A10 and the ART OF MOTORCYCLE MODIFICATION
Jon Jolley has created a BSA A10 fit for the 21st century from the bike he’s owned for 40 years. We look at what went into it and take it out for a ride
Jon Jolley wasn’t looking for a BSA A10 when he passed his bike test back in 1980. “I was after something like a Honda CB400F or maybe a Suzuki GT500,” he smiles. “I’d already passed my car test, but I fancied a bike. But I saw this advertised in the local paper and thought it might be worth a look – even though it was old. When I went to see it, it was in pretty good shape, really. I was 20 at the time. It had twin Gold Star silencers on it, and when the owner blasted it down the road to show me how well it went, I couldn’t believe how good it sounded. That sound sold it to me, and I paid £350 for it.” Owning that A10 opened Jon’s eyes to a new world. “I rode it round for a few years with no problems,” he recalls. “I joined the BSA Owners Club branch in Cardiff, where I then lived. It was really active back then. And then Steve Mcfarland started SRM in the city, so if I did have any little niggles with the bike I’d take it there and Steve could always sort them out. He developed a big bush conversion for the main bearing – a forerunner of the SRM needleroller conversion – to cure the premature wear issue that affected some A10s. It involved pressing a hardened steel collar onto the end of the crank and machining a larger diameter bush, pressed into the crankcase, to accept it. I had the conversion done on my bike and, when I stripped the engine some 20,000 miles later, the bush conversion was still fine. Steve knew his stuff.”
By then, Jon was totally hooked on classics – and BSA twins in particular. He café-racered his A10 and rode in that guise for a few years, bought one of the (then new) Mistral Engineering electronic magneto conversions through Steve – for whom he was working by then – before taking the faithful old BSA off the road in the early 1990s and stripping it down. But, by then, Jon’s life had taken something of a turn.
“I’d been working for Steve alongside Gary Hearl [now another of SRM’S directors],” Jon explains. “Steve’s original SRM workshop was compulsorily purchased as part of the redevelopment of Cardiff Docks, and Steve opted to go back to being a one-man band, so Gary and I decided to take the plunge and bought SRM from him in 1992. That’s when we moved up to Aberystwyth. While we were building up the business, the old A10 stayed in bits – but by 2000, I thought it was time to get it sorted out.”
Since buying the bike back in 1980, Jon’s knowledge of A10s had come on in leaps and bounds. When he bought it, Jon’s bike had an iron-head Golden Flash engine, but in the meantime he’d bought a Super Rocket engine from the States and decided to upgrade – as well as rebuild – his first big bike using the best combination of parts he could find. That included the Super Rocket engine and, naturally, a lot of components from the company he co-owns with Gary Hearl and Geoff Dewhurst.
“Basically, I’ve built the engine to Rocket Gold Star specification,” Jon reveals. “Most of the SRM parts I’ve fitted are the prototypes for our production items. The old A10 has certainly served us well as a test-bed for new products over the years. Although I didn’t realise it at the time, when I bought the bike back in 1980 it had parts from just about every year of A10 production. It had a circa 1955 frame and rear subframe, fuel and oil tanks and a toolbox from around 1959-60 and a 1956-57 Ariel front hub. It’s definitely far from an original bike.”
It might not be original, but there can’t be many bettersorted A10s anywhere. The engine has been completely rebuilt – and by someone who knows BSA twins better than most. It has the SRM needle-roller main bearing conversion, Cnc-machined billet conrods, a Spitfire 357 cam, an SRM high-delivery oil pump, and a Rocket Gold Star head with bigger valves and lead-free compatible seats. “I’ve gone with 8.5:1 pistons, though,” says Jon. “If you go any higher, you get problems with pinking and have to retard the ignition so much it’s not worth it. As it is, I’ve had the bike on our dyno and it makes 42bhp.
“I still have the Minstrel Engineering magneto conversion, but the bike has one of our SRM mag conversions on it now. I’ve converted the electrics to 12-volt and fitted a modern electronic regulator, as well as one of our belt-drive kits for the dynamo. I’ve stuck with an original six-volt dynamo – it’s the regulator that controls the voltage anyway. The six-volt unit doesn’t start to charge until the engine is turning over at around 1500rpm – a 12-volt dynamo will charge from about 1000rpm – but that isn’t a problem in use. The dynamo is rated at 60W, though, so I am limited on total power consumption. I use a 35/35W halogen headlight bulb, and using an LED rear light is a good idea.”
Like the engine itself, the primary drive and gearbox have been uprated, too. “Years ago, NEB designed an alloy clutch and belt primary drive for racing Gold Stars,” John explains. “We adapted one to fit an A10 and it worked pretty well. It was a bit jerky, because it had no cush-drive on the front pulley, so we modified a stock A10 cush-drive to fit inside the NEB front pulley. We produced a batch of new hex-nuts to attach the front pulley to the end of the crank, so you can torque up the nut to the correct 65lb ft. You can’t really do that using a C-spanner on the standard nut.”
When he rebuilt the bike in 2000, Jon fitted an RRT2 gearbox, but admits it wasn’t the best idea. “I put up with it for about a year,” he smiles. “It wasn’t ideal for the Welsh mountains. There’s a really steep stretch of road out towards Tregaron called the Devil’s Staircase. It’s not just steep, it has really tight bends, too. I ran out of steam in first gear on the A10 going up there one time and almost fell off trying to turn the bike round to roll it back down the hill. When Nova Racing Transmissions brought out their fivespeed gearbox for the A10, I bought one of those and fitted it. It’s transformed the bike. It somehow feels more lively.”
Jon’s also ditched the standard Amal carburettors in favour of a pair of 30mm Mikunis. “I fitted them to try them out,” he says. “We worked with Allens Performance [the UK Mikuni distributor] to develop kits for A65s, Triumph T140s and T120s, as well as the A10. Mikunis work so well, but you do need to get them set up just right – we used our rolling road and four-gas analyser to do it.”
It’s not just the engine and transmission that have been upgraded – the rolling chassis isn’t pure A10, either. “The forks are from a 1966 A65,” Jon reveals. “They’re the double-damped type, much better than the originals. I’ve got Ikon shocks fitted, but I’ve had some custom dual-rate springs made to fit inside the covers, which we fabricated in-house. The covers wouldn’t fit over the Ikon springs.
‘MOST OF THE SRM PARTS I’VE FITTED ARE PROTOTYPES FOR OUR PRODUCTION ITEMS’