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THE VINCENT MOTORCYCLE SUSPENSION SYSTEM( Photo of modified rear strut)
Brampton Forks: The ‘A’ item has a longer stem plus the handlebar clamps clamp to the top of the forks whereas on the ‘B’ Bramptons the handlebar clamp is brazed to the forks and immovable. The damper is a brass butterfly nut which was replaced by a bakelite knob on the later units. Provision is made for the fitment of a tyre inflator on the leading edge of the n/s leg. TTR forks are quite different from the standard.  Humphrey  4/23/07
Front Forks: Whenever I've taken forks apart to renew worn eccentric bushes I've always found that the bushes have been turning in the link and worn the
 bores in the eyes of the link. What I now do is to line bore the link and  fit oversize bushes with a modest amount of interference and arrange the  length so that the bushes don't quite meet in the centre. I then drill and  tap 4 BA down through this gap in about the 2 o'clock position and countersink the hole to take a countersunk screw of a length that just clears the surface of the eccentric. This stops the bushes from turning and every so often you can remove the screw and pump some oil in with a  pressure can and see it come out around the side plates. I also drill the ends of the other three spindles 3/32" diam. and countersink, and then cross drill the shafts 1/16" diam. at a position that's roughly in the middle of the bushes. Again you use a pressure can to pump oil in until it appears at the outside. I believe that most fork wear occurs not from being used but from being used dry and un -lubricated.     Roy Cross  4/20/07
Girdraulic fork bushes: I still use bronze for the eccentric bushes as I feel that the bearing surface is a bit narrow for plastic.  Because there is not a lot of metal around the eccentric eyes of the link one can't use too much inteference when pressing the bushes in.  Whenever I've taken forks apart to renew worn eccentric bushes I've always found that the bushes have been turning in the link and worn the bores in the eyes of the link. What I now do is to line bore the link and fit oversize bushes with a modest amount of interference and arrange the length so that the bushes don't quite meet in the centre. I then drill and tap 4 BA down through this gap in about the 2 o'clock position and countersink the hole to take a countersunk screw of a length that just clears the surface of the eccentric. This stops the bushes from turning and every so often you can remove the screw and pump some oil in with a pressure can and see it come out around the side plates. I also drill the ends of the other three spindles 3/32" diam. and countersink, and then cross drill the shafts 1/16" diam. at a position that's roughly in the middle of the bushes.  Again you use a pressure can to pump oil in until it appears at the outside.  I believe that most fork wear occurs not from being used but from being used dry and un -lubricated.   Roy Cross  2-26-07

