Motorcycle General Discussion

[peak4Participant @peak4]

I do like the look of those, but have too many bikes already.
I still need to re-assemble the Ducati at the moment.

Bill

 

[John MCParticipant @johnmc39344]

Interesting bike, would like to try one.  Getting back to the bent spokes.  Google found me a number of images that showed bent and straight spokes, 2 and 3 cross spoke patterns.

These bikes were popular sidecar tugs.  These put far greater loads on the wheels than a solo so why would they use bent spokes?   How can the spokes be tensioned properly with a bend in them?  Was this what the manufacturer specified?  I would need some evidence of that and of the perceived advantages.  Why only the front wheel? Was it just a sales gimmick?

Getting back to this particular bike, unless the photo is playing tricks, it’s got the wrong rim, the nipples are not sitting properly in the dimples.  I would also fit straight spokes unless evidence supporting bent spokes comes to light.

This brings to mind misinformation about spoked wheels in the world of moto-cross some years ago.   One should bind spokes, where they cross, with wire.  The reason being that when a spoke is at the “bottom” (6 o’clock), it will be in compression, wiring them together will help the spokes support the weight……..

 

[Ian ParkinParticipant @ianparkin39383]

This is a screen grab from the English translation of the nimbus maintenance manual

[Michael GilliganParticipant @michaelgilligan61133]

Clearly a post-facto document, produced for the benefit of modern owners.

It describes the situation well, but doesn’t explain the why.

MichaelG.

[WearyParticipant @weary]

The document above posted by Ian Parkin references the ‘bent spokes’ being fitted from Frame No.8501, which would have been produced during 1949.   So, seemingly, only the last 11 years’ production would have ‘bent spokes’, the first 14 tears’ production, the majority of the production, would have had ‘straight spokes’?

Perhaps the spoke-change is associated in some way with the ‘high fork’ introduced in 1948?

Ah!  Found this on the Nimbus facebook group in response to an enquiry:

‘The plan was to reduce the radial pull on the brake drum, thereby reducing the amount of drum distortion. F&N were full of good and sensible ideas; this was not one of them.‘

(F&N = Fisker and Nielsen)

Note: facebook group seems to be ‘public’ so no need to be a facebook member, simply click the ‘cancelling x’ on the first ‘pop-up’ and you are in.

Phil

[Ian ParkinParticipant @ianparkin39383]

Whilst mine is a 1946 model it has been fitted with the high forks as weary mentions

also its had a newer engine fitted at some stage after 1956

can anyone translate danish…this document came with it..looks like a mot type test cert

[CirclipParticipant @circlip]

As an inline four, do your legs get ‘warm’ and how is cooling affected? Ariels Square four was a nightmare.

Regards  Ian.

[Ian ParkinParticipant @ianparkin39383]

Circlip

I have only had it a month or so so riding it at the moment its been cooler weather

this is a sport model (22 hp) so higher compression …the carb is tiny throat perhaps 20mm

i’ve not noticed the block getting too warm yet

[Ian ParkinParticipant @ianparkin39383]

The electrical system is quite good for the period

the crank has a bevel gear on the front end which drives the dynamo/generator which you can see at the front of the engine at the top of the generator there’s another bevel which drives the cam shaft

the ignition is all built into the distributor cap coils points etc

the light switch is nowhere to be seen….its on the left hand twist grip. …off ,side lights,dip head and main beam 4 positions in total

the ignition switch is built into this complicated switch which is on the dashboard along with charging light

 

[Ian ParkinParticipant @ianparkin39383]

I have ordered a few parts from the nimbus shop in Denmark at i thought very reasonable prices and they came in 8 days..

it seems that everything you could need is available new and larger items used

[John MCParticipant @johnmc39344]

‘The plan was to reduce the radial pull on the brake drum, thereby reducing the amount of drum distortion. F&N were full of good and sensible ideas; this was not one of them.‘

That answers the bent spoke question.   I think it compromises the “strength” of the front wheel.   If the spokes are tensioned properly the brake drum can and most likely will be pulled out of round.  A good wheel builder will be able to minimise this but better still, machine the braking surface after building the wheel. (And machine the linings to fit the drum).

Going slightly off this topic.   As far as I know, Velocette was the only British factory to machine the braking surface after the wheel was built.  Triumph and BSA didn’t, their wheel builders took care to try and maintain roundness of the drum.  Norton were notorious for out of round drums after wheel building.

 

 

 

 

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