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Stock fork spring stiffening using PVC

  • Thread starter Thread starter ikantbreave
  • Start date Start date
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ikantbreave

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So I was reading through the $50 modification thread and decided I'd like to stiffen up my stock fork springs by cutting the springs and putting in a PVC spacer. I think this is why I keep blowing out fork seals. I can't really afford to get new springs right now so.... My question is which end of the springs to cut and how much is enough without being too much? I'm guessing to cut on the looser coils rather than the tighter coils but I just want to make sure. Thanks.
 
You need to cut the tightly wound end. You can cut as much as you like as long as you don't go "coil bound".

Basically you need to make sure that the spring has enough compression left for the full travel of the fork. You can calculate it or even get a good idea by measuring it (measure one "gap" & multiple by the number of coils).

You can calculate the modified spring rate too but as you're dealing with a progressive spring that is pretty difficult so trial & error might be the only way you can go.

On the 550 I did it had 2 springs rather than a progressive. I took away the 4" closely wound spring & that made it about right.

On the GSXR fork that I modified this way I believe I cut off 3" of closely wound springs, again for a good result. Remember you can always cut more at a later date....

I would suspect you have room to cut off 3-4" without problem but I do not know for sure. Make sure you dress the end of the spring to make as flat as possible & also put a metal washer between the spring & the PVC pipe.

The closely wound end of the spring goes at the top of the fork when you put it back in (less unsprung weight). Most people get that reversed. :)
 
Awesome info, thank you. I got some 1/2 inch schedule 40 PVC and washers so I can do this. I'm going to do 3 inches to begin with and go from there. I am going to make sure I put the springs in correctly to begin with before I even cut them. Would 'saggy" springs cause fork seals to fail faster? More pressure from compressing so much and that sort of thing. I have had the tubes apart twice, ensured that the fork tubes were not nicked up, proper oil level and all that and the new seals I JUST put in about a month ago are leaking. :mad:
 
Just be aware that you are doing a couple of things here.
By cutting the spring, you are actually increasing the spring rate, making it stiffer.
By adding spacers, you are changing the preload. which is a quantifiable amount, well documented and measureable.
As long as you keep these two things in mind, you can use this method successfully. It takes a bit of fudging, and the first time is usually not correct. And it is much easier to remove more spring than attempt to add some back.
 
I'd check your upper tubes for nicks and burrs as well. Pitting on the fork tube creates a cutting edge that will ruin seals very quickly. If you cant find better tubes, you can use super fine (0000) steel wool to take down the edges left behind by pitting/rust and go back with a small fine jewelers file to make sure it's baby butt smooth. But, be aware that the pits left in the forks, even though smooth, will be a path for oil to escape past the seal. Some people have filled these pits with an epoxy or JBWeld, but then you have to make sure you get them completely smooth again...
 
TheCafeKid said:
I'd check your upper tubes for nicks and burrs as well. Pitting on the fork tube creates a cutting edge that will ruin seals very quickly. If you cant find better tubes, you can use super fine (0000) steel wool to take down the edges left behind by pitting/rust and go back with a small fine jewelers file to make sure it's baby butt smooth. But, be aware that the pits left in the forks, even though smooth, will be a path for oil to escape past the seal. Some people have filled these pits with an epoxy or JBWeld, but then you have to make sure you get them completely smooth again...
Click to expand...

I'll go over them again just to make sure they're not my issue. Been finding out that short-cuts are definitely long-cuts. :o
 
OEM seals are usually better but aftermarkets usually work for a decent length of time (10k+ on my skunk which doesn't have perfect tubes either).

Make sure you put them in the right way up & don't damage them putting them in.

If you get the "leakproof" ones you need to put them in by hand only. If you drift them in they will leak!
 
This might sound daft but check you put the seals in the right way up. I have seen loads that leaked very quickly after replacement......'cos they're upside down.
 
What is the best method for cutting the springs?

I tried it on a Car coil years ago, and hard time getting it started.
 
Dremel with a thin cutting disk. Cut at an angle. Nessism posted a good picture on here once. Finish off on a sanding wheel or a grinder. :)
 
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