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FF: Forks Modified Steering Stem


snm1965

New 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.

I expect I might be too late; but yes I will have steel one please.

I have also e mailed you.

Simon Meikle
 
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b'knighted

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VOC Member
With the weather finally reaching the point where tools don’t freeze to my fingers, I’m finally getting around to changing my headstem. I bought the front kit with springs and AVO damper. The Comet the kit is going on has been running with a soft and bouncy Laney Thornton setup front and rear. There were some reports of the AVO being a bit too stiff.
Would those of you who are using the Concentric/AVO kit recommend that I fit the whole kit or initially just change the headstem and bottom link to keep the springing and damping that I been using?

I believe there was a suggestion of running the AVO in on the rear?
 
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vibrac

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VOC Member
My stem is fitted to the racer and it does feel stiff however it's going to be a long wait for a racetrack this year....
 

BigEd

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VOC Member
VOC Forum Moderator
b'knighted said> Would those of you who are using the Concentric/AVO kit recommend that I fit the whole kit or initially just change the headstem and bottom link to keep the springing and damping that I been using?
I've been experimenting with various spring combinations and haven't quite settled on a final setup. It depends on what springs you plan to use. I think my probable spring choice will be 45lb springs from Norman shortened by approx 1 inch. (I think Greg suggested that this was OK on several conversions he had done and would be a good starting point.) On a Comet a lighter spring might work better, Norman has/had 33lb springs as well. I use an AVO damper front usually set to give quite light damping. (AVO monoshock rear.) If you get topping out, more damping can help but here your choice of spring rate comes in too.
I would go ahead and fit the new head stem. You can then just carefully try it around the block with the bits you've got to see which direction to go with your settings.
With the head stem fitted and forks back in place, it is then a relatively easy job to change the damper or springs. (I've got quite quick at removing an refitting the front spring units through lots of recent practice. ;) )
 

Chris Launders

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VOC Member
I would try it first with the springs you have, then fit the springs Norman has sent, the riders weight makes a big difference to what springs are required (on my twin I have 45lb/in springs and 11mm packers as I weigh 20 st, others manage with much softer springs on theirs), don't forget you can always mix springs, also shortening springs lowers the static height but stiffens the springs.
 

timetraveller

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VOC Member
OK Chaps, I will try to put all this in context. For historical purposes only, remember that all this started when John Emmanuel showed me his conversion to the front suspension and I finally understood what he had done. Having had a serious speed wobble during my racing days I appreciated the benefit of what he had done and it is entirely to John's credit that he gave me permission to copy what he had done. I think that the first batch was only five or ten and they sold quickly. Chris Launders was one of the first purchasers and very good at both testing and providing feedback. Originally the suspension worked well for Chris with 36 lbs/inch springs with three inches of pre-load. However, Greg Brillus then came up with the idea of fitting two ball race bearings to each side of the lower link and Chris then fitted a needle roller bearing to each side in order to similarly reduce the friction. The results were startling. At the start Chris thought that the damper (AVO) had failed and it was clear that the springs were not strong enough. Remember, the only thing changed was the reduction in friction at the rear of the lower link. After various tests and calculations I came up with a change to 45 lbs/inch springs with two inches of pre-load and AVO produced a stiffer model of damper. At that stage I had not realised just how sensitive the system was to weight differences. It slowly became clear that there is a lot of weight at the front end which is un-sprung. This includes the wheel, brakes, forks, mudguard, headlight, various stays and probably a Shadow clock. Somewhere about 70 to 80 lbs. It also became clear that weight on the back, rear wheel, pillion passenger, luggage, seat etc. did not affect the suspension at the front. Therefore is was both the riders weight and whether the engine was a twin or a single which was being sprung and therefore subject to most changes. Until this became clear to me I supplied the 45 lbs/inch springs and the stiffer damper to all those who had twins in full road use trim. Stripped down racers were already being supplied with weaker springs and the original spec. AVO dampers. Slowly, feedback from several users in the UK and Europe allowed me to home in on what seems to be a typical specification. It should be noted here that Greg Brillus in Australia prefers stiffer springs, typically the 45s, even on Comets if I have that right, and softer damping. A lot of feedback over here prefers the softer springs and the variabl/tunable damping of the AVO. One further piece of information before I get to answering the question in posting 1,162 above. Robin Stafford has come up with a useful idea which others might benefit from. Robin's bike is a twin and Robin himself is one of the lighter weight riders. On his bike he liked the soft and compliant effect of the weaker springs but occasionally would bottom out over serious potholes. He came up with the idea of putting one of the original Vincent inner front springs inside the new spring and I did the calculation as to what length they should be installed at. Remember that the 30, 33 and 36 lbs/inch springs are all intended to be installed with three inches of pre-load and they are all 16.5" long. This means that their installed length is 13.5" and after three inches of movement they are then only 10.5 inches long. I suggested to Robin that he should try to make the length of the springs such that they only come into play after about half of the three inches of movement but after quite a lot of use. He now thinks that it might have been better to have them come into play after only one inch of movement. On the other hand he is really pleased with the compliant nature of the suspension and how it soaks up the bumps and ripples over typical road surfaces. So, being prepared to think and experiment can help to get the system near to each individuals requirements.