Filling an original Vincent shock absorber:        First ,  a tip I forgot .    With the  recessed  type  later  D9/2  plug just below the bottom O ring  that causes problems , just fit a thin shim there below the ring to ensure it remains in its  groove .    When filling  I like to use a transparent plastic bottle { so the air bubbles are visable }   at least  a pint in size , with a  spout tipped  cap .  Fill with your chosen  fork fluid .  With the  damper held by its top eye in a vice  - tipped a bit towards  you ,  and its filler plug  opening  upper most   you  screw in the plastic fill bottle tip  into the opening a  couple of turns  {   the  end of the  tip  cut off  of course }   .  Now  with the fluid  flowing down into the damper body  you  begin to  stroke the damper slowly  over its full travel  squeezing  the bottle as  the damper is extended ,  relaxing it as  as its  shoved inwards .   You will see the fluid going in and the bubbles  rising out and into the bottle .  Continue  until  no more bubbles  are coaxed out  ,  indicating the oil has replaced the air within .  Rotate the body  left and right  to move the last bubbles tqwards the bottle spout  ,    also  you can  slack off the vice jaws and  lift the damper free .  Then to  tip it from side to side  -  the bottle still  in place -  the aim to  coax  any bubbles left inside to travel  towards the  filler plug hole  and  up into the bottle .  Finish with the damper pulled fully  out to max length .  Nows the trick .  Replace in the vice as before .  Rotate a bit to one side  and  quickly  remove the bottle  with its spout , rotating  back uppermost .  Fit the filler plug  in about one turn only  .  Wrap a shop  cloth  around the body  and  then slowly  begin  to force the  damper   closed .  The oil will issue  out around the  plug threads - sopped up by the rag  as the  shaft enters the body  .  You may need to ease out the plug a quarter turn  to allow  the oil to escape .     Now  this is  important  .  DONT  close it up completely  , stop  with a quarter  inch of  shaft still  showing outside the  top cap where its entering through the hole -  seen between the  top eye  fixture  and the  top threaded  body plug .     This  is  the trick  it took me  ages to learn . Not to  expel  ALL the  oil the shaft  could displace .  Stopping  short as  described ,  you now tighten the plug fully .    Wipe  off  all  exterior  oil  .  Stroke it a few times  and leave it fully extended  ,    and hang  it up  from its  TOP  eye   overnite .   The next day  stroke it  firmly in the    normal  vertical  position  , it should feel  quite  solid .  Hang it up again  for a few more hours  if it  has a  soft area  of movement  ,  repeat the last  step .   If the floating disc is retained  for front fork use   it will ALWAYS  have a soft movement   if moved slowly  ,  however if  moved quickly the   force  necessary  to  COMPRESS  it  will be  much  greater   , a sign the  2  rate  damping   function   is working .        If  the action is  not consistant  you did not  get  out all the air  , and may have to repeat  the earlier steps  trying to improve on the initial  attempt .         A good hydralic  sealant is needed on the  top  body  plug  threads to  prevent  oil loss  past  those threads .  This  entire  filling process   is difficult to describe - but logic  will  direct you  .    The object is to  replace all the air inside with  the liquid  ,    certainly  easy  -   or should be  .  Its tricky  tho .  Sid .
RFM Frame Lugs: The majority of post-war RFM end lugs were forged, the dies still exist; I say the majority as I don't know for sure whether the first post-war ones were cast or not, but cast versions seem unlikely given the Series 'A' production run. As such I'm fairly certain that the material would have been a low-ish grade steel.  IMHO, the problems are partially due to the jig used for machining the bore which accepts the lower UFM (horizontal) tube; depending on how the operator set this up, the wall thickness could end up being v. thin on one side and sometimes did, now aggravate this with 50 years of owners with no mechanical sympathy slamming the bicycle back on to its rear stand, or pounding away on the kickstart with the bicycle on its stand and the results speak for themselves. Remember that most of the later joints at this point were pinned before brazing, so when disassembling the joint be aware that the brass may be fluid but you'll have to locate the pin as well - and good luck too!

Note also that there are two types of end lug, the later ones did not have the 'half thickness' relief between the tapped boss for the rear stand and large dia. hole (tapped on earlier models), as shown in MO22; however as far as I'm aware the same part No. 'FT9' was retained to the end.

Malleable Iron is now difficult to get as it requires accurate temperature control and special furnaces, as such foundries have, by and large, stopped making it; it has been virtually completely superseded by Spheroidal Graphite Cast Iron, cheaper and more easily produced.    Frank Griffin  9/11/05

Birmabright Fenders: Proper specification Birmabright BB2.  Produced by Bimetals Ltd., Birmabright Works, Clapgate Lane, Quinton, Birmingham, England. (now defunct) Yhis material could hae also been called: Hinduminium 22, Alcan GB M57S, BA 21, Alcoa 510 or Awco 21.  These being the same thing, but produced by other companies of that era.  We only know it as Birmabright because that's where the factory or mudguard manufacturer purchased it from.  Today we know this material as NS4 or in American terms  5251.  ISO designation:  A1 MG2.  I originally thought the material to be an alclad; I hve now proven myself to have been wrong.  Trevor Southwell 5/28/05

