Why a [360°] parallel twin?

Matt Spencer · Sep 13, 2022

Wondrering if the Nortons dragging the Pegs on your mountain road . & or is a Mk III . of a comparable weight . FIVE HUNDRED AND FOUTEEN POUNDS .

Bonnevilles not weighing 400 .

https://magazine.cycleworld.com/image/spread/19730102/32/0

ANYWAY , the SPEED TWIN was the ' Twin Single ', and a huge leap forward , pre war .

looks just like the yanmaha .

Perhaps theyre not fast enough ? . Abarft Me eartys .

Alan L · Sep 14, 2022

acotrel said:
When I was a kid Triumph 650s were common and Norton Twins were rare. My mate had a Manxman and it was excellent, but most Norton Twins were 500s with single carb. They handled very well but were a bit slow. In those days, a lot of us obsessed about road racing. If you bought a Manx, you were almost immediately promoted into A grade. I always believe in Norton, because of their racing record. The cylinder head on the Commando, makes much more sense than a Triumph Bonneville head. When the Commando was designed, it needed to compete with the CB750 Honda for commuter sales. Most people did not need a fire-breathing sports bike.
If I had designed the Commando, Norton would have gone broke even sooner. The hole in the bob-weight and the isolastics are naff. If it vibrates, raise the balance factor and ride it faster. Japanese bikes are for tootling around town, and screaming away from traffic lights - not riding at moderately high speeds on long winding roads.
The only modern bike I have ridden was a VTR400 Honda, It was speed limited to 180 KPH - what is the point of that ? At 180 KPH, you still lose your licence and cop a big fine, so you might as well go fasrter.

Hi Acotrel,
what makes the Norton cylinder head a better design than the Triumph’s?
regards
Alan

baz · Sep 14, 2022

Alan L said:
Hi Acotrel,
what makes the Norton cylinder head a better design than the Triumph’s?
regards
Alan

Basically it's a lot shallower ,far better combustion
You don't get the pinking you get with a triumph head
So you don't need extremely high crown pistons to get high compression
The valves in a triumph head are at more of an extreme angle that means the rocker gear pushes the valve sideways promoting valve guide wear

concours · Sep 14, 2022

Matt Spencer said:
GEARING .

POWER.

cash · Sep 14, 2022

olympus said:
Hi guys, with all the inherent issues with a parallel twin engine design over a 180 degree twin, why did Norton & indeed the majority of the British motorcycle industry go down the parallel twin road??
I cant believe the technology & tooling wasn't available at the time so was it down to cost or just dog headed management?

I'm pretty sure it was down to the cost of a parallel twin magneto against a V twin magneto.

Alan L · Sep 14, 2022

Well,
Isn't the history of all human endeavour a strange thing.
One could say the entire future of British bikes hinged on a decision to save a few bucks by not needing a V twin magneto (and extra carby). From that moment forth, through a cascading string of events, pommie bikes were destined to become effectively extinct by the mid seventies.
I suspect it really tells us a lot about how broke the Brits were after the war, how little money the working class man had to spend on discretionary items like fast bikes and how tight the profit margins were in the motorcycle industry.
Some may also say it all tells us of the parsimony of management, their myopic short term thinking and their desire to return profits to shareholders over the long term security of the industry. I of course would never say such a thing.
regards
Alan

EstuaryBoy · Sep 14, 2022

Post war people wanted their own transport, not toys, purchase price (and availability!) would have been greater factors than top speed for most.
Not sure when rationing stopped here but it wasn't on VE Day :-(

(Just googled: 'when the Queen came to the throne in 1952, sugar, butter, cheese, margarine, cooking fat, bacon, meat and tea were all still rationed. Rationing did not actually finish until 1954, with sugar rationing ending in 1953 and meat rationing in 1954.')

No mention of motorbikes, though

baz · Sep 14, 2022

EstuaryBoy said:
Post war people wanted their own transport, not toys, purchase price (and availability!) would have been greater factors than top speed for most.
Not sure when rationing stopped here but it wasn't on VE Day :-(

(Just googled: 'when the Queen came to the throne in 1952, sugar, butter, cheese, margarine, cooking fat, bacon, meat and tea were all still rationed. Rationing did not actually finish until 1954, with sugar rationing ending in 1953 and meat rationing in 1954.')

No mention of motorbikes, though

Hence the abundance of bicycles with clip on motors so people could get about
A certain Mr Soichiro made one too I believe

Why a [360°] parallel twin?

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