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FF: Forks Modified Steering Stem


timetraveller

Well Known and Active Website User
VOC Member
If I've done the sums right then if your spring was correctly 36 lbs/inch at 16.5" long them shortening it to 16.0" will make it 37.125 lbs/inch. I regard that as within the manufacturing tolerances. Shortening or packing by fractions of an inch might be regarded as tuning for the individual. Chris Launders at 280 lbs had to pack his 45 lbs/inch spring by about half an inch. I'm more than happy to get a price for making some of those adjustable length inner spring boxes but I would need to have an order from one or two people to make it worth while bothering people.
 

macvette

Well Known and Active Website User
VOC Member
If I've done the sums right then if your spring was correctly 36 lbs/inch at 16.5" long them shortening it to 16.0" will make it 37.125 lbs/inch. I regard that as within the manufacturing tolerances. Shortening or packing by fractions of an inch might be regarded as tuning for the individual. Chris Launders at 280 lbs had to pack his 45 lbs/inch spring by about half an inch. I'm more than happy to get a price for making some of those adjustable length inner spring boxes but I would need to have an order from one or two people to make it worth while bothering people.
All other things being equal, the spring rate change is calculated as follows.
New spring rate = old spring rate x original number of coils ÷ number of coils after shortening.
The number of coils refers to active coils ignoring the flat end coils so using overall length change is not a precise way of calculating the new spring rate
 

davidd

Well Known and Active Website User
VOC Member
The load the spring will carry is determined by the diameter of the wire and the overall straight length of the wire. Even coil springs can be thought of as a torsion spring, straightened out. If you think of one end of the straight spring wire in the vise and the other end with a vise grip plier attached, you will see that for the same diameter wire a short spring wire of say, two feet, will be quite stiff to rotate with the vise grips. On the other hand a straight spring wire of ten feet will rotate quite readily.

The Vincent springs has many coils, so it is quickly identified as a "soft spring" because it would be quite long if it were straightened out. Every little bit you cut off will make it a little bit stiffer. Generally, if a 36 lb/in spring is 16.5" or 16" is is still 36 lbs/in. The springs just have differing heights (differing spacings of the coils) and both have the same length of straight wire.

Technically, you have to "set" the spring once you get it from the manufacturer. Setting is the act of compressing the spring until coil bind occurs. It will often make the height of the springs more consistent.

Typically, the fewer coils a spring has the stiffer it will be for the same wire diameter. If you count all the coils you may need to subtract 1.5 coils to arrive at the "active" number of coils. Thus, each end of the coil spring that is flattened and ground is not counted as an active coil for 3/4 of its length (this formula may vary a bit). Any coils that are close enough to touch each other after a very small amount of movement will become inactive after they touch and bump up the stiffness of the spring.

David
 

timetraveller

Well Known and Active Website User
VOC Member
OK Chaps, always one to learn from others and so thanks for the help and advice. However, I suspect that with a long spring like the front suspension ones, as opposed, say to a valve spring the difference will not be very great. In the search for accuracy I have just counted the number of coils in one of the 36 lbs/inch springs and there are 52. Removing three from this figure as advised above to take into account the flattened end coils gives 49. Half an inch of shortening means removing about three coils so using the above calculation means that (49/46) x 36 gives 38.3 lbs/inch. My crude calculation gave 37.125. Near enough I would have thought.
 

vibrac

Well Known and Active Website User
VOC Member
Not wishing to further complicate matters :p but I suppose that after 70 years and thousands of owners I am not the first to notice that Vincent inner valve springs fit smoothly into upper spring boxeso_O broom handles are not the only way!
 

Bill Thomas

Well Known and Active Website User
VOC Member
If you cut one down, It can go inside a standard front shocker !, To give a bit more bounce for my comet forks.
Cheers Bill.
 

timetraveller

Well Known and Active Website User
VOC Member
I just had a call from Robin Stafford who fitted one of the JE steering kits some months ago. I originally supplied him with 36 lbs/inch springs for his twin as with his weight I thought that they would be about right. Robin found them too strong and so I sent him some 33 lbs/inch springs. He found these much more comfortable but under heavy braking the front end dipped more than he liked. His solution has been to fit some original Vincent inner front springs. These were cut down in length so that they only come into play after about 1.25" to 1.5" of movement. He finds this has cured the problem and effectively gives him a two rate spring. Note that earlier Gary Gittleson shortened his 36 lbs/inch springs by about half an inch. These two examples are the kind of feedback that allows or encourages users to try to tune for their own use.

