Is the unit-construction oil-in-frame twin BSA’S poor relation? We find out...
BSA’S oil-bearing frame for its twin-cylinder range divides opinion among Small Heath faithful. Is it the last straw or a step in the right direction? We ride a ’71 Thunderbolt to find out...
As if the switch to unit-construction engines for BSA’S 500 and 650 twins for 1962 hadn’t irritated traditional BSA diehards enough, along came the new, oil-bearing frame for the A65 in 1971 to stoke their ire still further. ‘It’s too tall, it’s ugly, it’s not a proper BSA...’ they cried. And plenty bought into the naysayers’ narrative. The new model never sold as well as the ‘old’ A65 – particularly in the all-important American market. But is the oil-in-frame A65 really the aberration that a sector of the Small Heath faithful would have you believe?
To find out, I’m down at Anthony Godin’s showroom in Mereworth, Kent looking forward to putting a few miles on a restored 1971 Thunderbolt. The bike is a restored – though not 100% original – machine that Anthony acquired from a local BSA collector. Originally a non-uk bike, he believes it was originally supplied to the Iranian police. It’s finished in non-standard blue paintwork and is still at the running-in stage, following its restoration in 2019.
First impressions are good; I reckon the A65 is a handsome
machine. BSA’S unit-construction ‘power-egg’ engine is neat and uncluttered, while the Ceriani-lookalike forks and twin-leading-shoe front brake look right on style for the unit A65’s launch year of 1971. The all-welded frame looks neat and businesslike and I like the slightly boxy tank and wide, raised ’bars. There’s a hint of Stateside style about the bike that marks it apart from the very traditional-looking A65 model it replaced. So I’m convinced by the styling... but what about the ride?
Let’s get one thing out of the way for a start. I’m no giant at 5ft 11in, but I have to say I don’t have an issue with the seat height of the oil-in-frame A65. BSA quoted the seat height at 32½in, which is only ½in more than a contemporary Honda CB750 – or the previous year’s A65. The frame rails for the rear subframe are spaced quite widely at the front, forcing my legs out into the breeze a little once on the move, but starting the bike is easy enough without standing on tiptoe, as is manoeuvring it about on the forecourt. Certainly the seat height wouldn’t put me off owning a ’71 Thunderbolt – or any of the oil-in-frame BSA or Triumph models.
The handling wouldn’t, either. The Avon Speedmasters – a ribbed front and slightly square rear – aren’t the sportiest of rubber, but the bike tracks true on fast sweepers and feels equally at home tackling some of the twistier back roads the Kentish Weald can offer. The ‘four-stud’ forks are a definite improvement on the double-damped BSA forks on the 1970 models, too. If the 35mm units don’t quite have the action of the Cerianis they were clearly inspired by, then the difference is too small to notice. They’ll do for me.
Arguably, by 1971 the venerable unit-construction engine was the part of the A65 that most needed a radical update. Sure, the switch to unit construction back in 1962 was a step in the right direction but, by 1971 maybe a little more was needed to stay in the hunt. Honda’s CB750 had been on the market for a couple of years by then, bringing four cylinders, overhead cams, a five-speed gearbox and electric start to the masses. And even Yamaha’s new XS-1 twin – perhaps more of a direct competitor to the BSA – had an overhead-cam engine, five speeds and an electric boot. On paper, it was a mismatch. There’s no doubt the A65 was behind the Japanese in terms of technology and sophistication, but on the road things weren’t quite so clear cut. A modest 46bhp, a top end of around 105mph and a four-speed gearbox surely wasn’t the recipe for success in the brave new world of the ’70s. But the Thunderbolt manages to punch way above its weight on the road. The engine isn’t perfectly smooth – I well aware I’m aboard a big parallel twin – but that’s part of the raw allure of British iron. The BSA thunders up to the legal limit on a rorty
‘THE BSA THUNDERS UP TO THE LEGAL LIMIT ON A RORTY WAVE OF TORQUE AND THERE’S NO NEED TO GET INTO THE SERIOUS VIBRATION ZONE THAT LIES ABOVE 5500rpm’
wave of torque and there’s no need to get into the serious vibration zone above 5500rpm. The gearbox action is light and positive – who needs five-speeds when you’ve got a broad spread of torque – and the clutch behaves impeccably. It might ‘just’ be a pushrod twin with a single carb, but the Thunderbolt engine delivers a punchy, satisfying ride.
