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FF: Forks Modified Steering Stem


timetraveller

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VOC Member
Thanks to Andrew for his kind comments and the feedback. This helps other riders to optimise the combination of dampers and springs which will give them the best results. On that front I recently heard from Robin Stafford who rides a twin. He weighs about 13 stones (182 lbs, 83 kgs). I thought that the 36 lbs/inch springs and the normal AVO front damper might be the best combination for him but he found it too stiff. I therefore sent him a pair of 33 lbs/inch springs which he found just marginally too soft. His experimental solution was to take a pair of the original small diameter Vincent inner springs and cut them down in length so that they only came into play when the forks had been compressed about 1.5 inches (3.8 mm). He finds this to be a very comfortable and well handling combination. The softer springs respond quickly and easily to small bumps or road imperfections but with large holes, traffic calming bumps or heavy braking the stiffer springs come into play and imperceptibly take up the strain. I have checked with the spring manufacturers and there would be no problem making some of these and they would be wound in the opposite direction to the outers to avoid coil binding. As Robin shortened his springs the spring rate will now have gone up so it would be good to find out what the spring rate is now.
 

Black Flash

Well Known and Active Website User
VOC Member
I have received Norman's kit two years ago but didn't have time to finish the Comet due to work.
At the moment I am doing many short laps trying to get the mikuni in as good as possible state of tune.
First thing that I noticed was rolling down my drive way and breaking, the front dived, something completely new to me.
On my test road I need to pass two sleeping police men.
I did that with various speeds and there are also patches where the tarmac breaks up.
The sleeping policeman when passed too fast [somebody with common sense would never pass them at that speed] will bottom out the forks.
Contrary on the breaking up patches the bike is super smooth at any rate of speed, far better than before.
Going round corners the bike behaves very good, just as she should. I can't feel any difference there. At the moment the bike is not registered, so my test rides are mainly on quiet back roads of degrading tarmac surface. There is certainly a noticeable gain in comfort on that type of road but speeds are limited due to condition to about 50 mph.
I am really looking forward to get the bike registered and do my usual lap [around 50 miles] on proper roads, I will keep you informed once I have done that.
Bernd
 

Dave61

Well Known and Active Website User
VOC Member
A few months back I bought the complete kit, with bearings for the lower link and Norman’s steering damper.. I also put in new steering head balls and cups. It took a while to complete the work on my Rapide but I’ve been doing a lot of other things on the bike preparing the bike to be ridden a lot.. I have rebuilt both wheels with new bearings and fitted a pair of disc brakes on the front. (See thread on disc brakes on a C) I also reprofiled the front fender and made a new bracket and new support struts, this was partly in case the fender hit the exhaust and engine now the fork moved in a different arc but I never really liked the way the fender sat so high with the 19” wheel, the clearance under the fender made me think it looked like a dirt bike...
Back to the steering head mod.. originally Norman had suggested 45 lb springs and a heavy AVO damper but when I got the bike on wheels it was obvious to me that the fork was going to be too firm and uncomfortable, not Norman’s fault really, I had told him I would like the fork to be firm as I would be 2 up with luggage much of the time.. however, as we’ve read on this thread, much has changed in the way of opinions and experience.. as soon as I told Norman I found I may want softer springs and damper he had new parts winging their way to me.. Thank you Norman for that!
This is my resulting set up:
My weight 210lb wife 150lb (ish.. I guess?) saddle bags and rack for big bag.
36lb springs, no modifications at all
AVO damper, normal. minimum setting
Norman’s hydraulic steering damper set 7 clicks (I did find I needed to modify the arm to clearance the engine, but Norman now specifies this)
Ball bearing lower link
Ball race steering head
AVO coil over rear shock, a lot of preload (for this trip) and damping about half way
19” wheels on Roadriders
Powerful twin discs...
one other modification I found necessary, although probably peculiar to my bike, I had to fit slightly higher wider handlebars as the new fork action meant the top link could come into contact with my brake master cylinder.. I’m content with the new riding position although I really liked the Vincent flat narrow bar.
I had the bike ready just in time for my trip to The Quail in California, I took the bike around the block and packed on the luggage for the first ferry from Victoria in the morning.. Was I prepared for my first long trip on a freshly built bike? Was I sure I had the suspension set up satisfactory? Well time was up, I was as prepared as I could be.. I had gone through everything more than once, I had read and re read the forum threads etc.. I was satisfied and confident, at least l knew the bike was as good as I could get it..
2800 miles later I have to say a big thank you to Norman for his help, also to the many posters that chipped in with useful tips and advice, even if sometimes it was heavy, technical and maybe a little bit over thought out. (gulp)
So my experience with the steering head mod could be just luck, it worked for me right out of the box. I will pass on this tip though, careful assembly! Mainly the pivot bolts and lock pad bolts, over tightening will cause stiff action and although it’s obvious now I’m saving it if you just tighten everything up it doesn’t work properly, if it’s loose then your steering and suspension will feel ‘loose’
I know I still have some riding to do with less weight on the bike and maybe I’ll want to modify or adjust things.. so far though I’m very happy with the handling and comfort, easily as good as my BMW R90S that I’ve been riding for 40 years! The Vincent tracks straight and corners smoothly with no weaves or wobbles at all.. I’m sure the steering mod is essential with a more powerful brake although I admit I have no experience of a bad handling or poorly brakedVincent.. why would anyone put up with that? Haha
So thanks again Norman, of course John Emmanuel for the development, and you guys for your input and encouragement.. I will continue to try to improve my Vincent and I guarantee to keep riding the bloody thing..
Really good write up Andrew, your bike certainly looks good & more importantly works well.
Hope to have mine on the road this year & give my feedback,.
Cheers
Dave
 