On a different front I am having trouble finding some thin wall stainless steel tube to allow the tuneable inner spring boxes as required by Comet Rider, a few posts earlier. If there is anyone out there who can offer advice then it will be gratefully received.
 

bmetcalf

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VOC Member
I tried about six different super-duper glues and none of them kept the piece of radiator hose on for more than one try. I finally got around to having 1/4" thick steel pads welded to the feet of the stand. The report is that it works well now.

With the longer eyebolts, I find that my Hills centerstand leaves both tires touching the floor. I'll write to him to let him know. His request for measurements when ordering would account for that. I guess 1/4" thick wear pads welded on the feet would be enough, but that is easy enough to check.

Dave Hills sent me these thoughts in response to my question:

" You are of course not the first one who has altered the suspension on his bike and then found that the stand is too short. I have seen several ‘mods’ to the stand to achieve a slightly greater leg-length. One idea-probably the easiest one is to cut a section of hard rubber from either a tyre or an old rubber boot and use something like “Gorilla Glue” to stick this to the sole of the feet. A 3/16” thick piece of rubber is probably all you need. An added advantage to this ‘mod’ is that it gives the bike a lot more grip especially when parking on steel plates as encountered on cross channel ferries .But I guess that you are unlikely to do this living in USA but a frequent journey for us living on a little island.
Another idea is to drill and tap the feet up into the hollow leg and then screw in a extra large headed bolt. Quick and easy but not such a good idea if you park on wooden boards or ‘posh’ tiles.
Probably the best way to get a bit more leg length is to carefully cut off the ‘heel & toe’ of both feet, then round up the ‘stump then weld on a pair of new feet. Using ¼” plate this will give you about 7/16” more ‘lift’ at the back wheel. Do remember that by increasing the leg length by ¼” lifts the rear wheel by about 3/8” or more. A good way of calculating the exact amount of increase you need is to slide thin pieces of plywood under the legs before you start altering things. Using thin plywood you can get the ideal height that suits you and then measure the plywood to get the increase you need."
 

Gary Gittleson

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VOC Member
Finally, I have been able to give this setup a reasonable trial. It's as good as what others are saying. Besides the primary purpose of dramatically reducing the ever-looming threat that the original design presents, this mod improves the overall road-worthiness of the Girdraulic fork. Anyone who does now or plans to ride a Girdraulic-fitted Vincent rather than store it behind glass, should give this mod serious consideration.

The roads around here are pretty rough after a hard winter. There was plenty of opportunity to see how she'd handle the bumps. As others with this mod have observed, the freedom of movement of the forks is amazing. If I didn't have an LED headlight bulb, I'd be thinking about suspending the headlight for fear of breaking a filament. It was in constant motion, with hardly any of that transferred to the handlebars. I also noticed a considerable improvement in cornering. It tracks smoothly and predictably and drops into the turns much more freely. That latter point I assume is due to a reduction in trail. I believe that the stock setup has a lot of trail over much of the path of axle movement. It also has the unfortunate feature of varying the trail considerably depending on the degree of compression or extension. In an case, I always thought that the stock setup gives a battleship-like response to the initiation of a turn. No longer.

I will have to take the words of the experts in regards to the increase in safety. I have no desire to put this to the test. The other benefits alone make this job worth the work and expense, both of which are well within reason.

There are a few options that Norman offers with this kit. I chose to retain my Thornton shock, to include the ball-bearings for the lower link and the hydraulic steering damper. The latter item by the way, works very nicely and I have set it toward the stiff end without experiencing any low-speed wondering.

Norman mentioned earlier in this thread that I had cut the springs down by 1/2". To check the result of this, I placed a cable tie high up on the damper rod (a Thornton) before the ride. After the ride, rests about 1/4" from the rubber bump stop at the bottom. I am thinking of adding a 1/4" spacer atop each spring. I have some nylon washers of that exact size. So I do have two questions for Norman. Should I do this, and would that material be appropriate? If I do, maybe I should put a steel washer between the spring and the nylon to prevent the spring from mauling it.

