steve125

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Oct 19, 2000
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Thanks Terry! If you noticed 10 minutes before your last post, I edited my previous post. :cool:
 

Jeff Howe

Member
Apr 19, 2000
456
1
Might as well pull them out and round file them and save that little bit of weight is the way I looked at it. They are perfectly fit for the trash can.
 

know_fear

Member
May 19, 2000
88
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Now that everyone is happy, here's a question for you. I removed the conventional forks from my KDX 220 because of the underhang and the imprecise steering (due to fork flex). I put on Kayabas from a 2000 KX125. I believe these used forks are totally stock but I rebuilt them and put in 500cc of 5 weight per leg. They're far superior to the KDX forks especially on an MX track but in the woods they leave a lot of room for improvement.
I'm 180 lbs and not a fast rider but we often find ourselves riding in creekbeds and over some nasty terrain that some would call a Trials course. The springs are .40 Kg/mm by my measurements and eventhough the KDX is heavier than a 125, I feel that things need to be softened considerably. These are the bladder style forks but I'm not sure where to start. I'm new to susp. tuning but willing to try improving things on my own (with help from this forum).
So, first, does 500cc of 5 weight sound right? Can these springs be retained by improving things with valving changes?
When giving advice, it'll probably be best to explain things as if you're talking to a six year old!
 

terry hay

Member
Nov 8, 2003
200
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Know Fear
For the type of riding you are doing the springs should be fine, but as you can gather from the content of this post there are a few issues internally. Firstly as a newcomer to the suspension game I would suggest we keep it simple. Firstly remove the bladder (Go Steve!) and the white sealing band from the cartridge. There is also a finely machined washer on the flange at the top of the cartridge where the spring seats. This inhibits oil flow to the lower portion of the fork. With the sealing band removed there is possibly no reason to touch this, but I remove it to ensure maximum flow and replace it with a normal spring preload washer that doesn't seal the area. I wouldn't recommend sitting the spring directly on the flange itself. If you don't have a preload washer you can drill a few holes in the machined one. Just make sure you leave no burrs. Run the oil level at 120mm from the top with the springs out and the fork completely compressed. The midvalve on that particular model has one of the worst production designs I have come across. In fact the 2000 KX fork should have seen Mr KAYABA and his team of designers firmly attached to the testicle clamp. You really need to address the midvalve and base valve to get the best out of this model for your application. Now that we have addressed the design issues I'm going to stop short of any valving recommendations as this conflicts with a lot of the guys on this forum. After all thats how they make their living.
Regards
Terry Hay
 

know_fear

Member
May 19, 2000
88
0
Okay I'll give that a shot. I doubt that I'll be able to get that done and give it a test ride this weekend but I'll let you know. We're starting to get a lot of snow here so the lower trails are still open but getting really muddy.
How about oil weight, should I stay with 5?
 

Jeff Howe

Member
Apr 19, 2000
456
1
I've not ridden a 00 KX 125, but a friend still has a 01 KX 125 with stock suspension and those forks are hands down the worst stock forks I have ever ridden on a MX track. They are so harsh it blows my mind, and that shock is equally as bad. So Terry, Mr KYB should not have been released from the testicle clamp for another full year there.
 

Jeremy Wilkey

Owner, MX-Tech
Jan 28, 2000
1,453
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Well for one I actually agree with all of you on the bladder fork! I must admit I was a die hard who was shown the error of my ways.. But it took some hard lessons first.. Jeff was a principal in that change, our debates are always productive, and spirited.. (I hope you butt chewing comment was in good humor Jeff, I be bummed if you ever thought that your opinion was not welcomed hear by me. I consider you a good friend and I hope you know that!)

As for the bumpers..