timetraveller

Well Known and Active Website User
VOC Member
Bernd, once you have had more chance to try it then perhaps the same idea as Robin has used, fitting a short inner spring, might be what is needed. The overall length of the 36, 33 and 30 lbs/inch springs is 16.5" (419mm). They are all installed with a length of 13.5" (343 mm) so for the smaller diameter springs to come into use after 1.5" (38 mm) of movement the new springs would have to be about (343-38=305mm). This way one might get the advantage of the easy movement over small bumps but prevent the bottoming out over large bumps. Does any one know the length and spring rate of the original inner springs. If we have that then I can work out what rate the new springs would have to be to get the same effect as Robin.
 

andrew peters

Website User
VOC Member
Bernd, once you have had more chance to try it then perhaps the same idea as Robin has used, fitting a short inner spring, might be what is needed. The overall length of the 36, 33 and 30 lbs/inch springs is 16.5" (419mm). They are all installed with a length of 13.5" (343 mm) so for the smaller diameter springs to come into use after 1.5" (38 mm) of movement the new springs would have to be about (343-38=305mm). This way one might get the advantage of the easy movement over small bumps but prevent the bottoming out over large bumps. Does any one know the length and spring rate of the original inner springs. If we have that then I can work out what rate the new springs would have to be to get the same effect as Robin.
The cut down inner spring is definitely something I’ve considered, it makes sense to have some sort of anti bottoming spring, almost gives the fork a progressive rate, I think coil bind should not be an issue unless the springs are a tight fit inside one another.. hopefully the short spring isn’t going to rattle around inside the tube as it’s not under tension most of the time.. I still have to experience the fork action in a ‘normal’ riding attitude, when the bike has been loaded up I’ve avoided bad roads (except San Francisco!) I’ve also avoided deliberate bumps and very hard braking (except the blind woman in the Mercedes turning in front of me in San Jose.. there’s a pattern here, avoid riding in California?) in the next few weeks I may try a few different experiments just to test the suspension, ‘course the trick is to ride on the edge of braking something or falling off! So my testing will be sensible, if I wanted perfection I wouldn’t be riding an old bike would I (I also tolerate a 66 year old truck as to me it seems to do as good as a new truck, it hauls stuff and doesn’t break down)
 

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davidd

Well Known and Active Website User
VOC Member
Does any one know the length and spring rate of the original inner springs.
9.5 Lbs. per inch for the inner spring. I have the free length as 15.3".

it makes sense to have some sort of anti bottoming spring, almost gives the fork a progressive rate, I think coil bind should not be an issue unless the springs are a tight fit inside one another.. hopefully the short spring isn’t going to rattle around inside the tube as it’s not under tension most of the time..
I used inner reverse wound springs on the rear. They were short and worked on the same principle that you are shooting for. The spring manufacturer can design them to work well in the outer spring without any rattling. I stopped working on the rear springs around 2002 because I decided to go with a coil overs. I did look at using progressive springs on the front and also short die springs. The big impediment was that the spring had to hold up you and the bike at the right pre load, say 200 lbs./in, which uses up an inch of travel and then within the remaining 2" hit 600 lbs. to prevent bottoming out. It turns out that it really cannot be done well either by a straight rate spring or a progressive spring. (It is a little easier on the rear due to the small amount of extra travel.)

