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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FF: Forks Modified Steering Stem
- Thread starter greg brillus
- Start date
I expect I might be too late; but yes I will have steel one please.
I have also e mailed you.
Simon Meikle
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?
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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The front AVO won't fit the rear, because of the different lower mountings. The advice to run-in a front damper on the rear applied only to Konis, as far as I am aware.
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.
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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.
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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.
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.
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.
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.
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............
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