Triumph/BSA 1971-74 Four Stud Front Forks.


I have found that these forks tend to suit my frames very well,along also the Faber Framed "Otters" The Mike Mills frames that were specified for Mike's complete concept, and doing a lot of the later work on these forks while at BSA Uberslade Development Centre Mike knew how the forks worked.

Other frames fitted with these forks were the Sammy Miller "Otter" frames too.



We have now decided to see if we can improve these fork even more so.

 It seem like the NEW REH forks have now become the normality for "Britshocks", ther is a big drawback though the price!

 At £1300, and with only old style rod damping.

we think even buying a set of "Four-Stud" forks for £300 and a new set of stanchions for £60,we can with an improvement with new linear springs and the valves below. make a better set of forks?? we will see, so watch this page over the coming weeks to find out.




Race Tech Emulators will be on the way.


Early Fourstud Forks.


Found on Triumph and BSA 500-750cc street as well as Scrambler models early to mid 1970s. The Hex shaped portion at the top of the rod must be removed and discarded. It un-screws from the main rod. The piston assembly should then be tightened and Loctited back onto the rod. The FEGV S3301 Emulator Kit used for these forks requires custom made 20-25mm tall 3/4" PVC Adapters.

It is recommended to replace the stock o-ring with Race Tech Piston Rings FPPR Series. At a minimum, install a new o-ring as every one we've seen is worn out.

There is typically a slot rather than compression holes at the base of these damping rods. The slot is maintained but supplemented by quantity (6) holes, 6mm (1/4") drilled 90 degrees from the stock slot.

Note that Fork Spring length is critical on these models! Stock springs cannot be used, Race Tech springs are a must! Check your stock spring length for comparison. RT springs are 425mm long. Room must be allowed for 30-40mm combined height of the Emulator and Adapter.

Custom FRSP 2550 series Fork Springs can be made if needed at the length and rate required.

 More Details...


NOTE!  Race Tech Fork Springs  are Required for all Trimuph/BSA Gold Valve Installations:

FRSP S2643xxx Street Series Fork Springs (required)

FRSP 2550xx w/Modification Dirt Fork Springs

FEGV S3301 Gold Valve Street Emulators

FEGV 3301 Gold Valve Dirt Emulators

FPEV AD3301 P Gold Valve Adapters, pair



 T140 later type.

Alternate style found on Triumph and BSA 500-750cc street as well as Scrambler models mid to late 1970s. The Top Nut and Screw assembly threaded onto the rod must be removed and discarded. It un-screws from the main rod. The piston assembly should then be tightened and Loctited back onto the rod. The FEGV S3301 Emulator Kit used for these forks requires custom 20-25mm tall 3/4" PVC Adapters to replace the top nut. Thus the modification are basically the same as Type 2-5 early models.

It is recommended to replace the stock o-ring with Race Tech Piston Rings FPPR Series. At a minimum install a new o-ring.

There are slots on each side of the rod, 1 upper and one lower rather than compression holes at the base of these damping rods. These slots are maintained but supplemented by quantity 6 holes, 6mm (1/4") drilled 90 degrees from the stock slots.

Note that Fork Spring length is critical on these models! Stock springs cannot be used, Race Tech springs are a must! Check your stock spring length for comparison. Race Tech springs are 425mm long. Clearance must be allowed for 30-40mm combined height of the Emulator and Adapter.

Custom FRSP 2550 series Fork Springs can be made if needed at the length and rate required.

 More Details...


NOTE!  Race Tech Fork Springs  are Required for all Trimuph/BSA Gold Valve Installations:

FRSP S2643xxx Street Series Fork Springs (required)

FRSP 2550xx w/Modification Dirt Fork Springs

FEGV S3301 Gold Valve Street Emulators

FEGV 3301 Gold Valve Dirt Emulators

FPEV AD3301 P Gold Valve Adapters, pair


Charlie ~Oo> Right I will try in layman speak how these little blighter's work.

Compression damping in forks fitted with Damper tubes  work on a principle that if you force oil through a series of holes this will slow-down the rate the fork travels to the bottom of its stroke, or even the slightest movement, this is fine on slow speed bumps. but if you hit a nasty pothole for instance the force is instant instead of the oil acting as a damping agent, the jolt is too quick and the oil cannot move that quickly through the orifice holes of the damper tube, and so for that instance the fork becomes solid, and you feel the impact through the bars into your arms and body.

The returning oil on the upward stroke, in most cases returns through a s washer valve of some-sort the oil removes this from its seat and the oil is allowed to bleed usually through holes in the piston that is part of this valve.

The down side of these damper tube forks are that there is no real adjustment to the system.

You can change the viscosity of the oil used , to soften or harden the ride. and you can if taking things a bit further drill extra holes in the tubes for the so called sweet spot of adjustment. but unless you know where to drill these holes or even which ones to enlarge you are really whistling in the dark.

and you may destroy any damping that there was or at best make the soft ride wallow.