Now back to the question; the dampers are fine and the problem was with my original impression that all the twins would need the stiffer dampers. It turns out that the spec. worked out between AVO and Hadronuk is suitable for most riders but for those in the 18 stone/252 lbs/114 kg, and upwards range you will need the 45 lbs/inch springs and the stiffer damper. You might even need stiffer springs. I have exchanged all the stiffer dampers for those who found them too stiff or the owners have had AVO convert them back to the original spec. The number stamped on the damper ends in a 7 for the originals and an 8 for the stiffer ones. There is nothing to be gained by running a front damper on the rear. Damper technology has moved on a lot in the last fifty years. You have the springs supplied with the kit. They are designed to go with the rest of the system. I do not have the spec of the Thornton springs but it is unlikely that they will be optimum. I can't remember what springs you have but I would suspect that 33 lbs/inch would be about right if you are going to use low friction bearing in the rear of the lower link. If you find these unsuitable then there is no charge for changing them to stiffer or softer springs, assuming that they are still in good order, apart from postage. If you are going to continue to use the Oilite bushes then your feedback would be welcome.
Also, please remember, that there is now a hydraulic steering damper kit designed to fit to the new steering heads.
 

greg brillus

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VOC Member
Interesting findings........Cath and I have just completed a 10 day rally through Tasmania with a group of many other mostly Brit bikes. Fabulous country for bike riding, and just about as much riding pleasure you could hope for. The bike performed very well, and the suspension was great.......On some very harsh bumps it did feel as though the suspension bottomed out, but the front will readily top out as well. I can't see any visual signs of damage from the cases on the front running out of travel. I had also made up a new "Rear suspension" to replace the rigid seat stays, this on account of the "jarring through the back" that Cath had complained about many times.......This mod worked out extremely well, and her feedback was totally positive. I have considered making others but the cost is probably a bit high.......I have not been able to install any of these kits and springs without having to cut the springs down some........When trying to assemble them as they come, the front end is "Topped out" and I cannot push down on the bars to budge some movement from the forks at all, so I am interested to know how others do it let alone adding packers under as well. No suspension that I know of is topped out at rest, so this is something I am struggling with, anyway if it works for others then that is fine. After the Tassie rally I have interest in about 3 more kits.........will it ever end, I wonder.
 

greg brillus

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I'm hopeless at pics, but I'll get the better half to help me put some on here....... It is something I've wanted to do for some time, as the route of the fully sprung seat is practical, but looks ugly in my opinion. The "vacant" seat stay brackets left in the cold on the rear frame looks out of place....... I wanted to replicate the ones that Harry Belleville or whoever it was, that did something similar years ago, but make them look more like a factory made item using modern technology. The dozen or so other Vincent riders on the rally were most impressed.......even the non Vincent riders...........:).
 

timetraveller

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VOC Member
There are several things i do not understand about this mod. For example on some bikes it is necessary to take up to about 6 mm from the rear/bottom of the top link to clear the AVO damper while on others it clears. On some bikes the front mudguard can hit the front cylinder, on others, plenty of clearance. Greg finds that lots of the bikes can have the suspension 'topped out' and yet one of the criteria for setting it up is to watch it settle about half an inch when one sits on the bike so that the lower link is just about horizontal. If one sits on the bike and nothing moves then it is certain that the front springs are too strong or too long. Greg seems not to have to shorten both inner and outer front spring boxes whereas most users find that without that one does not get the full movement. One user reports that he is getting 3.75" of movement on his spring boxes but he is not using the AVO damper. Greg reports that he can get both topping out and bottoming out on rough roads. Does that mean that a stiffer damper should be used? So many questions, so little time :confused:
 

