Good question(s).........as to the "How", if we take a look at the right side of the machine we can see that the innovative builder has aligned the BSA A10 crankshaft with the input shaft of the Sunbeam gearbox, which then of course drives the rear driveshaft to the driving wheel.
As to "Why?"...............I guess just because he wanted to prove it could be done! LOL!
The "goldfish" is an Ariel (Golden) Arrow, a 250cc two-stroke twin. They may look a little strange today, but believe it or not they were innovative at the time and extremely well received, they were even voted motorcycle of the year three years in a row along with their Ariel Leader brother, which had enclosed weather paneling.
We have to remember this was 1959 and the Japanese hadn't arrived on the market with their Honda CB77s, or Yamaha YDS3s or Suzuki T10s yet, and the Ariel Arrow sold in great numbers to an eager British youth who were restricted to 250cc machine until they had passed their full driving test.
The Ariel Arrow looked sporty for the era, was extremely reliable and easy to work on and was as fast as any other similar machine. And there was little other choices at the time, a 250cc BSA C15, a 250cc Royal Enfield Crusader, or a 200cc Triumph Tiger Cub, all single cylinder machines.
My first motorcycle was just such an Ariel Arrow, a 1962 model, for which I payed £85.00......all the money I had in the world!!!
I believe this is the only Rocket 3 I’ve seen with a BSA tank. Usually a Triumph badge. Allred, can you please fill me in?
Ah, you are getting confused. ALL Rocket 3s have a BSA badge. The Triumph Trident has a Triumph badge.
Both machines were developed together based on the 500cc Triumph 5TA engine, but do differ in several ways. The BSA has inclined engine cylinder bores, whereas the Triumph's are vertical. And the BSA has a duel downtube cradle frame, whereas the Triumph has a single downtube frame.
The American market hated the initial "Bread-Box" gas tanks, and the "Ray-Gun" mufflers, so both machines reverted to the old-style gas tanks in later production models. Initially they were all 4 speed gearboxes, but later models had 5 speeds. Later models also had electric starts and disc brakes.
I believe that the very last models (1975) adopted the slanted cylinder engine in both the BSA and Triumph versions, they said it produced a better weight balance, but maybe they just had more BSA engines left over than Triumph ones?