So what does fitting emulators do.

 well it makes the compression stroke more controllable. 

 in-that you can adjust the valve to get the right feel for you. and to the use you are putting your forks too.

 simply the holes that controlled you compression damping are done away with? well not quite but usually six large holes of 5/16" are drilled in the damper tube so that the oil has free flow from one reservoir to the other.

the  "Com"damping is now down to oil being forced through the emulator valve, to which you can adjust to get the fork damping to how you need for the use of the forks.

 unfortunately your rebound damping is down to what grade of oil you use or if you are clever to what adjustment you can make to the original damping valve or washer.

I hope this as helped a bit into your understanding of how these so fitted now work.


Later I will try and take photos when I fit a pair of these valves, to a pair of the four-stud forks.





Stuart testing his newly valved "Four-stud" forks in the wonderful Isle-Of-Man.



The pair of forks in the picture have had the legs reversed in the yokes, to put the brake anchor mountings onto the left leg to be able to fit a Yamaha Ty 175 front brake and wheel!

And they also have 2" longer stanchions fitted.


Most BSA "Otters"are classed has "Britshock" machines,and are not trying to class themselves as Pre 65. So these forks make the ideal choice for this "Classic" machine.



This is the Yamaha TY Wheel fitted. Still looks British to me! remember the British Hub Company? This looks a lot like one of there hubs  from the sixties.


What this brake does  is STOP. that's why I am now using them on all of my builds.



By using one type of brake, This is the Yamaha TY 175-250, that is available (Just) I can swap wheels in an emergency. and will always have a wheel to put into a bike that I know works.



The new stainless brake anchor is strong enough not to bend laterally so you get a straight pull on the brake plate with no distortion. New spacers and bushes keep the lot in-line.


            Information about the development of the

Triumph- BSA Alloy slidered forks.

In the 1970's the fork designs more closely matched what was being done with off-road racer suspensions.

In this style the fork is still telescopic but the seal holder and external springs are discarded.

The sliders are now aluminium with minimal clearances between the slider and the fork tube, the springs internal, and the main dampening functionality is handled by the damper rod.

Although the rod is physically similar in appearance to the earlier cartridge, it works entirely differently.

It is attached from the bottom of the slider with an Allen bolt and is about 12 inches long.

The piston is an annular ring that is held into a recess in the bottom of the fork leg.

The piston has oil flow control holes which can be masked off by a loose washer.

The damper rod fits inside the fork leg and slides inside the annual piston. The top end of the rod is slightly larger so as to act as piston on the inside surface of the fork tube, using a ring or O-ring as a seal.

As the forks collapse and extend the two pistons, one in the bottom of the fork tube and the other sliding inside the fork tube as part of the rod, they move oil through the oil control holes of the piston affixed to the fork tube.

Or the damper rod "pumps" oil through the fork leg piston. The resistance to motion is greater in the extension motion than in the collapse motion because the floating washer can float to block or not to block the oil flow control holes of the fork leg piston.

Holes in the dampening rod body, including one top to bottom, act as addition control holes for controlling the rate of dampening and as oil supply passages for the main fork tube piston cavity.

A short spring is placed coaxially around the top end of rod, caught between the underside of the rod piston and the top side of the fork tube piston when the fork tries to extend fully.

This is anti-topping protection. A conical shape on the bottom of the rod matches with a similar shape on the bottom of the fork tube piston retaining nut to provide bottoming resistance from captured oil.

The fork springs are internal and seat into a machined cavity on the top of the damper rod and onto the underside of the top cap.

The fork tube seals are retained in the slider inside a cavity in the slider's top by e-clips or spring clips.

Small rubber boots usually protect the seals.Other manufactures use variations on the last style. One key one is done by Ceriani.

Instead of a straight walled rod Ceriani uses a hour glass shape which eliminates virtually all dampening in either direction in the mid stoke of the fork leg. This gives a plush ride most of the time with no harshness caused by compression or extension dampening.

Another is the elimination of bushes of any kind where the slider is a slip fit to the fork tube making the bush the entire length of engagement between the slider and the tube.


 Most forks from this period have come along  a parallel road and most have the same type of damping, the real difference is that now some forks are thought to be worth more than others.

Triumph BSA Four-Stud forks were one of the exceptions up until recently, (2015) where now the the price paid for these second hand forks have crept up to the price commanded by the others,say Ceriani for example.

The main benefit of using the Triumph/BSA forks though, is that you can still buy most parts to the fork Newly made and at a very reasonable price compared with the other brands.


And  here is a Seal kit that you can purchase as an example.


