Could one of you knowledgeable gentlemen please explain the advantage of the small springs fitted to the sides of some girder forks, for example Nortons and if they were useful why didn't all manufactors fit them. Thanks.

Hi Ian...the springs you refer to are 'check springs' and are under tension when the forks are assembled. The main spring provides resistance to upwards movement of the wheel, these springs control the downward movement and 'damp' the rebound force exerted by the main spring.
BSA forks, for example, rely entirely on the 'not very good' friction damper on the side of the forks to perform the same function.
A number of makers employed check springs and I would say they provide a more reliable method of doing the job as friction dampers rapidly wear causing their performance to reduce substantially. Also, in the brief period after fitting when a friction damper is working efficiently it exerts resistance to movement in both directions, when really only resistance to downwards movement is needed.
I have thought of fitting these springs to my M20...although not a standard fitment originally on any BSA fork.
Each manufacturer made their decision about whether they were necessary, much as today modern telescopics have varying degrees of 'adjustment'...Ian

email (option): julie@wright52.plus.com

The other problem with the friction dampers on the forks, on my Norton at least, is that the grease from the spindles finds its way onto the friction disks with obvious loss of friction damping.
I wonder whether the check springs truly damp the response (which requires some sort of energy loss) or are more aimed at fine tuning the varying spring rate. The barrel shape on the main spring gives a variable rate (progressive) spring, the more it is compressed the stiffer it gets, and the check spring movement differs from the main spring due to the leverage of the links.
Interestingly (to me at least) the check srpings on the race Nortons were cylindrical shaped (ie not progressive) whereas those on the road bikes were barrel shaped (progressive).
Cost would be a good reason not to include them, Norton's were never a cheap bike.

Check springs on my WNG are giving me a headache trying to fit this morning, I have come in to make a cup of tea while I have a think about it , shame to damage the fresh paint,Is there an easy way? off to pick up my RE CO from peter skelton at lunch time now he has fixed the tin and paintwork,after the bloke ran into me back in the summer while I was waiting at a level crossing,HE WAS ON THE BLOODY PHONE, Will drain petrol and have in my entrance hall for a while,By the way this CO has a good ride with the check springs,but have a CO frame without them, friction damper instead, due to build this into a CO for my daughter sara will post a pic of the RE CO in the house! andrew.h.

email (option): warbikes@gmail.com

Thanks for the replies, I was thinking about making some links and fitting some to the girders on my M33.Re fitting the springs to the Ariel could you not tap some washers in between the coils, this will lengthen the spring allowing it to fit then when you push down on the bike the springs will stretch causing the washers to full out, this is how I fit stand springs.

Hi Ian..Surely if the check springs are put under increased tension on the rebound they are then 'storing' energy?...So there would be an energy loss (or transfer) from the main to the side springs...Ian

email (option): julie@wright52.plus.com

I can now understand the principle of fitting check springs, because as you say the energy stored in a spring as in the central of the girders,when the spring is compressed the energy released causes the forks to pogo up and down until the energy is gone, but the check springs working in the opposite direction would help to damp down the main springs ability to do this along with the friction dampers.
I think I will still have a go at making some links up and fitting some check springs to the M33 just to see if there is an improvement.

Hi Ian..I am sure there will be an improvement. As I said I may well carry out the same job myself when I rebuild my M20. I'd be interested to know the results of your mod....Ian

email (option): julie@wright52.plus.com

Whether a spring is in tension or compression its effect will be the same, to alternately store and release energy. In the absence of any friction or other damping it will bounce forever, alternating between tension and compression - obviously not possible in the real world as there is always friction.
Having thought about it further what may have been an aim is that a spring system will have a resonant frequency - on a motorcycle front end this will be when it will most want to pogo, for instance if you hit a series of bumps in sympathy with this frequency.
Having two sets of springs tuned at different non sympathetic frequencies might minimise this effect, so in effect be a type of damping, reducing the demands on the friction dampers by minimising any tendency to pogo??

As I understand it the reason that there tends to be two valve springs on a valve is to damp down the resonates in the larger spring.

There's too many Ians on this thread...I'm getting confused...other than that I tend to agree with the conclusions so far...Ian

email (option): julie@wright52.plus.com

The fork set-up on my 16H is in unworn condition and the action is very controlled. It's probably an exageration to say that it feels damped but it doesn't get into the sort of bouncing, clashing frenzies that some girder set-ups seem capable of.

So that will be M20 forks then...on that point I will happily concede the superiority of the Norton design..Ian

email (option): julie@wright52.plus.com

'tis the season of goodwill, Ian. No names, no pack-drill !

...I was actually thinking of some of the continental lightweights that I've ridden alongside in a state of shock and awe !

Hi Ians and all,
Here is my solution to fitting outrigger springs cheaply and without too much modification. I just stretched a couple of long bungees round the fork blades and lower yoke. This really improved the damping and handling on the G3, and can easily be removed for "originality"
Cheers, Mick.

email (option): mick@motorbikemike.org.uk

I notice the threaded ring holding your speedo cable on is adrift Mick!! My Matchy girders work perfectly with the damper done up a tad. No grease on mine! But as Ian mentions, it damps the compression as well causing a little jarring on potholes!

Hi Douglas, The damping on compression was the main thing I wanted to eliminate as the "roads" I use to get to work are little more than cart tracks, and getting worse. Plus I'm a fat git and the spring needs all the help it can get!
Yes the speedo cable does that. Cheers, Mick.

email (option): mick@motorbikemike.org.uk

Mick is just keeping the speedo cable undone on the G3, so it isnt showing too many miles on the clock when he comes to sell it, Nothing sells better than a low milage model, Isnt it called CLOCKING!!! andrew.h.

email (option): warbikes@gmail.com

Clocking? WTF are you on about? The thread on the speedo is a bit dodgy and the nut unscrews itself. I bought this bike in 1986 from a chap who bought it from Dawsons Motors in 1954. There is no way its for sale while I'm able to ride it.

email (option): mick@motorbikemike.org.uk

Mick only kidding,hope no offence taken, Happy new year A.h.

email (option): warbikes@gmail.com

It's too late now Andy! Mick has gone into a big sulk. There will now be a huge delay for any parts you order for that WING Ron

email (option): ronpier@talk21.com

O dear Ron , still need an oil pipe that was out of stock when last ordered, Now wheres that bit of old plastic I took off the bike. Happy new year to you , thanks for the help with the resto on the WNG, andrew h

email (option): warbikes@gmail.com

Hi guys, sulk? me? I think not. Just come round from the new year lemonade drinking. Now even fatter, will need more bungee spring helpers!
Happy new year everyone, ride safe, hope to see you all in Normandie.
Cheers, Mick.

email (option): mick@motorbikemike.org.uk

Well done Mick. See you in June. Ron

email (option): ronpier@talk21.com