98 KX forks too hard

Questions and comments about converting to beefier forks..
99sr220
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98 KX forks too hard

Post by 99sr220 »

I've done the conversion and need to tune the forks. After playing around with oil levels, they're still a bit hard and deflect.

I'd rather not change the springs. Any suggestions for making them a bit softer? I'm 176 without riding gear.

I'm sure this topic would have been covered before, but couldn't find much searching. If anyone could post a link, especially something with pics, that would be great.
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98 KX forks too hard

Post by SS109 »

Adjust your clickers full soft and go to a lighter weight oil is all that's left to try. Really, the only way to make it right is to get the right springs for your weight AND have it revalved for off road riding. Trust me, it is worth the expense. It made me faster instantly due to the front end staying planted better and increasing my confidence and my endurance went up since the forks were not pounding my upper body.
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98 KX forks too hard

Post by 99sr220 »

I'm not in the States, so it's difficult to get hold of springs. What about just revalving? They're not too bad now, but they slow me down thru lack of confidence.
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98 KX forks too hard

Post by SS109 »

Please fill out your profile so that the membership can help you. We have members all around the world so there just might be somebody nearby that might know some info that would be helpful!

Anyways, getting them revalved makes a huge difference just on its own.
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98 KX forks too hard

Post by 99sr220 »

I added some info to my profile. Regarding the revalving, any advice would be appreciated. The parts required are small, so shipping isn't too expensive.
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Re: 98 KX forks too hard

Post by kawagumby »

Remove the compression valve stacks and take out half of the largest diameter shims. Reassemble and try it out for starters. The shim stacks are held in place by a nut threaded on an aluminum stud - so you need to be careful to not overtighten - use locktite on clean threads. Some guys carefully file down the staked threads before they remove the nut, but I never have and have never had a problem. Use 5wt and start with 120mm oil height.
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98 KX forks too hard

Post by KDXGarage »

Look online for mxtuner 's fork instruction guide, as it will show some late '90's forks being worked on.

Revalving is the key.
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Re: 98 KX forks too hard

Post by 99sr220 »

Thanks, I'm trying to find the link, if I do I'll post it here.
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98 KX forks too hard

Post by zomby woof »

Before you spend any money on a revalve, do yourself a favour and change the fork oil for something lighter. I was really unhappy with the suspension on my race bike, and took the advice of my riding buddies, who all said I needed a revalve. The bike was kicking and bucking, and no matter how I adjusted it (mostly all the way soft), it was brutal. The suspension shop dicked me around so much that I never got it done, and I'm glad.
A suspension guy in my club recommended changing out the stock oil first, and going from there. Since I have some background with lubrication, and understand viscosity, I looked up the material data sheets on the suspension fluids locally available, and got a few surprises. 5W oil is not necessarily 5W oil. In fact, the SAE numbers cannot be relied on to give you a good indication of how it will work in your suspension.
Read this chart (scroll down to see the big one). The number you are concerned with for your forks is the cSt at 40 degrees C (use 100 degrees C for shocks). Note the huge differences in some oils, and how the SAE W numbers aren't reliable.

http://www.peterverdone.com/archive/lowspeed.htm

I recommend you try something in the range of 10-14 cSt at 40 C, assuming your spring rate is correct

I am at 14 cSt in my fork (mx bike) and will go down to 10 to get more range back. The suspension on my MX bike works as well as any I've ever ridden, and better than most.
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Re: 98 KX forks too hard

Post by kawagumby »

One problem with going with a lighter oil vs a revalve, is that you are limiting the rebound function to less than that which is available using the stock oil weight. In other words, you are limiting your options both ways. Way back in ancient times I used to use viscosity changes on the old damping rod forks... because it was just too hard to figure out where to drill and plug holes. That's not the case with today's suspensions.

If you do your own shim-stack modification, you can make it work however you want. I often just flip the bike upside down, use an impact wrench to pull the stacks (one at a time) and add or remove shims based on how I want the bike respond to the kind of terrain I use the bike for. Keep track of the shim sizes and locations. Stick those puppies back in and ride (ok you need to remove the fuel tank and pinch off the tranny vent line). No need for a shop. It may take a little experimentation at first, but it will be worth the knowledge and experience to get the bike doing what you want it to do.


Depending on what model forks you are using, you can go to a forum for that bike and get shim stack designs for woods use from the locals - you just need to do a search... then you have a more advanced starting point than my suggestion of pulling half the largest diameter shims ( which usually makes a huge difference btw).

