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Norton girder fork damper question.

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Norton girder fork damper question.

Posted by nicholas_reeves at March 11. 2017

Could someone please explain how the fork damper works and what does it do.Thanks.

Re: Norton girder fork damper question.

Posted by iain_brown at March 11. 2017

Hi Nicholas,

there is a friction disc in each side, when the nut is tightened these get squeezed and there is more friction.

With zero damping (friction) the front end would be like a pogo stick bouncing along.

The problem with friction damping is that the coefficient of friction is typically higher a low movement speeds, so too tight and small bumps are harsh, but big bumps can still have you bouncing along.

The other trick is too much grease on that spindle and the discs can get coated in grease, not very helpful for the friction.

 

cheers

iain

Re: Norton girder fork damper question.

Posted by George Phillips at March 11. 2017
Interesting point, Iain. I would have thought that the coefficient of friction was the coefficient of friction and not related to the relative velocity of the mating surfaces? Maybe the "hardness" at low speed is more to do with the force needed to overcome the inertia of the initial resistance. Once the surfaces are moving the CoF will be same. Anyway, all very academic. How does one over come this problem?

Re: Norton girder fork damper question.

Posted by ian_cordes at March 11. 2017
Previously George Phillips wrote:
How does one over come this problem?
Invent hydraulically damped telescopic forks, George...!

Re: Norton girder fork damper question.

Posted by robert_tuck at March 11. 2017

Previously ian_cordes wrote:

Previously George Phillips wrote:
How does one over come this problem?

Invent hydraulically damped telescopic forks, George...!

Fit a hydraulic damper inside the spring box ,like some rudge's have.

Re: Norton girder fork damper question.

Posted by ian_cordes at March 11. 2017

A far more sensible answer than mine, Robert!

Ian

Re: Norton girder fork damper question.

Posted by robert_tuck at March 11. 2017

I have to confirm that finding the right setting is not easy as it does vary with the speed and that yes overgreasing the forks is a no no as it results in the friction disc's being totally inefective untill they jam solid. A concealed hydraulic damper is on my list.

Re: Norton girder fork damper question.

Posted by nicholas_reeves at March 11. 2017

Thank you all for your input.Could someone tell me a rough Base setting ie how many turns out from fully tightened to get a half decent compromise. Many thanks again.

Re: Norton girder fork damper question.

Posted by robert_tuck at March 12. 2017

On the Rudge the suspension only seems to "work" at speed  ,say over 60 mph ( it is after all a near copy of a Grand Prix machine) , the damper is only lightly applied otherwise on a bumpy road you are well and truly banged about. Less racy bikes may have better low speed action.  Tire pressures are lower than modern bikes .

Re: Norton girder fork damper question.

Posted by richard_payne at March 12. 2017

1930s Norton forks with the rebound springs fitted are really rather good and don't need a lot of side-damping.

On the WD bikes for some reason they deleted the hand wheel and any adjustment has to be done with a hexagon nut which doesn't make it so easy when on the move (perhaps this was the intention ?)

I find that with a gloved hand on the hex, I can slightly over-tighten it and then need to back off just a fraction.

It should really just be providing some resistance to counteract the tendency to pogoing oscillation that can occur over a sequence of irregularities or if you become airborne and land nose first.

I don't like much steering damper either for normal riding. Just a tiny bit of drag.

Re: Norton girder fork damper question.

Posted by nicholas_reeves at March 12. 2017

Thanks for your reply Richard.I tried to turn the wheel adjuster today but it won't move.I even tried undoing the bolt that goes through it and the nut the other end.Any idea why it won't move or am I doing something wrong. Thanks.

Re: Norton girder fork damper question.

Posted by richard_payne at March 13. 2017

The spindle is (the hexagon head of which you're seeing) has a shoulder and is threaded into the left hand link. It should not therefore turn and the nut on the left hand end is purely a locknut.

The hand adjuster should be able to turn freely until it is fully in or out. There is a star shaped spring behind it with a detent in the side plate.

If it won't move,  the problem will most likely be corrosion. Without knowing the condition of the bike, it's difficult to advise but I would certainly think that the forks need a through inspection as if they are not correctly assembled and lubricated, they may not be safe.

You could try trickling some penetrating oil around the spindle head in the hope that it will work down the threaded section.

Re: Norton girder fork damper question.

Posted by David Cooper at March 13. 2017
Nicholas Maybe the following link to 'Webb Fork Adjustment' will assist. http://velobanjogent.blogspot.co.uk/2011/06/webb-girder-forks-general-look-at-some.html As Richard says - one end of each spindle has a plain spigot through the link. If the locknut is loosened, turning the spindle just rotates it in the link. But the other end is threaded into the link. If the spindle is turned clockwise, it screws itself into the link and thus pulls the ling outwards, slackening the clearances (which is sort of counter-intuitive to begin with). Original grease nipples (now unobtainable) have plain ends. Modern ones have a button to take a clip-on high pressure grease gun. If you cannot get grease into the plain type, you can replace them one at a time with a modern one and use that until the grease gets in. Then either replace the old one or post it to me! Two of mine have lost the little non-return ball and I like the look of the old ones. The old ones seal quite well with a push-on grease gun if you put a small scrap of clean fabric on first and pump through that. It helps sealing. Annoyingly I find I need amore than one size of grease gun to get in everywhere.
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