Damper rod seal kit 

This damper rod kit consists of a set of two damper rod piston rings manufactured of a Phenolic material (fibre resin). They provide much smoother action compared with the standard O-ring. Suits all alloy fork models. £8.50 + VAT a pair. Part no 97-4003P

These are available from LP Williams, at



Wayne has sent me this picture, comparing a Triumph/ BSA four stud fork damper compared with one from a Fantic fork leg, you can see the holes are bigger in the damper tube, and that there is no washer type floating restricter valve on the Fantic/ Marzocchi assembly.



What we are going to do, is improve this damper assembly,On the Triumph/BSA forks.

We will be replacing the O ring seal with either a Williams type seal or a Quad or X ring type seal that is more sufficient.

We will experiment with different sized holes in the damper tube itself and also the floating washer valve.

We are also considering making the complete damper assembly from milled aluminum. We will also be trying progressive fork springs of different values.

The reason to use these forks has I have said, is that you can get, New fork stanchion tubes from any Wassel dealer at a very good price, and that most of the other parts are available newly made.

And now Wayne is making most of the missing, and updated parts for these forks, there is no reason not to use them.

The cast four stud caps were, and are, a bit of a pain, as they crack across the middle! solution is to fit billet made parts, Wayne is dealing with this has we speak. but there are other billet wheel spindle caps avialable.

 A temporary solution is to make up some 2-3mm steel plates to cover the cast caps, but this will mean you will probably need longer studs.

 I am having some stainless studs made that are two threads longer than the original.


Has I have said, Wayne is also making Alloy fork top cap nuts, with or without venting, that are half the weight of the steel ones fitted originally. The vented ones should help to stop the fork seals blowing when under competition pressure.

 One tip I would add though, is  if you buy a pair of caps from,           

I would keep one of your old steel caps, to firstly, tighten the fork stanchion tubes into the yokes, and then when you need to remove the fork tubes, remove the alloy cap and fit the steel one, leaving it loose a few threads before taping it with a rubber mallet to remove the fork leg from the yoke taper.


 The alloy fork sliders seem to be available secondhand for a good price at the moment, and I think there are still some NOS ones about.

I may consider having some new items cast and machined at a later date.

And I have got a pair of billet yokes on order for Stuart's Manic Cub ride, which means that both top and bottom of the fork stanchion can be clamped to adjust the fork height , for the correct geometry configuration, using T140-160 legs.


 Fork seals are available again from any Wassel dealer, the part number is WW 26040.

and steel fork top nuts, WW29158. Just look on e-Bay if it is easier.


 I will update this page as soon as we have developments .



16/05/ 2012.

 I have just got the vented fork caps from Wayne , and they look to be  first class  British engineering. at its best, then again it would be from this guy.

I have also Incorporated into this update  part of some of the work that has kept me from this site for the past few weeks, and has made a use for redundant cast four-stud fork caps.




The fork caps are now available from     Billet Parts UK.


Mike Wallers "Four Stud Fork" Rebuild.






I have been asked for information on how to fit a Cub front wheel into the "Four-Stud" forks.

So Jon here is a couple of pictures,.

Measurements speak for themselves, there is a alloy spacer missing from the pictures.(Mislayed it) this has a radius big enough to hold in the back plate, there is no nut fitted. (red Arrow).





 Spindle is a slide fit into the bearings.



Spacer cut outs to clear narrow studs.

If you are using the T150 legs the spacers need to be a bit larger in diameter, and you will need to double step the opposite side of the spindle..



If you want more photos, please ask, or any more details.


This Page is about to be up dated shortly with a full build of the forks.




I have just managed to get another pair of these "Four Stud" forks  for the first of the New Foster "Otter" builds.

The one I will be keeping as a demonstrator.

So you know I only fit these forks and a Yamaha TY front hub and wheel to all of my builds now.

I must say You now have to pay at least £300 for a set of these forks in any condition.

And the yokes are getting near on impossible to find, and command a price that is nearing New billet yokes, but we like to fit the proper jobs.

Anyway I will do a photo shoot as promised from sripdown to rebuild on these forks,I must say first impressions they don't look to bad and may have been rebuilt recently.


I now have another pair from the same source, and these were rough, but had all the right bits, Yokes, 1971 sliders the ones with the rib, and eventually when I did get them apart the damper rods where all good.

But I did have to use the long damper holding tool to remove one of the bottom Allen bolts, so that was well worth making the tool.

The stanchions were just lacking most of the chrome, the new replacement tubes are the right money but there are several variations in the chrome on them some seem better than others the hard commercial chrome is a lot better but makes them twice the price.


Anyway the other problem I seem to have is getting the correct springs for trials use so I thought I may try making some my self on the lathe. so that is why I have put the Video on.



Update as we go along. 

And more later.

Take a look at Mike Wallers Fork Video too.




 Brian has been trying to improve the standard T/BSA Four-studs by getting everything working smoothly.

