Lowering forks?

[Ivan]

Hey was wondering has anyone here ever lowered forks I have some chinese Upside down forks off a dirt bike and am going to use them on a new frame I am building,

I need to lower them by 155mm tho so cant really just put them through the clamps has anyone actually lowered forks?

[ac3_snow]

not me but it would appear Yow ling has, found an older bucket thread..
http://www.kiwibiker.co.nz/forums/showthread.php/117934-Fork-mods?highlight=forks

[Ivan]

chers these are USD so wondering if anyone has had any luck with these style of forks might go pull them apart tonight and see whats inside em

[gatch]

chers these are USD so wondering if anyone has had any luck with these style of forks might go pull them apart tonight and see whats inside em

I think you will need to cut springs.. Unless there is a massive amount of spacer in there.

[Ivan]

I have thought of that well changing the springs to something out of a differnt bike I have a few bits and bobs around but I want the forks to be captive i dont want them just sitting on the springs or its going to bounce around and be unsafe the forks will need some way of tensioning them again

[Ivan]

well I pulled one fork leg right apart tonight,

THey are damper rod forks but the chinese have made them like cartridge forks so when I go to take the top cap off i can only get it so far and have to put a spanner inside and undo the lock nut then can remove the top cap, then I can remove this lock nut which hods this shaft in place very much like a set of Honda RS125 forks but this has a coller once removedthis shaft slides completly to bottom of fork and you can remove the damper rod/spacer it sits at the top of the forks very wierd indeed then this has a bush holding it in place you have to tugthis out and it will slide out of fork stanchion then i can remove the fork tube itself

the springs are so huge being origianly 125 motox forks I now have to try find some smaller springs put these in have the shaft cut down and rethreaded to tension up at new height have the stanchions lathed to fit a new groove for the bush and then trimmed down and re assembled should be pretty easy

These are going to be the same size as a Honda RS125 front end

can anyone recommend springs out of a common bike which are relativly stiff not to hard but firm

[Bert]

well I pulled one fork leg right apart tonight,

THey are damper rod forks but the chinese have made them like cartridge forks so when I go to take the top cap off i can only get it so far and have to put a spanner inside and undo the lock nut then can remove the top cap, then I can remove this lock nut which hods this shaft in place very much like a set of Honda RS125 forks but this has a coller once removedthis shaft slides completly to bottom of fork and you can remove the damper rod/spacer it sits at the top of the forks very wierd indeed then this has a bush holding it in place you have to tugthis out and it will slide out of fork stanchion then i can remove the fork tube itself

the springs are so huge being origianly 125 motox forks I now have to try find some smaller springs put these in have the shaft cut down and rethreaded to tension up at new height have the stanchions lathed to fit a new groove for the bush and then trimmed down and re assembled should be pretty easy

These are going to be the same size as a Honda RS125 front end

can anyone recommend springs out of a common bike which are relativly stiff not to hard but firm

Very interesting Ivan.

how about a few photos of it all apart & parts being made?
This might be a solution for others it it all works out...

re springs, you will need to post a few measurements before commenting.

[Ivan]

Yeah thats exacgoing to do is post pictures,

Was abit late last night when I finally got on here,

Talkingto the engineer at work he said if im lowering the forks by 155mm why dont Icut that much out of springs and see what happens only thing can go wrong is they aint gonna work and its not like Im gonna re need these motox springs the current springs are like 1 metre long

[Ivan]

Ok for the guys intrested are some pictures

Ok so the shaft you see goes from the bottom of forks all the way to top

The plan is to lower the forks 140mm really needs to be 155 but if I got 140 I have some extra travel and can play around with it abit more,

So if I lower them 140mm I am going to need to measure the distance that shaft sticks out top of fork stanchion and when I cut the stanchion down have that same ammount of shaft sticking out top of stanchion again. Make sense? then have a new thread cut on it, I will add more thread tho this time as this thread tensions on the spring causing a preload affect so if I add more I can add more preload if need be, are you still following me?

But the problem is I cant just put smaller springs and reassemble again as you can see the stanchions are quite long and hit the top of fork cap almost immediatly giving me no suspension travel,

So I am going to have to have someone re lathe that groove for the Bush and then cut the excess off to allow me full travel,

As you can see in one picture there is that coller with a lock nut which holds everything together this is at the top of the fork and I am guessing by the looks that is the damper rod directly at the top also pictured,

the downfall with this setup with the shaft runnng the whole way throughis I have a set oe emulators here and they are the right size for this damper but the shaft does not allow me to assemble them in the fork.

