Anybody Know What Length Sherpa Fork Springs Should Be?

[old trials fanatic]

So does anybody know the length the springs should be in a pair of Bultaco Sherpa Betor forks? Just want to know if they have sagged at all. Oh yeah the bikes a 1981 340 199B but i think they are all the same forks.

thanks

Edited December 19, 2006 by Old trials fanatic

[bob abell]

I changed my fork springs in my 199A with Sammy Miller Springs a few years ago. The used originals now measure 455mm. I think the Miller springs were only 5 or 10mm longer.

[nigel dabster]

The more you weigh the more preload you need. Back in the time I had two preload spacers (about 40 mm and could only just get the top nut on, usually had someone hold up the forks if poss. You can change the oil to a lighter heavier grade to get quicker/slower response.

[legs]

Sherpa fork springs are 48cm long you can use Pursang motocross springs which are 50cm long

[old trials fanatic]

Thanks for that Legs. Are the Pursang ones a stiffer spring also? Not that i want a stifer spring you see just i am led to believe that a longer spring is a softer spring given that the wire is the same. If you know what i mean

[legs]

Pursang spring is same thickness wire just longer which will make them stiffer same as adding spacers.

[sherpatensing]

OTF, I use Pursang springs (from Dave Renham, not anyone else you know ) in my 199B and the forks behave very well. However, I am 15 stone.

Many years ago, I used to preload my Bultaco fork springs with a valve spring from a British Leyland 'A' series engine!

[ksithumper]

Pursang spring is same thickness wire just longer which will make them stiffer same as adding spacers.

Same wire size, longer spring = a softer spring.

Adding preload doesn't change the spring rate, it only adds a pre-load, so you need a bigger force to move it initially. Thereafter the spring rate is the same. Too much therefore and you get a harsh initial ride followed by soggy suspension, or more or less exactly the opposite of what you want!

If you need a stiffer spring, SHORTEN it (heat and flatten the end coil, then grind it square after) and then add a solid spacer to make up the missing length. Much cheaper than buying new springs.

Just be sure they don't coil bind if you take a lot off.(Measure the gap between coils x no. of coils in the shorter spring, and make sure it is more than the fork travel).

HTH

OTF, I use Pursang springs (from Dave Renham, not anyone else you know ) in my 199B and the forks behave very well. However, I am 15 stone.

Many years ago, I used to preload my Bultaco fork springs with a valve spring from a British Leyland 'A' series engine!

Sherpa, that makes them softer, not harder, however stiff your valve spring!

[old trials fanatic]

Thanks guys for all the help.

ksithumper :agree: i was always led to believe a longer spring, if the same wire guage, would give a softer action.

Actually i will come clean here. I do have a Sherpa 340 but my main concern at the moment is a pair of forks i have had done for the James. They are brand new Marzocci turned down and fitted into Norton sliders. Look it's a Pre65 thing and Yorkshire are a bit funny. You know

Anyway the action of the forks is nowhere as good as the Bultaco and not a patch on the ex Ossa Betors in the B40.

After measuring the springs in the new forks they are 28mm od and 500mm long. there are two springs both of the same guage the shorter one approx 100mm at the top. So what i was hoping was i could get some Sherpa springs, new ones, and fit them to my beloved 199B and put the ones out of the 340 into the new James forks.

Still with me?

Well basically it appears that i will have to get Pursang ones and fit them to the James instead.

Hay ho got there in the end and without the help from all of you it could have been an expensive cock up on my part. So thanks and it looks like Mr Renham will get some more of the January salary cheque

Edited December 19, 2006 by Old trials fanatic