I think maybe you guys are missing something on these new forks.. These are not bladder forks as much as they are "Semi sealed forks".. That check valve is there to prevent any low pressures.. I don't interoperate these forks to function the same.. KYB is actually building a pressure in the forks cartridge that will slowly leak out, this enables the fluid pressure to rise without fork travel and solve many of the open Cartridge inconsistency issues. So its not a restrictive barrier issue.. Set the oil level lower and you won't have any harshness but you will get more solid and consistently working fork..

BR,
Jer
 

Onore GT

Member
Feb 20, 2001
27
0
Originally posted by terry hay
Steve
As I mentioned in the post that I thought at first glance Kayaba was attempting to produce a cheap dual chamber. My initial conclusion based on this assumption was that the system was bound to fail due to the fact that the damper rod was not sealed against the top of the cartridge. Oil was bound to escape more easily from the lower portion then it could get back in and we would end up with an emulsified mixture within the cartridge. After I was informed about the "speed sensitive" air spring I had to re-evaluate but still came to the same conclusions regarding flow. In order for the speed sensitive air spring to work effectively I believe we would need to allow a bit more oil to bypass the seal around the cartridge. This could perhaps be achieved and made adjustable by a replacable bleed jet similar to that of a two stroke carb main jet, positioned in the spring seat at the top of the cartridge. Any thoughts?
[/QUOTE

The 2004 KX fork does have a bladder but the purpose of the bladder is significantly different than the old model bladder fork. With the check valve or restrictive barrier now freely allowing oil into the lower portion of the fork and holding pressure in the lower portion of the fork, the fork is less prone to cavitation. Although pressure within the cartridge is still changing as the fork goes through it's stroke, the cartridge is effectively sealed from the drastic change in pressure of the airspring as the fork moves through it's travel.

Thus, with the lower portion of the fork effectively sealed and "charged," the role the bladder is to take up the volume of oil displaced by the piston rod rather than only being used to manipulate the size of the air chamber. There is still some effect of a speed sensitive airspring in the new fork but to much less of a degree than the old bladder fork because the lower portion of the fork is already charged and the bladder is under pressure.

If you think of the fork in these terms, effectively this is a sealed cartridge fork. The top of the cartridge is not absolutely sealed but that is not necessarily a bad thing bercause air can escape from the cartridge and the cartridge is continuously charged every time the fork moves through it's travel to maintain pressure within the cartridge. The oil volume is also much greater than a true closed cartridge fork also. This system is not necessarily better than a sealed cartridge fork, I just don't think we are ready to throw the baby out with the bathwater yet...
 

terry hay

Member
Nov 8, 2003
200
0
Onore GT
The designer of the bladder fork obviously had his own agenda when he first ventured into this design folly. Wether he wanted a poorly designed speed sensitive air spring or a poorly designed dual chamber fork is not important. The fact that the design reeks of failure, is. When such dramatic improvements can be so easily effected by removing the offending items and reverting back to normallity it lays waste to any good intention the designer might have had. Once again I am disappointed that a concept is released in an underdeveloped state, and we, the motorcycle buying public are asked to be patient while they get it right.
Terry
 

steve125

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Oct 19, 2000
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Originally posted by terry hay
Onore GT 
Once again I am disappointed that a concept is released in an underdeveloped state, and we, the motorcycle buying public are asked to be patient while they get it right.
Terry

Yep! like waiting for over 10 years and the CR125 motor is still slow. So Honda threw in some bladder forks just for fun. :confused:  
 

Onore GT

Member
Feb 20, 2001
27
0
Originally posted by terry hay
Onore GT
The designer of the bladder fork obviously had his own agenda when he first ventured into this design folly. Wether he wanted a poorly designed speed sensitive air spring or a poorly designed dual chamber fork is not important. The fact that the design reeks of failure, is.
Terry

Don't you think you are overstating your case a little Terry? I think they could have efffed it up a lot easier than designing an entirely new system. When was the last time you set out to design and execute something poorly?