I was unable to find a good spring rate for the stock springs. My short springs work well on the street and track, but all the spring rates seem to be too soft or too harsh and it is hard to find a sweet spot. Thus, I went the same way I did on the rear and turned to a front coil over. The front coil over seems easier to adjust for good springing. I think this is due to the motion ratio of the lower link mount and the angle correction factor of the shock, but it is a little above my pay grade.

I certainly hope that a good rate for the stock spring boxes can be found.

David
 

timetraveller

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VOC Member
Thanks for that David. Using Robin's values for how much he chopped off the spring I make it that the spring rate would have been increased to about 12 lbs/inch by shortening the 15.3" spring to 12.0". If the interest is there then I could order a batch of these. Let us see what happens.
I also got an email last night from the first person the fit one of the newly designed hydraulic steering dampers to his standard twin front end. He is Andy Hopkins from Dorset and he writes:-

I fitted the damper today. Most difficult part was getting the tap to start in line with the hole. With forks attached I could not use tap holder so used a square drive universal socket. One of the metal plates plus two friction rings filled the gap. So far I have ridden it about 3 clicks from lowest setting. For the 1st time in 20 yrs i rode hands off without a hint of wobble. Before, if I released my hands from bars it would start to wobble . Replacing a hand on bar instantly stopped it. I have Touring model with 19 x 3.50 and 18 x 4.00 rear tyres. Initially Avon Speedmasters but now Roadrunners.
Regarding your damper settings. From 1 to 23 what 'click' do you use ?
Thanks for a great product. How do I find a replacement damper when it wears out ?


Four are now out there with another one to be delivered on Saturday so let us see how the feedback on these goes.
 

Chris Launders

Well Known and Active Website User
VOC Member
Did any of our modified steering stem users attend the international rally, it seems to me this would have been an ideal concentrated test of the system, comments anyone who did ?
Chris.
 

timetraveller

Well Known and Active Website User
VOC Member
Hi Chris, I don't know about this year but last years rally in France was a big test for the system on Chris and Tracy Tilley's twin. I had originally supplied the 45 lbs/inch springs and the stiffer damper. These were much too stiff and were changed to 36 lbs/inch springs and the standard AVO damper. They used the system on everything from motorways to unmade roads and went from Wales to the Pyrenees and back and were very pleased with all aspects of the comfort/handling of the front end. If they see this then they will probably provide extra information.
 

bmetcalf

Well Known and Active Website User
VOC Member
There were two bikes with “concentrics”, but I didn’t ask either rider about them. One bike had footrests beveled like Peter Volkers’, or is it the other way around?
 

hrdaustria

Well Known and Active Website User
VOC Member
There were two bikes with “concentrics”, but I didn’t ask either rider about them. One bike had footrests beveled like Peter Volkers’, or is it the other way around?
good morning,
the bike is mine, used quite a lot on our alpine roads and fairly quick too.
i had troubles with the springs being to stiff for my weigth. just in front if the second stage of the international i fitted the 32 lbs/inch springs from norman as the 36 ones toped out to often. i´m still using my thornton front damper as i found the special avo even in the softest setting to stiff for me. i have not yet tested the 32 springs in combination with the avo damper. i´ve the hydraulic steering damper in use too. the only difference is that i altered the fittings to use needle roller bearings instead of the smal ball bearings.
the handling of the bike is good, a little more comfort to ride compared to my old setup with the thornton and justin mackay-smith´s springs. never experianced a front wobble with this setup.
on quick cornering on rough roadsurface the fork is acting lifelier.
braking has improved as the movement of the fork during braking seems less restrictive now.
michi
 

greg brillus

Well Known and Active Website User
VOC Member
The 36 Ib springs top out because they are too long............. You need to shorten them by small amounts until the "Topping out" does not happen. I have found that the softer springs are too soft even on a Comet, the Thornton shockers are by far the best.........Use a pair of 45 Ib springs with about 20 to 25 mm cut off each and this will be perfect. I'm still installing these kits for folk here down under and getting only positive results.
 

