Installing new fork springs - TwoWheelForum: Motorcycle and Sportbike forums
 
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post #1 of 11 (permalink) Old 03-29-2005, 06:40 PM Thread Starter
 
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Question Installing new fork springs

OK plan did not work out as I hoped, the price of education.

I installed Racetech replacement fork springs. Everything went back together no spare parts.

Problem is when I went to set static sag the preload adjuster does not seem to have much effect until I get it cranked in all the way and then still a little more than I wanted. I was hoping for something in the middle range.

My thought as of right now is that I cut the spacers to small, the new spring and spacer matched the stack up of the old spring and spacer. I figured that the heavier spring would give me the same sag with the preload adjuster in a middle position, it was cranked in all the way with stock springs.

I believe my line of logic is incorrect due to the stock spring being progressive and the Racetechs are constant rate.

Anybody have any recommendations on a spacer size? I am planning on adding another 20mm.
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post #2 of 11 (permalink) Old 03-29-2005, 07:02 PM
 
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Was there originally a spring tube between the fork cap and spring? It could be upside down so the spring preload bolt is not pushing down the spring. Does the spacer go between the fork cap and spring tube, or between the spring and spring tube?
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post #3 of 11 (permalink) Old 03-29-2005, 07:26 PM Thread Starter
 
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No worries,

There is the fork bolt on top. Next is the preload adjuster that threads through the center of the fork bolt and is attached to the damper rod. The spring seat stopper is next which sits above the spring collar (spacer) with a spring seat (washer) then the spring. I double checked with each step that everything is in the right way.

As I'm re-reading the Racetech directions I believe I cut the spacer to small and the original is exactly 25mm longer than what I cut. Only 15 min. to swap.

Thanks for the double check. Many times it is the simplest piece put in wrong that take forever to figure out.
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post #4 of 11 (permalink) Old 03-29-2005, 10:22 PM
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Hence another reason that I wasn't feeling comfortable tearing my forks apart! But I'm sure we can figure out the problem...




-Chris
aka Gas Man



Was: 2002 Kaw ZX-9R
IS:


is me till the
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post #5 of 11 (permalink) Old 03-29-2005, 11:37 PM
 
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Quote:
Originally Posted by f4ilapper
As I'm re-reading the Racetech directions I believe I cut the spacer to small and the original is exactly 25mm longer than what I cut. Only 15 min. to swap.
Measure twice, cut once. Are you using PVC pipe for the spacer? A tubing cutter will give a nice perpendicular cut. Better than a hacksaw cut.
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post #6 of 11 (permalink) Old 03-29-2005, 11:43 PM
 
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F4I, How much do you weigh (without gear)? What bike? And what rate spring did you buy?

You did the right thing if the new overall length (spring + spacer) is the same as the old. It sounds like you may have purchased too soft of springs. We'll give you the deal once you answer the questions above. That will help us better figure out what is going on.
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post #7 of 11 (permalink) Old 03-30-2005, 07:24 AM Thread Starter
 
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Quote:
Originally Posted by SpeedWerks.com
F4I, How much do you weigh (without gear)? What bike? And what rate spring did you buy?

You did the right thing if the new overall length (spring + spacer) is the same as the old. It sounds like you may have purchased too soft of springs. We'll give you the deal once you answer the questions above. That will help us better figure out what is going on.
I wieght 165# w/o gear. '03 CBR600F4i. And .90 kg 36.7x34.5x315.

I did remove the spacers I cut and put in the stock ones that were 25mm longer. It put the forks a little stiffer than I was hoping, but was well within the adjustment range. The Racetech instruction did say between 15 and 30mm of preload when determining the spacer length. I have about 20mm of static sag after swapping the spacers.
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post #8 of 11 (permalink) Old 03-30-2005, 07:27 AM Thread Starter
 
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Quote:
Originally Posted by No Worries
Measure twice, cut once. Are you using PVC pipe for the spacer? A tubing cutter will give a nice perpendicular cut. Better than a hacksaw cut.
I cut it three times and it is still to short.

I used a saw-zall and ground it to a perpendicular edge then used scotch bite pad to smooth out.
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post #9 of 11 (permalink) Old 03-30-2005, 10:52 AM
 
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If we had done it, we would have chosen a slightly stiffer spring for your weight, just from our experience. .90s are not a bad choice for your weight, and you will probably find a way to make them work for you, but we have found that the guide that Racetech uses is slightly "off." .925s would probably be a better choice for your weight, but you are probably good. (BTW, Racetech doesn't sell .925s, we accomplish that with .90s and .95s).
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post #10 of 11 (permalink) Old 03-30-2005, 06:52 PM
 
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Quote:
Originally Posted by SpeedWerks.com
) ...(BTW, Racetech doesn't sell .925s, we accomplish that with .90s and .95s).
Please explain.
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post #11 of 11 (permalink) Old 03-30-2005, 09:43 PM
 
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Quote:
Originally Posted by No Worries
Please explain.
The forks are bolted together via the triples and wheel, and work as a single unit - each leg is incapable of acting individually. If you put a .90 in one fork, and a .95 in the other, you get an overall rate of .925 in each leg. (What you actually have is a 1.85kg/mm spring rate for the front end, instead of a 1.90kg/mm rate (2 x .95)).

It's what I'm putting in my R6 that I'm picking up for this year - I weigh ~150lbs without gear, and .95 is a bit too stiff for my liking.

Aprilia actually tried this with damping at one point on their GP (and GP replica) bike - one leg only had compression damping, and the other rebound. I don't know if they still do it or not on their GP bikes, the early RS250 street bikes had this setup but went to comventional forks in '98.

- Roach
- SpeedWerks.com

Last edited by SpeedWerks.com; 03-30-2005 at 09:48 PM.
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