Racetech fork springs in BPF forks?? - Kawasaki ZX-10R.net
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post #1 of 8 Old 12-17-2016, 01:29 AM Thread Starter
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Racetech fork springs in BPF forks??

Hope someone can help with this!!! I've looked everywhere but can't find anything. Maybe I'm an idiot??
I have a pair of .90 racetech springs I want to fit in my gen4 BPF forks (Yes, I'm a lightweight!! about 145lbs).
The stock springs are 238mm long and the racetech springs I was sent are 250mm long. So 12mm longer.
How do I instal these longer springs without having too much preload? Can't see how one would shorten the big white spacer that goes in the bottom of the fork.
Has anyone here installed aftermarket springs that might know the answer? I'm not going to go to the hassle of taking my forks apart if I don't have a method sorted.
Any help would be really appreciated.
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post #2 of 8 Old 12-17-2016, 04:47 AM
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You win few mm by turning out all preload, lets say x mm. Then cut topout springs shorter by 10-x mm using angle grinder. Cutting from one end should be enough (where topout spring wire toutches). Set oil level 5mm higher. Raise forks through clamps 6mm. Maybe Motul 2.5W "VeryLight" is good idea too.

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Last edited by Carlos76; 12-17-2016 at 05:03 AM.
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post #3 of 8 Old 12-17-2016, 06:42 AM
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While Carlos is right, the BPF needs some work, going crazy with the modifications might not be the best idea if you're not sure where to go. In regards to your last questions the spacer is at the bottom of the fork tube. You can see the spacer in the picture (black and white plastic piece). The spacer splits apart, where you can cut to the desired length and then put it back together.

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post #4 of 8 Old 12-17-2016, 03:22 PM
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post #5 of 8 Old 12-17-2016, 03:52 PM Thread Starter
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Thanks fellas!
Ellavarta, thanks man. yeah,it looked to me like the spacer possibly came apart. I imagine the two sections screw into each other?
The spacer mod sounds like the best solution for me
Carlos, is it widely held that the topout springs in this fork are too long and benefit from being shortened, or is that just a solution for fitting the longer springs?
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post #6 of 8 Old 12-18-2016, 08:48 PM
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Quote:
Originally Posted by JohnnyB View Post
Thanks fellas!
Ellavarta, thanks man. yeah,it looked to me like the spacer possibly came apart. I imagine the two sections screw into each other?
The spacer mod sounds like the best solution for me
Carlos, is it widely held that the topout springs in this fork are too long and benefit from being shortened, or is that just a solution for fitting the longer springs?
If memory server correct they just slide out. And having long topout springs is not always a bad thing. Ohlins uses long soft topout springs in all of their cartridges. The issue with the BPF is just that they are hard to tune, and the feel you get out of them is never quite like a traditional cartridge. Notice how the BPF is becoming less and less available on bikes?

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post #7 of 8 Old 12-19-2016, 04:28 AM
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Quote:
Originally Posted by JohnnyB View Post
Thanks fellas!
I imagine the two sections screw into each other?
The spacer mod sounds like the best solution for me
Carlos, is it widely held that the topout springs in this fork are too long and benefit from being shortened, or is that just a solution for fitting the longer springs?
Sure spacer cut is much better.

Regarding length of topout springs there are two storys:
a) I suggested to cut 10mm from topout where the spring is "dead" (see picture above). This does not affect topout spring action, just makes room spring and lets forks extend more as side effect. Spacer cut does not extend fork, easier solution.

b) On evallarta's picture there are some Racetech piston kit parts visible. That kit includes replacement topout springs with much less stroke. Long time ago I was at Racetech dealer and they tried to convince me installing this 300usd kit. Was not convinced and passed on it, because it does not change basic design, pison similar too and don't belive that you get much closer to good aftermarket cartridge, went with Ktech RDS instead. One thing they meantioned was that oem topout springs are too long (mid working section in picture) and for racing shorter ones (Racetechs) are needed and oem long topouts cause confusion with sag numbers. I personally think that for street or occasional trackday there is no difference.

Only thing I would investigate is if it's a good idea to remove few stack shims for you light weigth, but I'm not expert on this.

Race Gen4: K-teck DDS, OhlinsGP+link, RCS17+T-Drive, Kit ECU, MivvFull, ported, light crank, race int. cam.
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post #8 of 8 Old 12-19-2016, 11:39 AM
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Originally Posted by Carlos76 View Post
Sure spacer cut is much better.

Regarding length of topout springs there are two storys:
a) I suggested to cut 10mm from topout where the spring is "dead" (see picture above). This does not affect topout spring action, just makes room spring and lets forks extend more as side effect. Spacer cut does not extend fork, easier solution.

b) On evallarta's picture there are some Racetech piston kit parts visible. That kit includes replacement topout springs with much less stroke. Long time ago I was at Racetech dealer and they tried to convince me installing this 300usd kit. Was not convinced and passed on it, because it does not change basic design, pison similar too and don't belive that you get much closer to good aftermarket cartridge, went with Ktech RDS instead. One thing they meantioned was that oem topout springs are too long (mid working section in picture) and for racing shorter ones (Racetechs) are needed and oem long topouts cause confusion with sag numbers. I personally think that for street or occasional trackday there is no difference.

Only thing I would investigate is if it's a good idea to remove few stack shims for you light weigth, but I'm not expert on this.

You are correct that cutting the spacer does not add more stroke length, but what it does do is keep the amount of installed preload the same. Adding more installed preload is going to make the forks feel even more harsh on initial movement.

Also cutting the Top out spring (TO spring) does change the overall length, but it's so marginal it wouldnt matter. To get the true overall length you would have to full extend the fork which compresses the TO spring and gives you the reading. I think what Carlos is seeing is the fork now sits differently in the stroke which gives the appearance of "growing".

Just a couple things to add, and for others to consider. When you cut a spring, whether a topout spring or a main spring, you change the rate of the spring. So if you were to cut the TO spring you would change the rate therefore change the "curve" of the main spring. As Carlos mentioned the Race Tech kit comes with different TO springs along with spacers. They do this to give you more stroke. While cutting the OEM TO spring is an option, you better be sure you know what you're doing and the affects it has on other things.

And last, Carlos and I are on the same page on the Race Tech BPF Gold Valve kit. For the money they aren't the best (and I'm a RT dealer so that should tell ya somethin). You're better off saving money and getting a full aftermarket cartridge kit.
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