TouringComet

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VOC Member
VOC Forum Administrator
It is something I've wanted to do for some time, as the route of the fully sprung seat is practical, but looks ugly in my opinion. The "vacant" seat stay brackets left in the cold on the rear frame looks out of place....... I wanted to replicate the ones that Harry Belleville or whoever it was, that did something similar years ago, but make them look more like a factory made item using modern technology.
If you are referring to the seat stays with the built in shock absorber, I believe Gene Aucott made them.
 

oexing

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VOC Member
There are a few items in this topic to be discussed separately: Any bad excessive "friction" in original oilite bushed girder links is most likely due to poor alignment of bushes, not perfectly line-reamed. So when changing for ball or needle bearings this defect got glossed over or rectified and was not a real snag of plain bushes. Some friction in there is basically no factor as any shock absorber has a LOT more friction in it than that tiny amount in a plain bearing. And in most girder forks you get extra friction dampers as standard for sure . So I would not want ballbearings in there but get maintenance free bushes instead, no grease used and no rust problem on stainless bolts with their bushes.
As to topping or bottoming out nothing will help but having some rubber bump stops in suitable places when not getting real progressive springs or a combo of springs for same effect instead. Some dampers have a strong short spring inside and a rubber buffer on the external damper rod for bump stops. In modern teleforks you can add air pressure for fine tuning to suit different loads, same can be done with dampers. So maybe this could be kept in mind for mods ?

Vic
 

greg brillus

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It is possible that the bearing pockets differ from bike to bike, perhaps from previous front end damage/repair. One way I have found this could be true is on some bikes the top stem nut bottoms out on the inside before the nut tightens enough to take all the adjustment in the head bearings. Generally i have removed the alloy damper housing and machined off a couple of mm from it, then reassemble and all is fine. The lower FF 36 washer is important too, if left out it will alter the geometry........But generally if the lower guard stay is too close to something it is usually because the stay is too high, the wrong one (too long) and also the difference in exhaust header pipes makes a big difference. I have had to alter several guard/stay set ups to allow the full compression of the suspension and this must be done with the shocker connected but the spring cases left off so you can lift the forks up against the shock absorber bump rubber. The lower the links are able to come down at the front, the greater the chance of the shocker like an AVO hitting the rear inside of the upper link, and this will be dictated by the lower shocker eye bolts in particular. Because the stock front end has long stiff springs, this lifts the front of the bike and gives plenty of travel without bottoming out........but this condition is what causes the bad geometry of the links as opposed to the Brampton forks........The girdraulic forks with less travel and the links in a safer position then replicates that of the Brampton's. It is only the spring cases that limit the travel on full compression when the new stem is installed. I take note of Vic's comments about friction, but the facts are that the load factors from the poor link geometry especially on the lower link are proof that at least the interference fit of these large bushes is overcome by high friction and they readily spin in the housing, thus the large eyes wear quite badly and are difficult to reclaim true and square to one another. there are endless ways to improve these bikes, some things you just have to try and see what happens.........To this date there is nothing negative about what has been done, just a bit of fine tuning here and there to suit each bike/rider combination.
 

bmetcalf

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VOC Member
"The number stamped on the damper ends in a 7 for the originals and an 8 for the stiffer ones. "

I've looked at mine and didn't find a number. Where should I look? {It is on the bike.)
 

greg brillus

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VOC Member
The other thing is that some who have installed the kit are not getting the assembly right.......case in question.......On our North Queensland rally back in September last year, one of the riders bikes had the mod done.......he felt the bike was better but not entirely sure........when I checked the bike, the front end was horribly topped out, with all my weight on the bars I could not push the front end down at all. I can't remember what springs he had used, but he had not trimmed them down at all. After I showed him how nice the front was on my bike he realized the difference and hopefully put it right when he returned home.
 

timetraveller

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The number is stamped just above the lower eye, to the right if the damper is held so that the adjuster screw is to the left. On the picture the number is 1447.
1585040417840.png
 

stu spalding

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VOC Member
When I fitted the J.E. kit I was having problems with the top link hitting the damper and requiring the removal of a lot more material from the link than normal to gain clearance. The problem turned out to be that the AVO damper was an early one that was slightly longer between centres than standard and was rectified by plugging and re-drilling FF57 (the long one). Cheers, Stu.
 

stu spalding

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Quite right Norman, it came direct from AVO's and was fitted to the standard steering before I had considered a J.E. conversion. Cheers, Stu.
 

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