greg brillus

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VOC Member
All the bikes I do including singles and twins same 45 Lb springs, only I remove slightly more or less off the length of the springs to suit heavy or light weight riders. The twins will handle a stiffer shocker but the singles need a softer one. The last single I did the rider was about the same weight as me, and I installed an original Armstrong shock, but he felt it was almost too soft, and replaced it with a Thornton he had. Again this was with a pair of the 45 Lb springs with about 25 mm cut off one end on both springs.
 

timetraveller

Well Known and Active Website User
VOC Member
Greg, a question, which if I have asked before I apologise. If you put a cable tie round the inner front spring box, push it up against the bottom of the outer spring box and then go out for a ride over bumpy roads what movement is recorded by the shift in the cable tie. With the set up used here we get about three inches or possibly a little more. That is the limit of the movement controlled by the AVO dampers. There are two thing to consider, the pre-load and the spring rate. The pre-load has to be right to ensure the geometry is working as it should (lower link more or less horizontal with the rider seated) and I try to get as much movement as possible without the system bottoming out.
 

greg brillus

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VOC Member
It generally uses most of the travel left in the spring cases.......I have only ever chopped about 15 to 20 mm off one machines cases, the lower halves where like a knife edge at the top and jamming on full compression. All other bikes I have left the cases untouched, although I do go to a lot of trouble to make sure they do not bind or jam when fully compressed. I have tried pretty much all springs and shocker combinations........ If you install the springs as they are, the front end will be topped out, there is too much pre-load........... So once the springs are shortened enough for this not to happen, then the front end will easily bottom out on heavy bumps and braking. If people are using the weaker springs, and are happy with the results, that's great, but I will say that it is definitely the shock absorber that is taking up a lot of the load. If you disconnect the front shock absorber and ride the bike, it will readily bottom out without much of a bump and applying the front brakes. The singles will definitely feel softer and better rider comfort than the twins on account of the extra 30 Kg's in weight...........I tried using softer springs on mine and it did feel softer, but would bottom quite easily. Perhaps if I chopped some of the cases down it might handle the softer springs, but I really don't want to do that .........I'm very happy with my bike..........It is at the rear of the bike that the bigger gain would be made to ride comfort, say a fully sprung seat, but I'm still working on that one ........Lets not forget that the main gain from this change to the front end was safety first ........The handling and braking are also significantly improved .......These are the most common comments I get from riders who I have helped out with this mod.
 

Black Flash

Well Known and Active Website User
VOC Member
Just a short update,

As you probably know I am testing my new 8" 4ls brake at the moment.
Yesterday I had a very spirited ride about 50 miles long. Loads of corners, different road surfaces ranging from being great to rubbish.
I have a fully sprung seat and Thornton suspension fitted to my go faster Comet.
The gain in comfort is something that I never expected. As I was using the brake a lot to bed in the shoes I suddenly recognised how much the forks are moving now. Also going over ripples, the road holding and comfort are excellent.
Broken tarmac with 1 inch deep flat bottom potholes in series, no problem at any rate of speed. Same situation going round corners with a good lean at 40 to 70 miles, no fear, no wobbles, great road holding.
It is long ago I rode that kind of roads the same way on a standard Comet with standard dampers and I am sure tthe dampers also make a big difference, but this ride yesterday was great and it gave me full confidence in the bikes behaviour. To put it in simple words the bike feels more modern and safer now.
By the way I was pushing the bike through all these corners without any steering damper fitted, I had to make a new bracket to fit the damper but as the weather was great, I preferred to go out for a ride and give it some beans.

Bernd
 

timetraveller

Well Known and Active Website User
VOC Member
I have recently received an order for six new steel steering heads. Then, on Saturday, I got another order for another steel one and then yesterday for one aluminium one. This is more than I have left of the steel ones and there are only three ali ones left after this one goes. My intention was to supply those with the ali head lugs which are under way. This means that there are non left for me. I do not mind getting another batch of ten made and having a few left on the shelf but do not want ten sitting there with a total cost of nearly £3,000. Is there anyone else out there who is likely to be wanting one? If so please let me know.
 

erik

Well Known and Active Website User
VOC Member
I have fitted the mod. st. stem to my rapide .32 lbs springs and no inner spring.A new damper from the voc sp. comp. fitted. real sive ride with lots of comfort.Better roudholding than my standart comet.I would recommend it .Thinking about an Hydraulik steering damper.regards Erik
 

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