Can stock forks be lowered internally?

[dma251]

I am switching to clip-ons with my 1990 cafe-FJ project, and I want to make these LOONNNNGGG skinny forks a little shorter.

By moving the bars below the triple-tree + I slid them up about 1/2" previously, it's a fair amount sticking up above everything else.

I see in my manual there may or may not be a spacer in the 1990 forks I have.  The manual isn't clear.
  Any ideas?

[Mark Olson]

sure , get different springs that will require spacers.,  remove your horn or it will smash into your fender when you ride .

[the fan]

Yoou can shortenthem internally, but heep in mind that you will sacrifice travel if you do so. I shortened forks for a lot of dual sport riders in the past with all types of fork.

It's a little more involved than simply shortening the spacer/ spring. Simply shortening the spacer will lower the bike but you run the risk of the internal parts getting out of line or binding if the forks over extend. In most cases I made a spacer for the top out spring located on the damping rod or cartridge. This kept the forks from over extending and did not limit the travel any more than shortening the spacer already had.

IIRC I used tubing purchased from Mcmaster carr to make the top out spacers.

The next thing to consider is that you will need to stiffen the fork springs and calculate new sag numbers based on the now modified fork travel. You will want to see appx 25% -28% of the travel as the new race sag number (bike + rider). What this means is that if yo shorten a bike with 140mm stock travel by 30mm you now have only 110mm travel to play with. at 140mm you should have seen around 35-39mm race sag and12-15mm free sag. With the new 110mm travel number you will want 28-30mm of race sag, but maintain the 12-15mm free number. This will necessitate a fairly stiff spring and will compromise ride quality, althouge this can be manipulated with oil weight or a valving solution.

Not sure if that helps, but its how I did it.

[dma251]

That helps a great deal.  Thanks for taking the time.  I disassembled one side, and this is what I found.

It never occurred to me about the top-out spacer, but you are absolutely right.  

Okay.  I need 2" to go away, and I am willing to make sacrifices...    If I shorten the spring 2" (which side of the spring should I cut?), and I make a top-out spacer for the bottom-end, what can I do to increase the stiffness?  

Also, I marked on this photo where I thought the top-out spacer would go, but now I think it should be on the other side. 

[Mark Olson]

aww yuk , math sucks.

if you are not buying new springs like race tech, which need spacers. and will work for your purpose.

go the cheepo route and compress the stock spring by clamping hog rings onto the coils then no other parts necessary.  (hog rings are used in chain link fence)

do so at your own risk. 

[dma251]

aww yuk , math sucks.

if you are not buying new springs like race tech, which need spacers. and will work for your purpose.

go the cheepo route and compress the stock spring by clamping hog rings onto the coils then no other parts necessary.  (hog rings are used in chain link fence)

do so at your own risk. 

I am not going to be buying different springs, unless chopping these doesn't give me what I want.   I think I will cut them down and try to submerge them in a tub of cool water while I heat the cut end and bend it flat.   

I would worry about a hog ring opening up and causing havoc as it works it's way down the fork tube.... 

[Mark Olson]

that's the whole at your own risk part. rings open up and damage may occur.

you will find cutting the spring 2" shorter will not transfer to the front end lowering 2".

there is a progressive weight transfer that takes place and you will drop more than 2".

consider making spacers out of pvc pipe .


An alternative is to get the fork assembly off a 87-88 fzr 1000 , complete with triple tree , wheel ,rotors , brakes , fender , clip ons .

this will give you the drop you are looking for and the bars in the right place as well as 320mm brakes and the 3.5"x 17" front wheel and you can use stock speedo.

you are gonna do it anyway so why not just go all in.

[FJ_Hooligan]

You will make the spring stiffer by cutting off the tighter wound coils. 

In a progressive spring, the tighter coils bind and that's what makes the spring progressively stiffer as the bound coils simply act as a spacer at that point.  You can get there directly by cutting some of the tighter coils off.

[dma251]

It's done.  When it's up and running I'll find out how the ride is.   Maybe it will be so bad it will convince me to get an USD FZR front end....

I installed the 1.5" cutoff from the main spring to the top-out spring.   I used Type F ATF fluid which supposedly is around 20w. 

I was shooting for 1 3/4" shorter, and it looks like I got it.  The tubes are now flush with the top of the triple clamp, and the bike appears to be sitting pretty much the same as it did before...

At the very least it cost me only $4 for fluid.  I reused the fork seals and wipers.  I expect to either be into this again soon, or moving on to USD, so I'm not putting money into upkeep yet. 

Clip-ons should be here early next week!

[chiz]

Consider this.... I wanted a shorter fork for my rocket3 I went a Kawasaki front end and rear end... I was told to cut the damper rods to the length I wanted the reduce fork length (then just re thread the rods for bottom bolt). I'm a little fuzzy, but this will pull the sliders further up the tubes at rest,  travel will be reduced but you will still be able to get original springs in but it will be a stiffer ride.
Chiz