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FF: Forks Modified Steering Stem

timetraveller

Well Known and Active Website User
VOC Member
Gentlemen, assuming that we survive the present problems then the question is 'are there any people who might want to order the modified steering kit'? The reason for the question is that I have three left which Greg Brtillus requires and after that I will have run out of them. I now have two people who have expressed an interest in ordering in the next few months. I have to get them made in a batch of ten in order to keep the price down (CNC set up costs). I do not mind having a few left on the shelf but as it costs nearly £3,000 to get a batch of ten made then I do not want £2k+ sitting on the shelf for years. So, without making a definite commitment, if you are potentially interested would you please let me know. You can either PM me or email me on enw07@btinternet.com Thank you in advance :)
 

MarBl

New Website User
VOC Member
Hi,
I am new in the Vincent world, having recently acquired a Rapide, which is non matching numbers and meant to be used regularily.
I already studied several threads including this one about the uniqueness of the Gridraulics and I'm definitely in for the next batch of the modified steering stems.

But after inspecting the specific setup of my forks, another question about the interaction between damper and fork arose.
I found an armstrong damper installed with short eyebolts. Now usually its said, the armstrongs should be installed with long eyebolts. However as far as I understand it, the armstrongs have a reduced travel. I measured 2,4". But using long eyebolts doesnt bring back travel, it only moves the available 2,4" to the lower travel path of the forks, where the main problem seems to be located, the "backward rolling front wheel" necessity causing the brake/fork lock.
So given the damper-caused limited travel, wouldnt it be better to use the upper part of the fork travel and therefore keep the short eyebolts? Additionally I would remove both inner springs to get the forks full action in the 2,4" range of the upper part of its travel. It seems less of a problem if it bottoms out occasionally rather then top out, if I understand it correctly. Also the bike is meant to be ridden solo 99% of the time with my 75kg.
So I am considering such a setup as a first crude treatment before a modified stem is available and I would be very interested in comments and further advice.
Thanks in advance
Cheers
Martin
 

Albervin

Well Known and Active Website User
VOC Member
Martin, welcome to the world of Vincents. For every question there will be multiple answers and at least five of them will be correct even though they are different. Regarding front suspension. The girdraulics do NOT work the same as telescopics so get that out of your head now. The relationship with Armstrong shock absorbers and long eye bolts is that under heavy braking the forks can cause the front mud guard to impact on the magneto cowl IF short eye bolts are used. If I can make a suggestion. Fit short eye bolts and an IKON front damper. With the Aussie dollar so low this is a good economic idea. E-mail Geoff at IKON and ask for a FRONT damper for a Series C Vincent. THEN, buy two Series D front springs and fit them. That should give you a very good starting point at what a Vincent should do. There are many other ways of adjusting/modifying the front suspension. These include an hydraulic steering damper. A Kawasaki item is often used and the bracket set-up is well documented in the archives. The standard steering damper should be a twin disc set-up and always "nipped" but not tight. Tyres and tyre pressures play an important part too. This can be complex and best left to later BUT always maintain at least 26 psi in the from wheel. Another important aspect is the greasing and adjustment of the forks. It is important that the bushes are well lubricated and the spindles are not too tight or too loose. Those chrome dust caps should just be able to be rotated without force; they should not be able to be moved from side to side at all! There will be someone who lives not too far from you who can assist.
 

timetraveller

Well Known and Active Website User
VOC Member
The way that I imagine this is to consider the Armstrong damper as just a short damper when compared with the original Vincent one. If you accept that and the fact that the upper eye is still going to have to fit into the same place at the top then the only way to make the geometry the same as original is to bring up the lower mounting by using extended eyebolts. If you just remove the inner springs then it is true that the front end will sink down but you will almost certainly find that the front end will bottom out frequently. David Dunfey came up with a solution several years ago and that was to use shorter stiffer springs at the front. This gave different pre-load and a shorter stiffer movement. His original suggestion of 75 lbs/inch springs at the front proved too soft for all but the lightest of stripped down racing bikes and he had to design three different spring strengths. I had several sets of these made for people until I met John Emmanuel and understood what he had done. This is a much more sophisticated method that alters the geometry and thus the path of the front wheel movement. I had several copies of John's system made and then realised that it was also possible to alter the comfort and front wheel control by modifying both the front springs and the damper.. It took some more time before I also realised that one has to think about the front suspension in a slightly different way. It does not matter whether it is a single or a twin, the un-sprung weight at the front is the same; forks, wheel, spring boxes, mudguard and stays, headlight etc. It also became clear that weight at the rear, passenger, pannier boxes etc also seems to make very little difference to what is required with the front suspension. It is the weight of the rider, fuel tank, UFM and the engine/gearbox unit which are being controlled and it is a combination of springs and front damper which do this. What really made me understand this is when the 20 stone/127kg test rider changed from Oilite to needle roller bearing at the front and we had to go to a stiffer damper and stiffer springs with less pre-load. The more people who give feedback on their use of the new front end the better I will be able to judge what the best combination of springs and damper will be. For example, over the last couple of days I have been in correspondence with one of our German friends who weighs 17 stones/108 kg and has a Comet. That weight combination suggests either 36lbs/inch springs and a normal AVO damper on its stiffest setting or 45 lbs/inch springs and a stiffer AVO damper on about its lightest setting. It will probably be best that he tries both and then returns whatever he does not use.

