Bultaco Front Fork Springs Recommendations Please.

[old trials fanatic]

Can anybody help who has experience of Bultacos ?

I understand that the Pursang fork springs are about 40mm longer than the Sherpa ones? are they the same spring rate?

When i went to Malvern i noticed a couple of vendors selling "progressive rate" springs for Bultacos 35mm forks. Has anybody used them? Are they any good? Are they better than the std springs?

Reason for asking is that i am trying to sort out the front forks on the James project. The Marzocci internals that Alan Whitton put into Norton outers for me feel a bit "oversprung" and after measureing the springs, there are two springs a short one and a longer one in each leg, they in total are about the same length as Bultaco pursang ones. Approx 38mm longer than the ones out of my Sherpa.

So do i

1. Fit std Sherpa springs with long spacers?

2. Fit Progressive springs think they are WES but dont quote me. A Scottish bloke think Classic Pre65 and Twinshock was his company name was selling them amongst others.

3. Fit Pursang springs?

4. Strap two concrete blocks to the fork yokes to compress the forks?

So Bultaco experts etc please advise.

I thank you

Edited March 9, 2007 by Old trials fanatic

[peterb]

Hello there,

I used to ride new 325's in the North East (UK) in the late 70's, and still have a Sherpa now. In all of these bikes I fitted 25mm long nylon spacers on top of the standard fork springs. Turn them down so there is a spigot fitting into the spring and a matching taper for the fork cap.

Bye, PeterB.

[greeves]

Difficult to answer this one. Oil is very important, so you better try and try, but start with your number 2 (Fit Progressive springs.......) and try different spacer lengths and oil. We have a common friend in Derbishire that knows something about those James, maybe he knows.....

[pedronicman]

Some people seem to forget that the springs in their old twinshocks are 30+ years old!

with all that time sitting compressed/riding the springs will probably of sagged.

it is usual in my experience that you replace sherpa springs with pursang springs of a longer length,

wich overall makes the forks better than ones fitted with std sherpa springs.

[mich lin]

This is an interesting topic and one that cannot be answered without more testing and information. I'd have to say that I'm an expert on Bultaco front forks on the Sherpa but you have an interesting problem. Are Bultaco springs really what you need for a hi-bred project like you have?

Here's how springs work, the wire size and how they the winding is spaced decides how stiff or soft they are, really all you can do in this situation is buy the progressive springs and try them! They will either work so, so, horrilbe or be almost spot on, you simply need to be good enough of a tuner to know. Sorry but that's the facts.

Here's how you modify a spring, if you want it stiffer simply shorten it and replace the lost length with an alloy spacer. Which makes the overall prelaod the same because the lost length of the spring is replaced with the spacer. So go ahead and try those trick Bultaco progressive spings, start with preload spacers to ajust them. If they are still to soft, shorten them and build the spacer.

Now if you want the spring softer, I put them on a grinder and grind away part of the outside of the spring to make the wire smaller. How much? That depends on your desired tuning set-up. I'd have to be there to help you, sorry!

Good Luck, be safe and have fun.

Edited March 10, 2007 by Mich Lin

[b40rt]

Has anybody successfully softened springs as detailed above ?

I recently replaced fork springs on my B40 (standard external springs /forks) the only ones available were solo road springs, probably because no-one uses standard forks, only fiddle. These are much better, but a little stiff. The above method seems a little crude ?

[pschrauber]

In short:

The old springs will loose tension with the time, then they will too "shrink" in lenght. There is already a nig difference between pretty well used springs and NOS.

Then clean up the inerta of the fork, there is a lot of debris inside, does effect damping. Then new slide seals to the inner piston works wonder too.

O hope the stanchions are straight by all means, will otherwise worsen action quite abit.

At last are the lower stanchions still circular or already oval inside, the bore wears sadly too, (where most of the debris in the oil comes from.

To the springs itself I have one fork rrbuilded fixing all things named and mounted NOS springs and this unit works very well, better then first expected.

(so a real "overhaul" is in my opinion at least 80% of the work.

An improvement are the Magicals together with adjustable fork nuts, more progressive which is nice to have. Also the ability to adjust the fork is very nice.

Non plus ultra for Betor are air cartridge systems fittet to the fork, (there are two version available). Here you have the complete control about the performance to the fork. The cartridges are made to your requirements and you have still three different springs and of course the air pressure.

I had recently rebuilded a Betor fork with this system, (two cartridge in each leg, (more weight but in case of trouble ... you have a back up). The performance is really good, but its only worth the effort if all other things to the fork a very well sorted.

[smelling123]

Old trials fanatic,

I think as has been said, you might find your old sherpa springs are shorter than new ones..

I use the progressive magical ones and they are great, as pschrauber says they also make screw pre-load adjusters (although i think its a bit of a luxury as your unlikely to need them when you have the pre-load set correctly).

You really want springs that are stiff enough not to bottom out all the time, and soft enough to provide a good ride over rocks etc. For the pre-load, if you can get about 20mm of static sag (the sag under the bikes own weight) and the laden sag (the bike with you on it) takes up about 1/3rd of the total travel, its about right. The Sherpa will be something like about right as your James will be similar weight.

The oil will not matter regarding spring weight - unless you put too much in and use the hydraulic action to 'help' the spring at the end of the stroke - we used to do this when road racing sometimes.

I don't know if the pursang springs are the same as Sherpa sorry...

[b40rt]

THIS IS AN OLD POST which I have resurrected, its the question about buffing down the springs I would appreciate comments on. Thanks

[pschrauber]

Ok I would ask a specialist in suspension tuning, tell him my needs and the specs of my bike and the specs of the springs I have mounted and then they produce a springs to my needs. The price is around 100 Euro a pair.

www.fahrwerkstechnik.org

[cvgmmartin]

I have "buffed down springs for both front forks and rear shocks and yes it works as far as softening the springs. In fact if you were clever and had a good reason to do it, you could grind down different amounts over the length and create a spring that has a non-linear load-extension curve, but try and find someone who can tell you what that curve should be! That is why it is usually best to just go out and buy what others have proven to work. Also grinding down external springs produces a pretty ugly appearance.

[b40rt]

Thanks, problem is no one makes them that I can find.

Did you grind a flat on the outer edge or what ? Appearance is not an issue as gaiters are fitted.

Thanks

Ross

[woody]

If you know what rate you need Ross, I don't think it costs much to have a pair of springs made

[bultacorock]

Im going to try some Magicals progressive fork springs £ 54. sounds like an ok deal.

some were in the life of my bike schrader valve were fitted to the fork caps and some

nice CNC pre loaders to set the springs up. did they use to put a bit of air in the forks to

help fine tune them .....

Is it really....... Mich Lin...... Banned ...... or is it just a Holly

wood stunt

Edited April 23, 2013 by bultacorock

[bultacorock]

I have seen that Bultaco UK have some fork springs at a really good price has any one tried a set

every thing i have got from Bultaco Uk has been magic so im thinking there fork springs will be to

Thanks for any feed back

BR

Edited April 24, 2013 by bultacorock