FF: Forks Modified Steering Stem

[timetraveller]

This business about differences between bikes has shown itself up with two items during this exercise of getting made and fitting new steering heads. These two differences show them selves up as whether or not one has to remove material from behind and under the top link and the movement of the front wheel with respect to the front of the engine, mudguard clearance etc. When John Emmanuel first allowed me to get copies made of the steering head he had developed he insisted that for safety reasons I put something in the instructions concerning the clearance between the front mudguard and the engine and the possibility of trapping the control cables. When John had fitted his, he had to make a smaller diameter mudguard with new supports and carefully position the cables and apply movement restriction. I inserted the relevant cautions into the instruction sheets but so far I know of only two people who have had problems with mudguard to engine clearance, Everyone else who has given me feedback has not had this problem. I do doubt that this is only a matter of whether or not one has inserted the large washer below the lower bearing in the steering head or not. Greg has warned us that failure to insert that can result in changes in the steering geometry but this washer is only about 20 thou thick. ( Don't have one to measure at the moment.) I have questioned people who have had this problem about whether they are sure that they have standard top links etc and so far I have no idea what causes this difference.
The other difference is whether one needs to remove material from the top link or not. I emphasise in the instructions that one should use long eyebolts and as far as I know everyone had done that. However, the difference between Vibrac's bike where he did not need to remove any material, and my own where I had to remove several millimetres is not a matter of thous. It approaches 5 - 6 mm at that point and that is more than is explicable by differences in the diameter of the front 'tube' of the top link. I have never tried to measure the lengths between top and bottom bearings in the steering head but that distance cannot vary by many millimetres or the stems of the steering heads would be either loose or too tight for the top nut to tighten up. It does not seem practical to get two bike with very different behaviour side by side to measure everything so the best that I can say is that so far everyone has manage to fit the new steering heads and most have not had to modify the mudguard etc. Feedback on this open Forum is the best way to exchange experience and ideas.

 

[vibrac]

yes verrily no two Vincents are the same: "No robots used here!" you can see in the 2020 comet thread picture that the Dave Hills stand works just as it did when it was on the Cooking Comet I was expecting a change and had tapped the feet with 2X 1/4 BSF holes in each foot ready to add some aluminum shoes they are not needed I had anticipated a higher riding position but I put that feeling down to the 4" extra long seat even though I reduced the sqab height.

 

[timetraveller]

OK Gentlemen; the panic is now over. What panic I hear you ask. Well the fact that I was told that the new hydraulic steering damper kits produce problems when it comes to fit them. Remember that this kit was designed on a UFM off the bike and although I fitted a crash bar to ensure there was clearance in that area I did not get it right when it came to clearance between the moving end of the ali bracket, together with the moving end of the damper rod, and the front of the engine. Specifically the front valve spring inspection cap and the nuts which hold down the cylinder head bracket at the left front of the cylinder head. I have had to coble together a system which consists of the prototype 'D' engine and the UFM from the late 'C' ex-Cecil Mills bike. With this combination I can now check the problem and two changes are required, both of which can probably be carried out by those who have already got their damper kits and which will be made to any future kits sent out.
The modifications are 1) reduce the thickness of the spacer which fits between the ali bracket and the moving end of the damper rod. These are supplied 10 mm thick and need to be reduced to 5 to 5.5 mm thick.
2) It is also necessary to grind, file or sand a flat at the rear of the moving end of the ali bracket where the M8 screw holds the damper rod on to the ali bracket. This flat can be at 45 degrees so that only the lower face of the ali bracket is cleared and needs to be about 3 - 4 mm deep at its deepest, Without this the moving end of the ali bracket hits the front exhaust valve spring cap.
These two modifications will be made to all future kits which are sent out.
If you have a 'D' breather cap on the front exhaust valve spring cap then you will have to rotate the damper body around the damper rod so that the adjuster knob is at approximately ten o'clock when viewed from the left hand side of the bike.
To those of you who have already bought kits I apologise, particularly if you have already painted or powder coated the ali bracket. If there is any one else out there who already has a kit then it would be helpful if you could get on with fitting it and let the rest of us know what problems you experience. I cannot guarantee that the 'hybrid C/D engine/gearbox/UFM I have just cobbled together will be the same as other bikes to within thous and it really is thous of clearance in this instance that we are dealing with. I will post a photograph of the modified ali bracket later.