Finally, Albervin above writes about the steering damper. I went to the trouble of designing a hydraulic one, one model of which fits to the modified steering heads and the other model fits the standard steering head. On a different thread earlier today the use of oil on the rear suspension friction dampers was discussed as friction dampers have certain limitations. Why would anyone stay with a friction damper for the steering when a compact alternative which does not go fore and aft is available?
 

Albervin

Well Known and Active Website User
VOC Member
I agree with Almost everything you say except the last bit. Not all riders need hydraulic steering damping. The leisure rider can easily make do with the original friction unit. Indeed, I have done so on my B for 50,000km on unforgiving Australian roads, both sealed and unsealed.
 

timetraveller

Well Known and Active Website User
VOC Member
Its difficult. I supplied one of the modified steering heads to a serious racer and he did not use any sort of steering damper. He was convinced that he did not need it. Then one day he got into a wobble and there after he fitted a steering damper. I once got into a tank slapper at Cadwell Park. I had a perfectly serviceable twin disc friction damper. It might as well not have been there. I was doing about 100 mph and there is enough kinetic energy with four hundred weight of bike and one and a half hundred weight of rider (those were the days) that a friction damper is not going to do anything useful. I intend no criticism of anyone if they choose to continue to use the original friction steering damper, or for that matter friction dampers anywhere.. Just do not say you have never been warned.
 

Bill Thomas

Well Known and Active Website User
VOC Member
I had to ride a standard bike a while ago, Was not happy because of what I have had in the past,
Looked at the Video later and saw I had left my helmet undone !!, Never done that before.
For £50, Not worth the chance, But Ron does not use one !.
 

Albervin

Well Known and Active Website User
VOC Member
I understand. I have an Aprilia RS250 Race Replica I ride on the road and the occasional track day. It is sublime. Those that push it to its limits fit a steering damper. I tried one and it made normal riding a pain, so I removed it. Different strokes for different folks and those in between make their choices. I will be fitting one of Norman's steering dampers on my Shadow rebuild because I have a) been thrown over the handlebars of a Series C, b) watched someone being thrown over the handlebars of a C and C) don't want to do it again.
 

oexing

Well Known and Active Website User
VOC Member
A friction damper makes for an unpleasant steering once you do it up hard enough for any friction action at all. Otherwise it has no effect at all in a critical situation - and you cannot know before it happens. So really an adjustable hydraulic damper is a joy to have, it is not felt in normal use on the road, only when parking in the garage. But when a tank slapper condition is provoked by some circumstances it does a great job at quick motions with its damping hydraulics. You´d be able to drive one-handed on any road conditions without fear of inducing a wobble or shimmy . Did the hydraulics on the fifties Horex Regina last year and liked it at once on rough roads I like most. No more vibrations in the handlebar from ripples on the road.

Vic
steering damper
 

Albervin

Well Known and Active Website User
VOC Member
And still nobody has yet explained why Brampton forks do not cause these issues. I am truly looking forward to doing direct comparisons on my B and C later this year or early next year. I have not ridden a C for any great distance for nearly 20 years. I think the last time was 2003 at the Canadian International rally.
 

oexing

Well Known and Active Website User
VOC Member
The Bramptons don´t have the geometric linkage problem at full extension like the girdraulics, one reason for the new steering head mod. So tank slappers are not expected with Bramptons. Nevertheless I´ll fit hydraulic steering dampers on them, at € 30.- no factor.

Vic
P1060214.JPG
 

MarBl

New Website User
VOC Member
Thank you for the extensive answer.
As far as I am concerned the modified steering stem seems the way to go. Surely I wont race the bike nor try to reach the ton anytime soon. But you never know when you are confronted with an emergency and in that case I'd like to have the best setup available without altering the apperance of the bike in an unfavorable manner.
May I ask where to get the springs with the unique spring constants? And should I go for an AVO Damper? The Thorntons seem to be rated the best but maybe are no longer available?
On base of my first inspection of the bike there will be quite some work to do anyway, so its best to do it the right way, if its disassembled already.
Many thanks!
 

davidd

Well Known and Active Website User
VOC Member
There has been so much discussion of this issue I don't blame anyone for having questions. I originally had this discussion with Rip Tragle on this Forum. The new FF2 will prevent a wobble, but it is a specific Vincent wobble that is really un unforced error. You cannot prevent "all" wobbles because a wobble on a motorcycle is part of the two-wheel design. Wobbles can be minimized, but not eradicated.