 He has fitted new O-rings to the  alloy damping pistons, but had trouble reassembling the damper assembly into the fork stanchion.(Tube).

 So after checking the depth of the seal groove, found the one that was tight had groove


a lot more shallow than the other.

I checked ten pistons and found one that was slightly tight in the stanchion but the grooves were  all the same. The O ring should barely protrude above the face of the piston, or they will stick. The problem is that some of these pistons may have been copied by a machinist that did not realise the problem.

 but most seem to come fro Harris manufacturing, but it would be a simple job on a lathe and a drill to make.

So do check this when you are rebuilding these forks. Brian went along to his friend with a lathe and had the groove machined  out a tad. until the seal was right.



I have just found this document out that I printed of in 2006. about the Yamaha XS 650 forks. 

I have a pair and have carried out the modifications below.

Just an insight to what you can do very simply to improve forks. and they are not a complete mystery.


Yamaha XS 650 Forks.

There are two ways to go in modifying the front fork assembly: air-assist and conventional.

Both have advantages and drawbacks, but both improve the ride and control.

Late XS650 forks are good in most respects but share some of the same faults found in most current fork assemblies.

There is excessive seal-drag and good looking but inferior-performing dirt scrapers cause unnecessary sticktion.

The XS fork (as with other recent Yamahas) has too much rebound damping that will resulting in wallow and rough riding on bumpy roads.

The 650 also have too much compression damping, which contributes to its jolting behaviour when it encounters a single bump such as an expansion joint in the roadway.

To modify the damping remove the wheel and mudguard brake calliper and springs.

Make a tool from a 17mm headed bolt and two nuts to lock together tape this into a socket that fits and use all your ½’ extension bars to get it long enough to reach the damper rod when the fork is fully compressed. The bolt head should drop into the recess if you twist it to find the fit.

Now with a 8mm Allen wrench to fit the damping rod fixing bolt in the bottom off the fork leg and loosen it, while preventing the damper rod turning with the special tool you have made from the bolt. And socket extensions.

Remove the damper rods from the fork tubes. Note there is a copper washer under the head of each of the damper rod fixing bolts, they may be stuck in to the fork leg, which is fine: just be sure they are in there when you reassemble the forks.

Make sure you have recovered the anti-bottoming pistons that slip over the bottom of the damper rods; they must go back in place when you reassemble the forks.

(If you put a small amount of grease onto them they will stay in place while you insert them into the fork leg).

There are two-quarter inch holes near the bottom end of the damper rods.

Drill two more quarter inch holes through the rods so there are a total of four on each damper rod.

These holes control the compression damping; you have just reduced this by about 40 percent.

Near the top of the damper rods there is a small hole. Use a No 54 drill to slightly enlarge that hole, and drill all the way through to the other side of the damper rod, you will have two holes when you have finished. De-burr the damper holes and thoroughly clean them.

You may wonder why we just don’t use thinner fork oil instead of drilling holes.

We could but this way gets better results, besides 10W oil is a better lubricant than 5W.

At this point you have to decide whether you are going to install air caps?

If not purchase a set of 1976 Yamaha IT 400 fork seals, and install them into the forks.

If you are going for the air fork option, install 1976 Yamaha YZ 250 fork seals.

These seals have less friction than any seals we have used. Yes we know the XS650 has 35mm fork tubes and the recommended seals are designed for 36mm tubes but they work.

The stock springs are of the correct rate and length for the XS and need not be changed.

The stock pre-load cam also offers a useful range of adjustment. Although the front will dive excessively under braking.

To control front-end dive we recommend adding more than the normal quantity of fork oil.

This will introduce an air-damping effect that will increase the total load capacity of the fork, while decreasing dive.

With the fork compressed fully and the spring out of the fork tube, pour Kal Gard 10W fork oil in until it is six inches from the top of the fork tube.

Pump the fork slowly until all the air is out of the damping cavitations, and add oil if necessary, until it is again six inches from the top of the tube.

Install the springs caps and brakes and mudguard and wheel

The XS fork will work best as an air fork,

The initial travel will be softer, braking dive is controlled, and of course the forks are wonderfully controllable. With adjustment. For different riding conditions.


We have converted many forks to oil assist and have had no leakage problems.

Make the same damping modifications as above and use the same amount of the same weight oil. You will need different springs; S&W No SP 1530-19 fork springs should be cut to 18.5 inches and installed with S&W air caps.

If you wish to use some other brand of fork caps be sure the springs are cut so that there is .7inch(Point seven) of spring preload when the caps are fully seated.

We found that 10psi was normal working pressure, for all round use. Twisty roads were more controllable at 14 psi and cushy freeway comfort came at 7.0psi. Like the steering and other modification to the bike it just proves with work how much you can improve a 1973 Yamaha.

 More Later.