Shock Absorber Seals: Take with you the shaft  D 4/i  and seal holder D 12 and an old ring  and get thee to a Bearing Supply like Dixie Bearings. These Viton O rings usually come in two specs., different in color and made to handle more or less heat. Both work well and cost  under a dollar each.  They are easily matched, simply needing to fit into the original recess and exihibit a nice hug on the shaft. An important point. The upper cutoff  D 9/2  had gone through several changes, the later versions having a top counterbore and radial oil escape holes, the earliest pattern none of these. Where they lack these features, provide a shallow tapered countebore and cut with a hacksaw blade two criss/cross shallow slots across its upper face, these to allow bleed off of oil trapped above this face. Clean any swarf in the slots and polish smooth on an oilstone. Then upon assembly add a thin metal shim atop the D 9/2 to ensure that the bottom  ring does not pooch out of its recess.  It  is often found upon stripping the later dampers having the Works machined deeper counterbore with radial bleed off holes that the ring is lying usless and unsupported in this tapered space, thus losing the effectiveness of that lower O ring. Polish the shaft to extend the life of the new seals. Use a top brand of  Fork fluid, 20 wt ., to which I usually add a dollup of 50 wt. motor oil to thicken a bit and add extra lubricant. Sid Biberman 2/17/03
Handling Problems: I'd pull the rear wheel and check the rear wheel bearings. Vins have a tendency to have the wheel bearings start "walking" in the rear. It happened to me once. My bike would "wallow" in corners. I pulled the wheel, noted that the outer race was loose, shimmed it using some beer can as shim stock, and  then loctited it in. One of the best fixes I ever saw was when Charlie Taylor took an old feeler gauge and wrapped it around the outer race. I couldn't get it out years later. I've seen this happen on numerous Vins.  Somer  7/16/02
Filling Original Dampers:  What I have made is a funnel with a 1/8 BSP adaptor on the end to screw into the damper. This can then be filled and left for a while until all the oil has run into the damper, leave for a day and then do as the instructions tell you, compress until almost home , the oil comes back into the funnel. I forgot to mention the adaptor is fitted with a tap, that can be closed to cut off the flow. So when the damper is nearly compressed shut the tap and remove funnel, fit plug loosely, then compress the last bit and screw the plug up tight. The idea is to keep any air out of the system. Trevor  3/24/02
Removing the Front Spring Boxes: I was shown a method many years ago that is efficient and requires only about four and a half feet of strong cord and,  if you don't want to remove your front wheel,  a 9inch length of 1/2 inch diameter steel.
    First, you raise the front wheel off the ground with either the front stands or a jack.  You then loosen the front wheel spindle and remove the nut, but leave the spindle in place.  Thread the cord behind the spring box and tie the two ends securely together to form a closed loop.  Place the top end of the loop over the top of the spring box behind the bearing bush.  (You can use a piece of rag under the cord to protect your paintwork)  Place the lower end of the loop over one of the protrusions of the tommy bar.  Now using the protruding end of the spindle immediately inside of the tommy bar as a pulley allow the cord to wind round this while slowly turning the spindle with the tommy bar.   As you will now see you are using the spindle and tommy bar as a windlass and you can tighten the cord until it starts to compress the spring.  Now you can remove the top spring box mounting bolt.  If, as you remove the bolt, you gently push and pull the spring box in and out on the bolt you can easily feel if you are taking the spring tension off the bolt to the right amount to allow free removal of it.  Having removed the bolt the windlass can be released and the top half of the spring box can be removed to change the spring or the bottom mount removed and the whole unit removed from the forks.  When one side of the forks has been dealt with, you knock out the wheel spindle with the length of 1/2inch diameter steel,  ( rounding and tapering the leading end of this piece of steel helps the alignment)  so that it takes the place of the spindle.  You then knock out the piece of steel with the spindle from the opposite side of the forks and the spindle can then be used as a windlass to remove the other spring box.  I in fact use a spare wheel spindle to knock ou the one in use and use it as my second windlass, before replacing the spindle in it's original position.  This procedure saves having to move brake cables and reset brakes etc.  Of course if you are removing the wheel you do not need to go through this procedure.
    The whole procedure can be carried out in less time than it has taken to type these instructions.  A couple of weeks ago I replaced both my front springs in under an hour.  I hope this is of use to those members who do not have the facilities to make special tools.     D.J.P.  04/25/01
Derek's method to remove the spring boxes is quite effective.  Last weekend I used a modification and what I consider an improvement to that method:  Instead of using a cord and and using the front spindle as a windliss I used a ratcheting tie down.  For final alignment during re-installation I used a jack under the front of the engine.  Basically this is the recommendation provided in the Thornton instructions.   Both procedures work like a charm.  Doug Wood  04/25/01
Rebuilding Shocks: The authorities will tell you that you can send the dampers back to VOC for "professional rebuilding" and get  them back for only $100. I did it. It's really true . But the last 2 dampers I did myself and it was no big deal. I guess the trickiest part is getting the big eye off  the top of the shaft. There should be a small pin below the eye you can punch out (part 966 in drawing M063). Now clamp the shaft and unscrew the eye (D8). Don't scratch or Mar the Shaft!  Then carefully grip the flats of part D13 in a vise and put a rod through the other eye and unscrew again. Now the whole guts should come out.  I
found that by carefully smoothing the shaft - working up to up to 600 grit paper and polishing it, it then had a chance of sealing against the o-rings. I then replaced both the o-rings (D11) , making sure the barrels were in good shape, reassembled , refilled and tested them. That was all it took. There's a good section in the instruction sheets but many sets are missing sections #10
and #12.  Mike Hebb  04/24/01
Powder Coating Girdraulics: To anneal aluminium, it is heated to a certain temperature, depending on its spec. , and then quenched,( Water,hot water, oil,or air , again depending on spec). This is usually 360 degrees C. and over for twenty minutes.
Heat treatment is used to improve the mechanical properties of the material. This is done by one of two means.
1. Solution treating , which is heating to a certain temperature for a certain time, and a controlled cooling period.
2. Natural ageing. which is what it says, but can be accelerated by heating to 100-200 degrees C. for anything from 3 hours to thirty hours, again depending on spec. this then would be called artificial ageing. Personally , I do not think that the blades would have been heat treated after forging, because the act of forging induces strengths into the material .  The piece of material that was placed in the forging tools, would have been solution heat treated, then as I do not know how many stages
the process took, would have probrably been treated(annealed) after each stamping. After the final stamping it would probably been cooled in boiling water.