No but really, I see your point and agree. The fact is that most of this stuff that shows up in production is handed down from factory bikes. Why doesn't it fly for production? The factory forks were made with higher quality components and manufacturing processes? The forks have to be tuned too specifically for each track or terrain? What factory rider desires something that is completely out of the realm of what a normal person desires? It is all these things and many more. Because it did not work well in it's first production version is that reason to completely scrap the idea and start on something else? Personally I am not ready to toss out the latest version. The 04 fork has some pretty cool features and for the most part people seem pretty happy with the fork here. Obviously I cant speak for your side of the world and your customers may have a completely different opinion, however.
 

terry hay

Member
Nov 8, 2003
200
0
Onore GT
Perhaps your right and I am overstating a little. The fact remains that the system is a step backwards from previous models. I'm sure there are many customers out there who are happy with their bikes, complete with bladders. (This doesn't mean they wouldn't be happier without them.)
But, when presented with the task of improving the fork for those who are not, the solution is obvious. This in turn begs the question,"What were they thinking when they produced this?" I would doubt very much that we would find a bladder in a well tuned factory fork.
Terry
 

Onore GT

Member
Feb 20, 2001
27
0
Terry, Point taken, and I guess that is the question of the ages isn't it, "What were they thinking?" Unfortunately there are a lot of steps that happen between design and final execution and lots of places to make mistakes in between. Sometimes problems with the end product are a result of separation of the engineer from the end product, sometimes it is incomplete testing, sometimes it is poor feedback from the testing staff, sometimes it is a misinterpretation by test riders about what the general public will want, and sometimes it is a mistake in production. And then there are all the other considerations about the chassis and engine setup during testing, was the system selected to improve handling with a sacrifice in suspension feeling? As we all know the final production or race setup is a combination of sacrifices to create an acceptable overall package for the rider.

Just curious, have you guys worked much with the new KX fork? Overall what are people's opinion of the new KX fork? Of course you hear people griping about the suspension everywhere but so far in the states I think once people get some time on the bike and get it set up with proper springs when necessary I think people are pretty happy.

Originally posted by terry hay

I would doubt very much that we would find a bladder in a well tuned factory fork.
Terry

Of course production bikes are always a couple to a few years behind what they are using on the factory bikes but you might be surprised by who and when the bladder forks have been used… :)
 

marcusgunby

LIFETIME SPONSOR
Jan 9, 2000
6,450
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My comment would be, i think the Kayaba guys were a bit stuck on how to goto the next level, the TC is IMO the way forward , but patents stop them copying that design, the basic KYB fork was not much different from 95 onwards(when we got the midvalve) since then weve had bumpers and cones(nothing radical IMO)and CVs(IMO mainly designed for the big catridge YZ fork) and now since 2000? the bladder, im still grappling with how it actually improves the fork action in the designers eyes. I know when riding they are not good forks, and they feel good when modded(ie made more conventional)
SO i guess the answer isnt performance, but having a reason to employ R&D staff?

So whats going to be the next big thing?? how are they going to make the next leap?
 

terry hay

Member
Nov 8, 2003
200
0
Onore GT
How dare you employ the voice of reason just when I was getting passionate!
Now I have to climb down from that soap box and start again.
The KXs have been on a downward spiral (saleswise) in this country until the arrival of the KXF250. Since its arrival I have worked on 6 KXFs and I have an RMZ booked in on Monday. I believe they are the same but I'll let you know if there is any difference. Every one is complaining of similar things with the forks. Harsh, deflecting, armpump. Mind you I have to be fair and say that the only time I hear from people is when they're unhappy with their bikes. We had Team Kawasaki out here on Monday testing on our supercross track and overrunning our workshop. Interestingly they also disable the bladder arrangement. We recently set up a bike for Dirt Action magazine in which we left the bladders intact. It was raining that day and we couldn't test sufficiently. We are due to do some more development with them on Saturday. You seem rather passionate about the bladder arrangement yourself. If you have any suggestions now would be the perfect time to speak up as I am always willing to test and the mags are always keen on a new angle.
Regards
Terry
 

Steve47

Member
Nov 23, 2001
103
0
Alright guys,

I know nothing about forks and don't understand how they work! That's why I have my friend Shockdoc helping me out tuning them. The thing I know is how they feel!!