 

[vibrac]

Its not easy sorting a hydraulic damper especially when each bike varies I think you have done a very neat job.
I did not use one of yours because I have already gone through the mill with the Comet racers and only recently perfected a short arc bracket from the cylinder head nuts solution so it was a simple copy of parts for me - except I thought a cheap damper would suffice...

 

[timetraveller]

OK Chaps' here is a photograph of an original and a modified ali bracket.. I have placed them on a piece of 1 cm/1 mm graph paper so you can see the scale. About two millimetres has been taken off the top surface ( that is the one at the bottom on the photograph and the one which is most easily seen when the kit is on the bike) and about 5 mm off the other face. That is not enough to cause problems with either the M8 washer or nut which goes on this surface.

 

[hrdaustria]

hello, fitted the walker-emmanuel steering head and normans hydraulik steering damper. modified the steemfittings for needle roller bearings and close side tolerances. hope to keep the water outside the bearings with regular greasing. needed a new front mudguard and stay to clear the exhaust pipe. the alloy bracket for the damper needed a bit of attention as it hitted the front head bolt and the inspection cap. everything fine now. first test ride yesterday, front end a bit too stiff, the springs seem too strong for my weight and height, will try a softer setup.
the steering damper seems an absolute must with this modification, after a couple of tests i ended up with 16 clicks on the adjuster knob.
all the best
michi

 

[macvette]

Here's my set up, bearings in lower link, chinese damper pivoting on it's centre line and 45 lb springs. Standard Vincent damper with long eye bolts
Bike is a Series D so 19 ins front wheel although the mudguard is standard size from Spares Co. Plenty of clearance from exhaust and mag cowl and motor. Top link standard series D so already relieved to clear damper.
I've ridden about 100 miles since fitting the mods, the front end is noticeably more compliant although it wasn't bad before. Downhill braking, front brake only, is improved as the suspension now compresses and continues to move.
The hydraulic damper makes low speed steering much lighter than with the friction damper so the first few take offs were a bit weavy. Currently running 10 clicks on the damper.
Yesterday, I went through finely adjusting the clearances on the links and stem bearings and checking the tightness of everything disturbed by the mods. Afew more miles to set the steering damper if necessary then I'm done

 

[greg brillus]

You normally need to trim the springs if the front end feels "Topped out" though it will settle somewhat after a few rides. I generally set up the right side spring first so I only need to make further adjustments to the left spring which saves removing the wheel. The feeling of the slow speed unstable feel of the bike can be because of some minor stiffness in the steering, mostly because of a new lower felt seal, plus be careful not to over tighten the head bearings as this will have the same result.

 

[aluminiumbronze]

Has anyone used Norman’s excellent set up on a sidecar with or without a short top link?

 

[davidd]

I believe that Norman has stated that the JE stem that he makes is not designed for side car work. The design that I use is designed for side car or solo use. Jim Young has used it on the side car rig he is currently building and Oldhaven was kind enough to do some trail calculations on his CAD set up. It was pointed out that sometimes the use of a short link with an eccentric in the side car position and my steering stem can cause the trail to go negative. This is not unusual when a short top link is installed, it is just important to know how much trail you want. There are too many tire and wheel combinations being used to know ahead of time.

There are quite a few short links around and almost all of them are different lengths. This means you have to do some trail calculations if you are using an unfamiliar top link. I suspect the side car men wanted less trail than the eccentric allowed in the side car position and went to a shorter top link to get nearer to zero. That would be where the easier steering would be. Although the new stems do not change the rake, they can change the trail.

If I were using one of my stems on a side car rig I would just turn the eccentric to the side car position and run it.

David