Looking at my charts for room temperature ageing, the process could be over in 120 hours. Again depending on spec.
So you can see that 200 is not going to affect the blades. Trevor  03/31/01

Girdraulic Fork Blades were made by Smiths Stampings in Coventry. Bristol Aircraft was a myth, as I had always believed for years.  Trevor  03/30/01
Remember that after you have shimmed your front wheel the fit between the fork blades should be a neat slide fit with no side movement or gap when sitting on the front axle.If there is a gap and you tighten up the axle you will tighten up the movement on your forks and handling will suffer.  Doug Brodie  03/31/01
I had a couple of different sets of springs made for my own twin, but was never happy with the result. Then I came across the front and rear springs, and spring boxes made by Justin Mackay Smith (540) 837-2456 , a Virginia number.  In my estimation Justin's springs and boxes are among the safest and best handling around. His spring boxes fit the springs as well. He makes only limited quantities and does not advertise. I believe his set-up has literaly saved my bacon on more than once occassion.   Carl Hungness  03/09/01

Restoring Girdraulics: Sequence - Strip the links, install the bushes, ream, mask off the spindle bushes and very carefully mask the eccentric bushes with 3M pinstriping tape (wonderful stuff, it is).   I then paint and Very Carefully remove the masking from the eccentric bushes while the final color coat is still wet and flowable;  this helps eliminate the paint ridge on this exposed area.  The spindle bushes are trimmed out by the cupped washers, FF10, so the ridge left by masking is not critical.   I do my own paintwork and use catylized polyurethane or acrylic enamel.   Freidman  2/27/01

Do not use the above sequence if you are Stove Enameling.. the oillite bushings will be destroyed.  Trevor
Here in Indianapolis where I live there are several Indianapolis 500 car teams and many attendant suppliers.  My own personal experience with the Vincent shock absorbers tells me I would NOT utilize them under any circumstances for today's modern traffic..even if they were brand spanking new.