Now heres a question for anyone if I was to cut 140mm out of those springs thatwould lower the front end 140mm right? probably better off cutting 130 and then tensioning the rest down?????

Or am I better of measuring my current springs minus 130mm and finding a pair of springs this size?

[Ivan]

final 2pictures are the spring and roughly what i want the forks to look like when finished

[Ivan]

re springs, you will need to post a few measurements before commenting.

Ok so a quick measure up shows I have 485mm long springs with 55 coils

I am planning on making them .70 the standered weight for a rs125 honda

[F5 Dave]

Well it goes to show what two years difference makes. I can actually understand Ivan's posts now!

Those springs are pretty tightly wound, just make sure they don't coil bind if you take a bunch off them. Presumably you are aiming for about 90mm travel. Haven't got the time to get my head around the rest of the construction. If you do fit a retaining bung at the top cap it needs a sealing o-ring.

[Ivan]

haha Cheers Dave,

I dont actually need to modify the external fork tube if that is what you are meaning by a retaining bung?

Yeah the springs are very tightly wound, Im going to try find some springs out of a set of 250 front forks like ZXR etc

Yes 90mm is my target but am allowing 110mm of travel so I have some room for adjustment,

I am abit confused with these forks on how to make any significant adjustments as it does not allow me to use emulators in the current configuration,

My idea I thought of today while working was emulators have the bolt running through them and are adjusted by how much tension the nut has onto the shim stack, If I was to measure the ammount of adjustment on the nut i could then remove the bolt and attach these to the shaft so instead of having the bobbon bolt it would be the emulator running through the main shaft with a thread attached and retensioned this way it would mean the emulators would not be removable without stripping the forks apart which could also prove to be a pain,

I will concentrate on getting these forks machined and new springs fitted then worry about that side of it might just be able to adjust it by braxing and re drilling the damper rods

[driftn]

angle grinder bro just chop the sping. good enough for 2/3 of boy racers so must be a win.

[TZ350]

Chambers used a set of scales to measure the pressure on the spring and for every 10kg.... ie at each point 10-20-30...........50-60kg he would measure the amount the spring was compressed, this seemed to work pretty well.

236658

For what its worth, there are quite a few posts on the ESE thread about springs, measuring and cutting them to change the spring rate. Use Thread-Tools/View Images to find the interesting posts.

[Ivan]

Had my stanchions trimmed down and turned down to fit the bush in its new location my uncle did a awsome job!!! pics to come

[husaberg]

Ill watch this thread as i too have a set of Chinese forks I may end up having to use.

Here is another thread with fork travel discussed
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Little help and advice please. I’m putting together a FZR250 (3LN) chassis as a bucket. The front forks have about 150mm travel which is lots more than another bucket I rode in the weekend that handled superbly. Question is, should I restrict the travel to say about 75mm whilst I have the forks in pieces and, apart from fitting emulators, is there any other mods that would be worth doing? I was thinking of fitting say a 75mm spacer over the top-out spring and cutting a similar amount from the main spring preload spacer. I’m running 3LN wheels front and rear, 2.75” and 3.5” with a single large disc off the earlier model with a late model 4 pot calliper and slicks both ends.

Any thoughts on the rear shock would be appreciated as well. Stock currently but with the major weight reduction not right I would think.

[Ivan]

have a look atmy jdr bike build thread pics are in there it did work but the forks are way to heavy and have no control at all

[husaberg]

have a look atmy jdr bike build thread pics are in there it did work but the forks are way to heavy and have no control at all

Mine seem fine for rebound and comp the forks are actually as light if not lighter than mb5 ones.
The yokes are not to bad but the stem is to all intents solid.
But they are no doubt made out of recycled frypans.
I would rather use nsr or CBR but not that easy to find cheap ones.

[Ivan]

If built like myne you will find they are held in place by a bush work out how much you need to shorten them by and have that bush then moved further up the stanchion by that ammount and trim off the excess as to how much over hang you had at standered if you get what I mean easiest way I have found.

I just pulled the RS50 forks apart to have a look inside and these are differnt so I need to have the thread in the top caps cut further down the fork