Some guys put their shim stack setups on this forum, I did for yz forks, for example.
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Re: 98 KX forks too hard

Post by zomby woof »

kawagumby wrote:One problem with going with a lighter oil vs a revalve, is that you are limiting the rebound function to less than that which is available using the stock oil weight. lug holes. That's not the case with today's suspensions.In other words, you are limiting your options both ways.
The range of viscosity that you would use in damper rod forks is so different you can't really compare the two.
If you are altering the compression, I would hope that you would equally alter the rebound, otherwise your forks will never be balanced. That aside, there is more than enough range available within the settings.
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Re: 98 KX forks too hard

Post by kawagumby »

Don't forget temperature affects damping - cold slows response, heat does the opposite - . What works for you in Ontario may not be appropriate for someone who deals with the warmer temperatures of Thailand. If viscosity changes were as effective as revalving, that would be what everyone would be doing.
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98 KX forks too hard

Post by zomby woof »

I'm not sure how that's relevant.
The fluids (original vs new) will react in a similar fashion based on the same temperature, no matter what it is.
Ambient temperature is more critical in forks than it is in shocks (where it will have little to no relevance), but only for a short time. The range I suggested is well within a useable range regardless of the fact that the temps in Thailand are very similar to what my typical riding season is like.
Nonetheless. I'm not suggesting that in some cases a revalve is not a good idea, but that suspension tuning with viscosity is a real option (that most people aren't even aware of) that should, under almost every circumstance, be explored before a revalve. In other words, people will almost immediately default to a revalve when they think they have a suspension problem, rather than following a sensible troubleshooting approach.

When I told my racing buddies (who have all spent big money on revalves) what I was doing, 100% of them said it wouldn't work, and that it was not possible to tune suspension with fluid changes. If you understand suspension, hydraulics, and lubrication, it's quite obvious that it is.
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Re: 98 KX forks too hard

Post by kawagumby »

LOL, we'll have to agree to disagree on that....If you're up to revalving things yourself, it's really quite a simple and rewarding process. But, if viscosity change works well for you, then that's the way to go...just a different perspective than mine - no-one right, no-one wrong :supz:
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98 KX forks too hard

Post by 99sr220 »

Thanks for all the info, it's really informative. Problem for me is I'm not doing the work myself, even if I was capable I don't have the time.
My mechanic is good by Thai standards, but the parts and information just are available to him, so I try and find out what I can and suggest it to him.

Labor costs aren't a problem, but parts are expensive and difficult to obtain. So it would seem that lighter oil and adjusting shim stacks is the way to go. Has any done a pictorial thread showing how to adjust the shim stack? Also, I've read a lot about disabling the bladders. Would this apply to my forks? If I have pics I can print them off and show the mechanic.

Thanks!
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Re: 98 KX forks too hard

Post by kawagumby »

If you are stuck with using a mechanic, try the lighter oil first as zomby wolf suggests (although the fluid isn't cheap), then if that doesn't work well enough you can try that revalve yourself if you're up to it. Google for youtube revalve videos, I bet they're a few out there. Racetech may have a video out there also (they used to). I don't think '98 forks have bladders - you can double check that tho'.

FWIW, Revalving the forks yourself is cheap and easy (I'm saying this for other readers too) you just need to take the plunge (assuming you have some basic mechanical skills and are willing to do some trial and error). Seriously, it is easier than changing fork seals, as you don't need to disassemble the forks and you can just pull the stacks out as I described in an earlier post in this thread. Be aware that oil height is critical and generally you want less oil than is used for MX work...that's why I suggest 120 mm (to start) from fork top with forks fully compressed.

BTW, "adjusting the shim stacks" IS what is commonly called a revalve (for the compression stacks). The cost is virtually nothing - other than some locktite. That's why I recommend it - as I noted earlier, by just removing half of the largest shims. If you get more advanced and find you want to change the thickness and diameter of shims from what is available on the bike already, you then start to spend money on shims - which still aren't very expensive.

Go on a forum like thumpertalk kawasaki two-strokes and see if someone there has published the valve stack they setup for 98 forks for woods work (maybe that info is here too - do a search). You can get a real good idea of where to start that way.

Good luck either way, have fun!
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Re: 98 KX forks too hard

Post by zomby woof »

kawagumby wrote:LOL, we'll have to agree to disagree on that....If you're up to revalving things yourself, it's really quite a simple and rewarding process. But, if viscosity change works well for you, then that's the way to go...just a different perspective than mine - no-one right, no-one wrong :supz:
It's not an either/or thing, but a sensible method of troubleshooting and repair. A means to an end.
It makes no sense whatsoever to default to the most difficult possible solution first, if you think you have a problem.
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Re: 98 KX forks too hard

Post by kawagumby »

Since you're being obstinate about this subject, may I clue you into the fact that for some of us, revalving the compression stack is actually much easier than changing the oil? So "sensible" is in the eye of the beholder. You talk as if your experience is the only option, however, for those of us who have been riding and wrenching for a while and don't need a mechanic (as you seem to do for a revalve) a revalve is not "the most difficult possible solution". I thought I made that clear in a couple of my former posts. Perhaps you hastily skipped my notes on pulling the compression stacks out without disassembling the forks, in your zeal to make your point. Obviously, for you, changing the oil is the way to go and I accept that. :mrgreen:
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98 KX forks too hard

Post by zomby woof »

Professional mechanic and machinist for 30 years.
I hadn't been on, or worked on a bike in years, and followed the advice of my fellow riders. It turned out that I knew more about it than they did. I just didn't realize it at the time.
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98 KX forks too hard

Post by 99sr220 »

To be honest I'm a little confused about what's involved in a revalve, roughly what is the cost in parts and what should I be looking to buy? Looking on ebay, I see fork valves kits for close to $200.
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