 I brought a rebuilt Vincent shock, rebuilt by a KNOWN mechanic within the industry and a NEW Thornton shock to the Carrera Shock absorber company here in Speedway, Indiana...and the results of the test were:  "Carl, throw away the Vincent shock..it is dangerous. This other shock (the Thornton) is great."

I rode the Thorntons, front and read for 25,000 miles and Dave Molloy  (our Thornton distributor)offered to look them over. They came back with a clean bill of health, no work needed. Yet, I was still not satisfied..I had them tested on the shock dyno again..and they were perfect.

While we all dearly love Philip Irving and his designs, we should remember that in l946 the "airplane" type shock was just coming into vogue. If memory serves correctly, Irving did in fact design the first tubular airplane type shock for a motorcycle and I think it went on a Velocette.Ielieve the VIncent got the next shock he designed..state of the art for its day..but its day was 50 years ago.

The technology and shock development in general in l946 was in its infancy. You might be able to "get by" with some stock shocks for your Sunday afternoon jaunts, but in my estimation, you are really taking your life in your hands by installing a stock unit for everyday riding. Take a look at the passenger car shocks of l946..they were Houdilles for goodness sakes.Tube variety came four years later.

Ron Kemp supplies new shocks by Koni (and there are possibly some Armstrongs out there as well). I feel confident the VOC Spares organization has new shocks as well...but if you are a Rider and you want to hit a bump in the road at 40 plus, I would not only install the new shocks, but also the Springs that have been developed by Justin MacKay Smith (phone 540 837-2456). The Thorntons are advertised monthly in the MPH.  Carl Hungness  02/07/01

Standard Shock Absorber: I've  rebuilt near 3 dozen  with good success so feel qualified to offer these few comments.  One  always finds upon stripping these that the 2 little O rings fitted at the Works have aged very  poorly being hard.  A trip to your local Dixie Bearing or similar bearing supply will get you new Viton based seals quite cheaply and these will not lose their superior characteristics over years of exposure to oils and fuels, etc. Take the seal carrier and the shaft with you to assist in    selecting the correct size.  There are several other improvements one should make while the dismantled shock bits lay loosely  displayed. The upper brass plug/bearing D9/2 has been seen in at least 3 different forms as to its upper inner edge treatment.  The earliest - just a flat topped  hole, and then several variations of  recessed or counterbored hole with radial drillings to release that oil forced up along the shaft.  The first plain version is easily improved by champhering the upper hole followed by  saw cuts in a cross pattern down to the bottom of the champher.  Flatten off any raised edges and polish that surface.
Now the oil that  rises up around the shaft can gather in the widened area and excape out those slots you have cut before over pressurizing the lower O ring.

All of these various types of the D9/2 need a thin flat metal washer/shim positioned above the top of that counterbored or
champhered plug to give a stable floor beneath that lower ring, otherwise the rubber ring is able to pooch down in spots - leaving its designed recess behind - and its outer restrant,  and  its ability to grip and wipe the shaft is lost. The second or upper ring often is able to do likewise into the poorly sized fibre washer above it there beneath the top or outer plug. This needs
improving  in a similar manner.

These shim washers must be a nice running fit around the shaft and centered so as not to score it. Modern  fork fluid of 15 or
20 weight does far better than motor oil - foaming less and maintaining its viscosity more effectively.  It is tricky to expell the air  and this is never held for long with that shaft plunging into its inner volume but care and thought can improve upon this.
Sid   02/07/01

Steering Damper: Very often one finds the Vincent damper plates greasy from over-use of the steering head grease fittings.  This is asking for  trouble ! Remove the assembly and give it a good cleaning and sanding of the friction surfaces to restore bite.  Incorrect assembly can impare its proper function, and it MUST be able to clamp together quite noticably, the later double disc pattern is advisable.  I always mark the knob to indicate when barely biting  -- and  mildly -- and when fully engaged for speeds above  65/75 mph. This to enable a glance to inform one that it is indeed tightened to the working mode.