The other thing I know is that I owned every KX250 since 2000 and my 2004 has the worst forks of all. Terry described it perfectly "Harsh, deflecting, armpump" Braking bumps is a nightmare for me right now and my arms are done after 5 hard laps. Not cool!

Yesterday, after reading this thread, Shockdoc disabled the bladder to see the improvement. Now I dnd't get much track time cause it at the end of the night and something went wrong with my shock rebound but I can tell you that the forks are tons better now. I can't wait to go back out and pound some laps.
 

Onore GT

Member
Feb 20, 2001
27
0
Here is your chance to knock me off my soapbox Terry... :) I started using the subtanks back in 01 and have been using them ever since. On the 01 and 02 KXs I removed the internal bladders and just ran the subtanks. The 04 I am again running the subtanks but have left the internal bladders functional. I ride all of the local tracks here in southern California where the manufacturers are doing their production testing so usually I don't have to change much other than the addition of the subtanks, springs, and some additional low speed compression to make the suspension work for me. And with the addition of the subtanks it seems there is a lot less tuning necessary, especially the subtanks with the adjustable restriction. Once you find a setting you can go from track to track with few changes. I can't begin to describe how well the subtanks work, never will I own a bike without them. I know that it is not possible to deliver a magazine bike with the subtanks on it, but after installing the subtanks I don't have to do much more to make the forks work really well for myself.

Jumping off my soapbox for a moment, the other thing that I fail to take into consideration often is that I am fairly tall and strong, and have a lot of leverage to work with that some people don't. I can see where lighter riders would think the forks are horrible as delivered.

Steve, I am curious to see how your test goes, let us know the results…
 

NO HAND

~SPONSOR~
Jun 21, 2000
1,198
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Originally posted by Onore GT
...I can't begin to describe how well the subtanks work, never will I own a bike without them...
What brand of subtank are you using? Is it true that oil will accumulate into the tanks?
 

Jeremy Wilkey

Owner, MX-Tech
Jan 28, 2000
1,453
0
Ongore GT,
I really appreciate your position.. Thanks for taking this down the trail..

As for the subtanks, I would not ride without them either..

As for the oil accumulation this is a small price to pay for condensation...That occurs as the oil vapor condenences after passing across the restrictive barrier..

Terry, here is an idea to try, leave the bladder in and set your oil level conservativly low and you'll have a fork that is more consistent and solid.. With in theory a slightly stiffer overall spring rate..

BR,
Jer
 

terry hay

Member
Nov 8, 2003
200
0
Onore GT
How can you defend a design parameter and then exceed those parameters by adding subtanks? Which, given that the bladder was originally designed to replicate the effect of the subtanks, aren't you simply admitting its failure by adding them in the first place?

Jeremy
I prefer to run slightly fimer valving and lower oil levels as a rule. It gives a more consistant action and often brings the comment "The harder I hit things the better it feels!" Exactly what we're after when trying to entice racers to go a bit quicker
 

darnjr

Member
Jul 5, 2001
199
0
Suspension experts,
What suggestions would you make for the 2002 model forks with bladders? I race cross country as an intermediate and if it weren't for conditioning, my forks would beat me to death. I had the forks and shock revalved after riding a friends 2000 KX that seemed to float over rocks and chop. I had a local shop do a "two-stage" valving job but I have never really been very happy. The low speed is fine, the shock is fine, but the forks are still harsh in the high speed choppy stuff. If I remove the bladders and seals, would the previous suggestions of lowered oil level still hold true? And would further valving adjustments be recommended beyond what has already been done?
Thanks for all the great info,
DA
 


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