The wobble that could happen with the Girdraulic occurs because the axle path was designed incorrectly. It angles forward and up. The new stems change the path to either straight up and down (with a slight rearward tilt) in the case of the JE stem to rearward or "telescopic.

I did a full-size mock-up of the Brampton and the Geometry was very close to straight up and down. I did not have working Brampton at the time, but I remember deciding that the difference in Brampton geometry was why the forks were seen as a good replacement for Girdraulics. As a result, I chose a Girdraulic axle path that was closer to the Brampton, mostly because I thought that Vincent and Irving would have done so if they had realized that the Brampton geometry had been abandoned.

So, the new stem won't cure all wobbles, but it will provide handling that is very reliable and predictable.

David
 

greg brillus

Well Known and Active Website User
VOC Member
Oh dear here we go again..........Ok the big difference between the Brampton's and Girdraulics is actually nothing........yes nothing..........The later factory design was to improve on the strength and total movement of the forks......... Yes they improved the strength and yes they improved the travel........now this later point is where they went wrong........They went wrong in using longer stiff springs, this single factor changed the link geometry to a condition where the forks basically "Over center"........to prove this point and that Brampton's can suffer the wobbles, look at some video's shown on this forum where a pre war twin is loaded to the max with pannier racks and luggage, then a rider of lighter weight takes off and the front end starts to weave left and right. I bet if you could see the links, they would be pointing down at the font.........This is the exact same condition that the Girdraulic's have from their outset. Take a nice open series "D" for a spin, lovely soft compliant suspension........Ok hit a few bumps in the road surface, not overly fast say 60 kph........now apply the front brakes and look down at the upper link and watch what happens to it..........All that lovely soft suspension suddenly stops. All you've got now is the side walls in your front tire....... So lowering the front using short springs works, but the stem mod returns the full travel and you can use special springs made specifically for it.........The shock absorber is not an issue, so long as it feels fine and has not leaked out t's oil........Yes do lubricate all the spindle bushes and spring box pivots......the friction in these front ends is really very high, and this adds to the problem overall. When I ride customers bikes now with a stock front end, I am very cautious, and reminded of how potentially dangerous they can be........Well I rode one the other day that had little or no brakes, so that was a good thing............. ;)
 

oexing

Well Known and Active Website User
VOC Member
Girdraulics not being my topic, but common girder forks need not be very stiff from friction in their bushes when all is well as designed. Maintenance and line- reamed bushes provided with all correct geometries you actually need these friction discs for reducing liveliness . Friction in typical bushes is not a factor, minimal compared to what you want from hydraulic dampers on teles or rear shockers. So I would not go for ball or needle bearings in girders as much as I like them elsewhere. Instead Permaglide or IGUS bushes , no grease duties with these.

Vic
 

MartynG

Well Known and Active Website User
VOC Member
I understand. I have an Aprilia RS250 Race Replica I ride on the road and the occasional track day. It is sublime. Those that push it to its limits fit a steering damper. I tried one and it made normal riding a pain, so I removed it. Different strokes for different folks and those in between make their choices. I will be fitting one of Norman's steering dampers on my Shadow rebuild because I have a) been thrown over the handlebars of a Series C, b) watched someone being thrown over the handlebars of a C and C) don't want to do it again.
I'm with you on this Al. around 5 years back out on my Comet with original configuration girdraulics, series 'D' friction damper, Ikon front shock, just touring a country road and had a massive tank slapper. I woke up in the ambulance some 30 minutes after the event!

My Comet is now fitted with the modified steering head, thornton front shock (unfortunately Thornton are no longer in business) and a hydraulic steering damper (Kawasaki). At all times I ride with the steering damper on its stiffest setting.

With that setup I still experience the occasional mild head shake, but that's all it is - no tank slappers!

The key to this is how the two types of steering damper works.

The original friction dampers provide maximum damping when the friction pads are moving a very slow speed and as the speed of the friction pads increases (like with head shake) the damping effect becomes progressively less.

Hydraulic dampers are exactly the opposite. At low damper movement the damping effect is low but as the speed of the damper rod movement increases the damping becomes progressively heavier - exactly whats needed to control head shake and tank slappers.

Attached is my steering damper installation.
 

Attachments

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greg brillus

Well Known and Active Website User
VOC Member
The steering damper is a band aid to the problem...........personally from about 6 or so years of riding bikes with the steering mod, including a race bike........ I would feel safe running without one all together. But I still run one and would not advise anyone otherwise.
 

Bill Thomas

Well Known and Active Website User
VOC Member
Martyn, I completely under stand why you would want to run your Hydraulic as stiff as that,
But I think you are making it act like a friction damper ?
Just my thoughts !.
It depends on the gearing of yours, But on mine I run 2 clicks from soft on my Twin and my Comet.
I find it does not have to "feel" like it's doing anything, It just calm's things down.
As does Taper rollers at the bottom.
Good Luck, Bill.
 

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