, acceptable as 650s, and marginal as 750s. But they'll carry you in solo or two-up comfort forever if you can live with their foibles, and maintenance is, mercifully, easy.
Many of the engines from the original homologation batch were removed for racing, incidentally (and no one cared too much about the vibes on the US short stroke circuits). Engines were also cannibalised by other racers, and many more bikes have since donated limbs and organs to other dying recipients.
The AMA approved the bike's suitability on September 11th 1971.
Most of the surviving A70s are probably still Stateside. But they do still turn up in the UK and mainland Europe, and occasionally elsewhere in the world. Burton Bike Bits (see contact details on the left of this feature) own a prime example and have opened an A70 register. So if you own one, get in touch.
All the A70s were built in 1971, by the way, but many (if not most) are registered as 1972 machines.
The charging system is a 180-watt single-phase alternator feeding the juice to a 12-volt battery. The switchgear is marginal and doesn't like rain, or even damp air, and the standard wiring loom is easily capable of developing odd quirks and shorts. Expect to blow a few bulbs too. But at the same time, you can run for years on these electrics and never have a problem.
The colours for the A70 (main image) is a black frame, Etruscan Bronze & white fuel tank, with Etruscan Bronze side panels. Apparently, fluorescent stripes were also fitted to tanks and follow the horizontal key lines. Why this happened isn't clear, but it's likely that the US market demanded it, so BSA fitted them—never mind that side reflectors were also mandated and fitted to the bikes. Burton Bike Bits advises us that there is a part number for these stripes.
The A65 Lightning was finished in Firebird Red for the tank and side panels. The A65 Thunderbolt (see brochure image insert, above), was finished in Etruscan Bronze, also for the tank and side panels. Frames for both machines were primarily black, but there were also a Dove Grey frame option that's becoming increasingly sought after today.
Above: BSA 750cc A65 brochure image. Same rolling chassis as the 750cc A70, but packing a slightly smaller punch.
▲ Back to the top