If I have to pick faults, the Lucas switchgear isn’t the easiest or most intuitive to use, the seat catch looks like it should be on a garden gate and that vibration does get a little intrusive if I venture much above 5500rpm. With peak power arriving just below 7000rpm, that’s a few valuable bhp lost – significant if I was racing my mate on his XS-1 Yam back in the day.
In truth, though, that’s not what riding a classic is all about these days – and the A65 easily keeps up with modern traffic, doing everything I could reasonably ask of it. I’d have to say I like it. It goes well, sounds great, the handling is above average and even the much-derided conical front brake works pretty well on my ride. Above all, it’s fun. It looks, feels and sounds like a proper Brit twin – and all with a sprinkling of American-market attitude and swagger. There’s nothing wrong with that – either now or in 1971.
Of course, the A65 wasn’t without its faults. For years, there had been some measure of unease concerning the longevity of the plain-bush timing-side main bearing. While many owners have reported years of trouble-free use with the stock bush, if there’s any significant wear in the bush, oil pressure to the big-end drops – with calamitous results.
While replacing a worn bush with a new one is fine if you catch it before any damage is done, BSA twins specialists SRM (srmclassicbikes.com) have developed a highly regarded ball/roller main bearing conversion that replaces the bush and provides lubrication to the big-end through a feed in the end of the crank. Not only is the oil feed to the big-end greatly enhanced, but the combined needle roller/ball main bearing locates the crank positively and eliminates the need to shim the crank, too. It’s win/win and, while some may consider it overkill, it’s a proven ‘belt and braces’ cure for timing-side main bearing woes. It’s not cheap, but what price peace of mind?
Minor faults aside, though, if I’m won over by the styling of the 1971 A65 and more than happy with the ride, why didn’t BSA have a sales sensation on their hands? After all, the Umberslade Hall designers had done their best to make the 1971 Thunderbolt (and the twin-carb Lightnings) look very different to the traditional BSA twin. With the company already in financial difficulty, the pressure was on to come up with something that could be realistically touted as a new model, without incurring too much in the way of development costs. And, having spent time, money and effort on getting the Umberslade Hall design centre up and running, it was there to which BSA turned for the key point of difference between the 1970 models and the 1971 Thunderbolt and Lightnings – the new-for-1971 oil-bearing frame. The plan was to use essentially the same frame for BSA and Triumph 650s for 1971, with the P39 frame being the result. A modern, all-welded twin downtube, double-cradle affair, it was bang up to date for 1971. And, instead of a conventional oil tank, lubricant was carried in a massive, three-inch diameter main frame tube that ran from the
steering head, curving down to the swingarm pivot. It was the backbone – literally – of an immensely strong and stiff chassis that provided excellent handling, as well as a safe repository for around five pints of oil. The oil filler was at the rear of the fuel tank, under the front of the seat, with the drain bolt at the lower extremity of the main frame tube/oil tank down by the swingarm. Simple and effective.
The oil-bearing frame concept wasn’t a new one, even in 1971. The Rickman brothers had used it on their successful Métisse scramblers as early as 1962, while, over in the States, Trackmaster had also adopted oil-bearing frames for their bespoke flat-track chassis kits.
The initial design was the work of Triumph designer Brian Jones, when deployed to the new Bsa/triumph Group design facility at Umberslade Hall in 1969. Jones’ design was adopted by Dr Stefan Bauer (formerly Norton’s head of engineering), who was one of the top men at Umberslade Hall, and given the thumbs-up for production in both BSA and Triumph form on the 1971 range of 650 twins.
‘THE SEAT HEIGHT WOULDN’T PUT ME OFF OWNING A ’71 THUNDERBOLT... THE HANDLING WOULDN’T, EITHER’
Looking back, perhaps the oil-in-frame BSA twins were either not enough, or too much back in 1971. Not enough to drag an early ’60s revision of a late-’40s/’50s design into the ’70s for too many new riders, but too much of a change from what they knew and loved for what was still a sizable rump of dyed-in-the-wool BSA fans. But, by then, the writing was on the wall for BSA anyway. It would have taken more than an update of their 650 twin to arrest the terminal decline of a one-time motorcycling giant.
That’s a shame. Because the 1971 A65 is actually a pretty good motorcycle. Good enough to put a smile on your face in the increasingly strange days of the 2020s. Fast enough, reliable enough, practical enough. And I, for one, think it’s a pretty cool looking bike too. Maybe it’s time to unpack all you think you knew about oil-in-frame BSA twins, throw it away and take a look at the late A65 with an unbiased eye. You might just be surprised.