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.

 

 

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 www.triumph-spares.co.uk.

 

 

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, www.billetparts.co.uk           

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.

 

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.

 

19/08/2016.

 

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.