From our Old Bike Archives – Issue 71 – first published in 2018.
Story and photos: Jim Scaysbrook
BSA 650 twins came in such a varied array of models that there is today, fifty four years after the final pre-unit models emerged from Small Heath, confusion as to which model was which. And for a company as conservative as BSA, the title Road Rocket must have caused the Board much deep consideration, yet it was to prove to be the ultimate example of their pre-unit parallel twin.
The lineage began with the A7 of 1946, but had its roots pre-war in the prototype 500cc overhead camshaft vertical twin of 1938/39, which for obvious reasons failed to progress for the next seven years. When it did, the engine followed the Triumph example, being a pushrod design that has been variously attributed to Val Page, Bert Hopwood, Herbert Perkins and David Munro. Whoever really did most of the legwork is immaterial these days, but he or they did a fine job, because the basic layout penned in the late thirties stayed in production for 17 years. Even when the pre-unit design gave way to the new unit construction A65 in 1963, the basic engine specification remained: a 360 degree twin with a single camshaft located at the rear of the crankcase operating the pushrods. The patented camshaft layout distinguished the BSA design from its rivals, with Triumph, AJS/Matchless, Royal Enfield and Ariel all opting for twin camshafts, placed in front of and behind the cylinders. Norton was the sole exception, but their single camshaft sat at the front of the engine.
The 62mm x 82mm 495cc A7 also differed from most in having the four-speed gearbox bolted to the crankcase, rather than housed in engine plates with means of adjustment for the primary chain. Three years of healthy A7 production passed before the inevitable capacity increase occurred in 1949, but although the 70mm x 84mm 646cc A10 looked very similar to the A7, it was actually a completely new design. On the 650, the engine and gearbox were separated, as on most of the opposition. Finished in a fetching polychromatic beige and christened the Golden Flash, the A7’s big brother proved popular from the outset, although the US market was clamouring for a sports version. This appeared in 1953 as the Super Flash, and the following year the home market got their own sporty twin, the A10RR Road Rocket, which also featured the new swinging arm frame in place of the plunger chassis. Also new was a light alloy cylinder head, replacing the old iron item, but this retained the siamesed inlet port that would take only a single carburettor – a feature that remained until the end.
Despite its evocative title, BSA intended the Road Rocket to be a sports/tourer rather than an out-and-out performance machine, but few customers saw it this way. The optional tachometer and TT carburettor addressed the need for speed somewhat until in 1957 the Road Rocket was quietly phased out and replaced by what was initially called the Super Road Rocket, which was quickly abbreviated to Super Rocket. With improved cylinder head porting and a higher compression ratio to make use of the slowly improving fuel quality, the A10SR also gained a stiffened crankshaft. Gone too were the Ariel hubs used on the A10RR, replaced with a new full width BSA design front and rear. These were cast iron rather than alloy with straight-pull spokes – 8 inch on the front and seven on the rear, with both brakes cable operated. New less restrictive and rather noisy silencers assisted in the quest for power.
The new Super Rocket was to have been released at the annual Earls Court Show in November 1957, but when the show was cancelled it was left to BSA – and most other manufacturers – to stage its own model releases. The A10SR poked out 43 bhp, despite a 1 3/16” Amal Monobloc carburettor being used instead of the Road Rocket’s Amal TT9, which was available as an option.
Specifications varied between the UK and US models, notably with regards to performance. For the 1959 model year, the US Super Rocket was available in a Sapphire Blue colour scheme, with bigger valves in the cylinder head, a slightly larger carburettor with inlet port enlarged to match. Inlet valve size increased from 1.455” to 1 ½” and these engines were externally identified by a modified tank transfer with ‘Big Valve’ splashed across the symbolised rocket leaving planet Earth. The ‘Big Valve’ engine became the standard fitment from 1960.
Detail changes were made to the Super Rocket over the next four years, and in 1962 the final incarnation – the now highly revered Rocket Gold Star, appeared. The RGS was the result of combining the tuned 650 engine with a Gold Star type frame (without the kink in the lower frame tube to clear the single’s oil pump) and front forks, with a Siamesed exhaust system and a single silencer. Compression was raised to 9.0:1 and power was up to 46 bhp. It was catalogued with an extensive list of options and as an obvious tilt to the Gold Star, the fuel tank was sliver with red lines surrounding chrome side panels. As it neared the end of its life, the Super Rocket also gained the 9.0:1 pistons and the camshaft from the US-spec Spitfire, and the RGS Siamesed exhaust system was also available as an option, but in August 1963, the old twins were no more, replaced by the new unit construction A50 and A65.
A Daley ride
Our featured BSA Super Rocket is owned by former Australian Motocross and Dirt Track Champion Matt Daley from Brisbane, who found the bike in Melbourne in 2015 with the help of his mate Barry Taylor. “It had basically been built up around an engine that (BSA guru) Mike Reilly brought in from USA,” says Matt. “The owner sourced all the other parts and a lot of this – the frame, wheels and so on – came from Mike Reilly as well. Unfortunately I would have to say that the owner’s mechanical skills were not all that great. I haven’t touched the engine but virtually everything else I had to strip and rebuild. I owned a Golden Flash in my younger days and I always really wanted another BSA twin, and I guess the Super Rocket is as good as you can get in the pre-unit construction models. This one had some worthwhile modifications, such as the 12 volt electrics to replace the 6 volt system. It had a new carb on it but from what I understand these Amal carbs can come from China, India or Britain, and this one just did not work, I could never get it to idle. So I bought a new Monobloc from Burlen Fuel Supplies in England and it is absolutely spot-on. The ignition is fine too – I don’t exactly know who made the unit but the bike starts first kick, but I am planning to fit a BTH Electronic unit at some stage.
Fortunately Matt is an experienced engineer, but it took him two years to get the BSA to his satisfaction. The brakes had been relined with too much shoe clearance and Matt had this rectified by Rod Cook in Brisbane. The brakes Matt now describes as ‘adequate’. Far from being a static exhibit or a show pony, this Rocket is ridden regularly, and fairly briskly. “I reckon you could ride this (from Brisbane) to Cairns no worries,” he says. “It’s such a buzz to ride and it has the later type fibreglass-lined straight through mufflers so it had a wonderful exhaust note. I fitted new Avon tyres which look right and work really well, but it shows up the limits of the handling because there’s not enough ground clearance and the side stand grounds easily. I think it actually handles really well and the suspension is pretty good, but you notice the weight, it’s a heavy bike and even still has the lugs on the frame to fit a sidecar. I have a new BMW R1200GS which is a great bike, but I enjoy the BSA so much, I wish I could ride it more. I feel sorry for the younger generation who are missing out on riding something like this.”
Editor’s note: Sadly, Matt Daley passed away in November 2021.
Specifications: 1962 BSA Super Rocket
Engine: Parallel twin OHV.
Bore x stroke: 70mm x 84mm
Capacity: 646cc
Compression ratio: 8.3:1
Carb: Amal Monoblock 1 3/16”
Ignition: Lucas magneto
Power: 43hp at 6,250 rpm
Weight (dry): 418 lb (190 kg)
Wheels/tyres: Front: 3.25 x 19, Rear: 3.50 x 19
Brakes: Front: 8” single leading shoe. Rear: 7” single leading shoe.
Wheelbase: 1422mm
Seat height: 762mm
Ground clearance: 152mm
Fuel capacity: 4 gallons/18.2 litres
Top speed: 108 mph