P.S. Three cheers for John Emmanuel, Norman Walker and the several others who added much time and expertise to this project.
 

timetraveller

Well Known and Active Website User
VOC Member
Thanks to Gary for his kind comments. Regarding packing with a nylon washer; there are different grades of nylon so I cannot be sure that the one which Gary has access to will last. It would certainly do for a test and probably a steel washer between the nylon and the spring itself would help. This leads to an interesting matter regarding pre-load and spring rate. Gary removed half an inch from each spring which is the equivalent of removing one inch from one, i.e. 36 lbs of pre-load. The pre-load with the full length 36 lbs/inch springs is 216 lbs so a reduction of 36 lbs is 16%. Removing half of the one inch spring length reduction is going to reduce that to 8%. That kind of adjustability is why I designed the adjustable length inner spring box but, as above, I have still failed to find a supplier of the correct tube. I wanted to use stainless steel and at the GCM I asked Ian Savage who it is that supplies the Club Shop with these items. It turns out that it is Colin Taylor, who lives in Italy, probably uses metric tubing and who's name is not in the Confidential Admin List. I guess he is not a member. At the moment the best that I can come up with is to buy tube with the correct inner diameter, just over one inch, and then cylindrically grind the outer down to the correct size. I can find people to do that but there really ought to be an easier way.
Remember, it is only by this kind of feedback that the system can be improved so thanks to all who have provided feed back.
 

Dave61

Well Known and Active Website User
VOC Member
Thanks to Gary for his kind comments. Regarding packing with a nylon washer; there are different grades of nylon so I cannot be sure that the one which Gary has access to will last. It would certainly do for a test and probably a steel washer between the nylon and the spring itself would help. This leads to an interesting matter regarding pre-load and spring rate. Gary removed half an inch from each spring which is the equivalent of removing one inch from one, i.e. 36 lbs of pre-load. The pre-load with the full length 36 lbs/inch springs is 216 lbs so a reduction of 36 lbs is 16%. Removing half of the one inch spring length reduction is going to reduce that to 8%. That kind of adjustability is why I designed the adjustable length inner spring box but, as above, I have still failed to find a supplier of the correct tube. I wanted to use stainless steel and at the GCM I asked Ian Savage who it is that supplies the Club Shop with these items. It turns out that it is Colin Taylor, who lives in Italy, probably uses metric tubing and who's name is not in the Confidential Admin List. I guess he is not a member. At the moment the best that I can come up with is to buy tube with the correct inner diameter, just over one inch, and then cylindrically grind the outer down to the correct size. I can find people to do that but there really ought to be an easier way.
Remember, it is only by this kind of feedback that the system can be improved so thanks to all who have provided feed back.
Hi Norman,
I made new lower spring boxes using a couple of end fittings that Dave Hills kindly supplied me.
I had a real struggle to find Imperial size tube so ended up using thin walled metric tube that was very close to original size.
Cheers
Dave
 

vibrac

Well Known and Active Website User
VOC Member
Thanks to Gary for his kind comments. Regarding packing with a nylon washer; there are different grades of nylon so I cannot be sure that the one which Gary has access to will last. It would certainly do for a test and probably a steel washer between the nylon and the spring itself would help. This leads to an interesting matter regarding pre-load and spring rate. Gary removed half an inch from each spring which is the equivalent of removing one inch from one, i.e. 36 lbs of pre-load. The pre-load with the full length 36 lbs/inch springs is 216 lbs so a reduction of 36 lbs is 16%. Removing half of the one inch spring length reduction is going to reduce that to 8%. That kind of adjustability is why I designed the adjustable length inner spring box but, as above, I have still failed to find a supplier of the correct tube. I wanted to use stainless steel and at the GCM I asked Ian Savage who it is that supplies the Club Shop with these items. It turns out that it is Colin Taylor, who lives in Italy, probably uses metric tubing and who's name is not in the Confidential Admin List. I guess he is not a member. At the moment the best that I can come up with is to buy tube with the correct inner diameter, just over one inch, and then cylindrically grind the outer down to the correct size. I can find people to do that but there really ought to be an easier way.
Remember, it is only by this kind of feedback that the system can be improved so thanks to all who have provided feed back.
Nice to know in the feedback if its a twin or a comet (and perhaps the riders weight?) soon I hope to get back to sorting my comet from the ground up talking over the winter it would seem the first culprit of my rsultant solid conversion is the too stiff new AVO damper.
 

timetraveller

Well Known and Active Website User
VOC Member
Gary's bike is a twin and, from memory, his weight is about 180 lbs. He will correct that if it is wrong. On your (vibrac's) Comet I would try a short run over a bumpy road without a damper. If that works, and it should only take minutes, then we can sort out the damper.
 

Gary Gittleson

Well Known and Active Website User
VOC Member
Yes, it is a twin. It's a D Rapide. I probably weigh about 180 lbs fully geared up.
The nylon I mentioned seems quite hard. I'll give it a try. My homemade spring compressor makes the job quite easy, so I don't mind doing it a few times.

Gary
 

andrew peters

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..
 

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