Jack up the front end to ascertain the effectiveness at selected positions of  one's knob, the mark to be pointing dead ahead.
Racing brake plates up front assist in wobble control because weight forwards of the steering head compounds the pendelum  effect so overpowering the dampers ability to regain control of the flailing mass.  For the same reason I  usually pull-in and lower the headlamps  position by relocating the lower headlight stays to bolts nearby on plate FF-32.  Looks neater and more  compact as well.   Sid  Biberman  01/25/01

Thornton dampers outperform the Vincent and Koni by a long shot. You don't have to install the whole outfit to get the benefit of the damper.  The front one is different from the rear. From experience I can tell you that the Thornton type front springs are a vast improvement over the stock Vincent double springs. Mike Hebb  12/29/00
The question was recently posed asking us if Vincent riders have had any experience with suspension modifications , and specifically if anyone had knowledge of the Thornton system.

    At the onset I need to say it is ever-so-easy to be judgemental, particularly about another man's product. While I like the idea of spirited conversation (particularly regarding my favorite motorcycle) I do find that more times than not, the negative attitude prevails when one introduces a new idea.

    Yes, I have had some experiencve with Vincent suspension modification, both front and rear. I covered my own experiences in an MPH article some months back outlining the springs and spring boxes made by Justin MacKay Smith. In a word, I had previously gone to a Vincent spring supplier (in England) with my bike in tow to show him my fully sprung (seat) and rear suspension arrangement. I had new springs wound to fit my existing spring boxes, and utilized a combninatin of "C" and "D" springs up front.

    The results of my test were not completely acceptable. The bike still bottomed out on tall highway bumps.

    I also orderd the Thornton system and while I was very pleased with the shock absorber Thornton has made for them, I  found it difficult to accept the engineering principles utilized for the spring box arrangement. It is entirely possible for the Thornton system to bind and or cock under a given circumstance.

    The idea behind replacing the rear springs is to give the system longer, smoother (and safer) travel. The springs and attendant boxes made by Justin accomplish the task in the safest possible manner. He has quite simply made longer springs and boxes to match. He also supplied me with a set of springs for the front I am very happy with.

    The Thornton system can be made to work and racer Reg Bolton drew us a fine drawing depicting some (minor) bracketry he installed on his race bike to keep the Thornton system from binding.

    Overall, however I must say I was disappointed in the "release" Thornton asks us to sign while utilizing his product. Never in all my years of purchasing speed, power, or motorcycle equipment have I been subjected to such a release and it definitely did not settle well. Signing away one's rights makes me highly suspicious. I know race car and speed equipment manufactures 'right around the world and I have never seen another such "release"

    Personally, I would not purchase any system for the Vincent until I saw the unit(s) Justin has come up with. I have over 20,000 miles in literally all conditions on his system and have encountered road conditions that I deem un-acceptable to good handling, yet I have felt extremely safe with his system. I too experienced the dreaded Vincent Speed Wobble the second day I owned my bike, just in front of an l8 wheeler, and it took all the desire I had within me to continue to own the machine.

    You are playing with an extremely dangerous area when modifying the stock system and I cannot warn my fellow riders enough. Remember, the stock Vincent system on the "C" allows the rear of the seat to go up and down half the distance of the suspension travel, and in its day, with everything new and tight, the machine was adequate. Remember too, the Vincent was probably only the second motorcycle in the world to have a hydraulic shock absorber, I believe the Velocette to be the first (with a unit also designed by Phil Irving I believe).

    Thus, back in the mid-Forties, the hydraulic tubular shock was a brand new item, prone to early leakage. I had mine rebuilt, and then tested on a shock dyno. It was completely un-aceptable. The Thornton shock was new, safe and worked just fine. However, there are also other shocks (Koni for example) that work very, very well.

    If you are considering a set of panniers, or a passenger and plan to do some serious riding, I'd recommend some studious research before purchasing any system. One tank slapper on a Vincent will make your eyes as big as saucers and you may even wind up wondering why you ever got on a motorcycle in the first place.

    This suspension question is a very serious one, treat it as such.       Carl Hungness   10/14/00


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