Fork Springs

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johnavico
Posts: 24
Joined: Mon Aug 04, 2014 12:02 am
Location: Australian living in Italy

Fork Springs

Postby johnavico » Fri Nov 07, 2014 8:36 pm

I'm in the process of rebuilding the 35mm Marzocchi forks of my 250 Desmo. The tvvo springs are of different lengths, vvith a variation of 40mm in the free lengths. Both of them have 54 coils. Should I be vvorried about this?

John

graeme
Posts: 988
Joined: Sun Mar 25, 2012 12:00 am
Location: Tasmania Australia

Re: Fork Springs

Postby graeme » Fri Nov 07, 2014 9:08 pm

I would not use them like that.
Sorry I don't have the spring lengths for your springs, but someone here will.
You could take both to a spring maker and have them reset or new ones made.
(what happened to your W?)

Graeme

johnavico
Posts: 24
Joined: Mon Aug 04, 2014 12:02 am
Location: Australian living in Italy

Re: Fork Springs

Postby johnavico » Sat Nov 08, 2014 9:39 am

Thanks Graeme. My kitten pinched the VV and it's beyond my manual dexterity to get it back in ;) ........ Hopefully someone vvill knovv the correct spring length.

John

amartina75
Posts: 347
Joined: Tue Aug 21, 2012 1:13 am
Location: Cincinnati, OH. USA

Re: Fork Springs

Postby amartina75 » Sat Nov 08, 2014 2:36 pm

John,
I'm not sure exactly which forks you have but if they are the ones I think they are they should look like this.
http://www.ducaticlassics.com/Parts/Model/250,%20350%20and%20450%20Desmo/68-74WD19/
They are basically the same as the Widecase Scramblers.
The fork springs fit inside a spring tube, look at the link for the part I'm referring to.
If yours do not have the tube then your springs have already been replaced, which is likely given they aren't even a matched set. As to the length you need it doesn't matter too much. They need to fit inside the tubes with enough clearance to not scrape or bind and they can't be too long. They need to be close to the right stiffness for the weight of the bike and yourself. Once installed you should have approximately 1/2" of preload, more or less depending on how you want the forks to feel. You could use springs that require no preload spacer or ones that a 4" long spacer, and anything in between. The springs need to fit to the damper rod at the bottom and be matched to your spacer or the tube cap at the top. You could take your fork leg to a local shop and see if they have any springs to fit or order some from a maker of springs. I've had springs custom made before by a U.S. Company "Sonic Springs" I was very happy with them and they were cheaper then Racetech. There is a lot to setting up forks, many variables and they all have an effect on how they work.
Spring rate, oil viscosity, oil amount, preload, sag, travel, ect.
Do a little searching on the web about motorbike suspension.
Good luck,
Aaron
1966 250 Scrambler
1970 450 Jupiter

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: Fork Springs

Postby ducwiz » Sun Nov 09, 2014 1:43 pm

Have you seen, that In the link http://www.ducaticlassics.com/Parts/Model/250,%20350%20and%20450%20Desmo/68-74WD19/ 460mm is given, under part #25 ?

johnavico
Posts: 24
Joined: Mon Aug 04, 2014 12:02 am
Location: Australian living in Italy

Re: Fork Springs

Postby johnavico » Tue Nov 11, 2014 9:47 am

Aaron - Yes, the forks are fundamentally as in your diagram. Hovvever, they are missing the tubes you mention, as vvell as a fevv other small parts. The same parts are missing from each. So I guess that the springs are replacements, as you suggest. You're quite right that I need to read up on forks, these are the first ones I've dismantled.

Hans - The 460mm length spring vvould give a preload of 28mm (does this sound OK Aaron?). The springs vvhich I have are 454mm and 490mm in length, so perhaps I need to have both of them made 460mm.

John

amartina75
Posts: 347
Joined: Tue Aug 21, 2012 1:13 am
Location: Cincinnati, OH. USA

Re: Fork Springs

Postby amartina75 » Tue Nov 11, 2014 3:08 pm

John,
The factory springs are 23.5mm OD because they fit inside the spring tubes which are 26mm OD.
This means you can replace the springs with ones that are at least 26mm od. The length, as I said is not that
important. Most people would say the factory springs are too long and it's better to have a shorter spring with
a preload spacer making up the difference. If you are on a tight budget you can just find some used springs that fit.
35 mm forks are very common and lots of springs should fit. The best thing would be to get new springs. The forks you
have are popular for vintage racing so there should be someone already making springs that fit. Possibly someone on here
who uses them could chime in. If you plan on riding this bike much you are going to want your suspension well sorted or the
bike may be dangerous or unpleasant to ride. Racetech and Sonic Springs are both US companies that could help
you. Unfortunately I don't know a place in Europe like them, but surely there are many. Hopefully someone on here can help you with that. Have a look a Racetech's website either way there is good information on there.
Good luck,
Aaron
1966 250 Scrambler
1970 450 Jupiter


johnavico
Posts: 24
Joined: Mon Aug 04, 2014 12:02 am
Location: Australian living in Italy

Re: Fork Springs

Postby johnavico » Wed Nov 12, 2014 12:16 pm

Thanks Aaron, I think I've taken in most of the theory novv. I'll probably do one of 2 things: 1. There's a dealer near here vvho has a lot of NOS Ducati single spares, he vvould probably have nevv springs - I guess I vvould need to get tubes as vvell; 2. I have feelers out to find a springmaker vvho could re-set the existing ones to the same length. I'll let you knovv vvhat happens. BTVV, there are many nevv replacement fork springs available on Ebay Italia and Ebay UK, but they are for specific model bikes, and dimensions are not given.....

John

johnavico
Posts: 24
Joined: Mon Aug 04, 2014 12:02 am
Location: Australian living in Italy

Re: Fork Springs

Postby johnavico » Sat Nov 15, 2014 8:30 pm

In fact, I've just bought a pair of Marzocchi springs and tubes from 38mm forks on Ebay UK. Length is 460, dia 33 (33.5?), so they sound very similar to original 35mm springs. Thanks for all the help, John


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