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KJ790

KYB SSS fork problem

20 posts in this topic

I'm the first to admit, suspension is probably my least knowledgeable area on a bike. I can change fork seals and bushing, and turn clickers and what not, but I don't have any experience with valving. I recently bought a racetech gold valve kit for my 06 YZ450F. I followed the directions, everything seemed to go alright. However now I have a problem with the forks. When the wheel comes off the ground (going off of a jump, heading through whoops, or even pulling a wheelie), the forks seem to extend very rapidly until they reach the fully extended point, where they seem to stop violently with a clunk. It is so bad that when I go off of a jump the forks extend and when they hit the end it pulls the front of the bike down (almost pulls the bars out of my hands). It is like there is no rebound damping or something. I'm figuring I must have put something together wrong, but any insight into what I should look at before I pull them apart would be great. Thanks guys.

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Sounds like a bleed problem , davej has a good guide on bleeding the tc fork

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I know this sounds crazy, but I've done it once. Make sure that small aluminum rod is back in the rebound piston...if its not in there. You wont have any type of rebound adjustment

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Thanks guys. I know that the aluminum rods are in there, so that's not the problem. It could be a bleed problem, I followed the directions in the owner's manual, which I have heard aren't the best way to do it. I've never had a problem in the past with this, but it is definitely a good possibility. Any other ideas?

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Overfill the cartidge..."force" the base valve in - must compress IC spring, then bleed by compressing full stroke.

I do it a simpler way...but it's hard to describe.

Are you sure you didn't remove the mid valve rebound shims?

They are on the top of the piston, or nut side.

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I think it is very important to not overfill the reservoir. If you do then the area behind the piston has a vacuum after the purge point. There are of course many opinions about what is happening inside the KYB TC forks, but I’ve found this to solve many problems all in one.

Setting the ht/volume per your manual, then leaving the o-ring just proud of the cap at the time of the final purge allows the pressure to equalize. Then you can seat the cap and not have a significant vacuum in the inner chamber after the cartridge purges. This promotes stability in the system. We added in testing a bleeder to the cap as the 2010 Showa CRF250 did in the production version. The above technique seems to overall work fine and not require and drilling and modification.

BR,

Jer

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Two things that come to mind here, one of which jumped up as soon as you said something about the manual. I know you well enough to think that you more than likely did not get caught in this one, but I'll float it out on the pond anyway. When you came to the part about the gap there was supposed to be between the damper rod lock nut and the rebound adjuster, you did end up tightening the nut against the adjuster, right?

http://www.thumpertalk.com/forum/showthread.php?p=8002008#post8002008

OK, that out of the way, my guess is air in the inner cartridge, too. This, based on what I learned from DaveJ, is how I do it:

http://www.thumpertalk.com/forum/showpost.php?p=8762814&postcount=39

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Two things that come to mind here, one of which jumped up as soon as you said something about the manual. I know you well enough to think that you more than likely did not get caught in this one, but I'll float it out on the pond anyway. When you came to the part about the gap there was supposed to be between the damper rod lock nut and the rebound adjuster, you did end up tightening the nut against the adjuster, right?

http://www.thumpertalk.com/forum/showthread.php?p=8002008#post8002008

OK, that out of the way, my guess is air in the inner cartridge, too. This, based on what I learned from DaveJ, is how I do it:

http://www.thumpertalk.com/forum/showpost.php?p=8762814&postcount=39

Yes, I tightened the lock nut against the adjuster properly, I have seen where that has been confusing for people in the past. I guess I will have to try bleeding them differently and see if it fixes it (unless I see something obviously wrong when I take them apart of course). If it is air in the chamber then it seems odd that it has never happened to me before on any of my bikes when I would change the oil in the forks, and that this time it seems to be with both forks. This is what makes me think I screwed something up with the valving.

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I figured it out, I'm just an idiot. I took them apart last night and found that I didn't have the total thickness of the midvalve right, so basically there was no rebound damping. I rode it today and it feels great. Lesson learned :)

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Having same problem on 09 YZ250.  Previous owner had susp. work done, and nut on cartridge rod fell off for me, wreaking havoc in chamber by destroying shims.  Replaced rebound stack:

10 x 2

12

14

16

13

18

20 x 3

... which was what I found on other fork.  

 

Have had it apart several times; added 3 20's, spring spacer, more oil, but still clunking at top of return as if there is no rebound happening.  Tried another fork from son's bike and problem is definitely here.  I know cause sounds like air, but I've not had problems when I've changed fluid before, and I've had this apart several times with same result.  

 

What problem with total thickness would cause no rebound damping, as described above? 

 

Thanks.

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The midvalve not shutting allowing oil to flow the wrong way

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10-4.  Plan is to disassemble other fork and lay parts side by side to see what's different/missing with attention directed at midvalve. (Should have thought of that sooner)  

Thanks mog.

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I would drill out the ics piston for bleed holes as well.  that would be another step in your favor. 

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I would drill out the ics piston for bleed holes as well.  that would be another step in your favor. 

Ok, thanks.  Going out to disassemble and will post pics for discussioin...

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Bad fork with clunking at full extension:

 

Nut

16 x 1.62   washer

10 x .26

11 x .11

12 x .11

13 x .11

14 x .11

16 x .11

18 x .11

20 x .11   5

 

---------------------------

 

17 x .15   2

11 x .15   2

14 x .11

16 x .11

18 x .15

20 x .15   5

20 x .11

Collar/Spring

Plate

 

"Good" fork from other side:

 

Nut

16 x 1.54   washer

9.92 x 2.4

12 x .11

14 x .11

16 x .11

13 x .11

18 x .11

20 x .11   3 

 

-------------------------

 

17 x .30   2

11 x .30

12 x .15

14 x .11

16 x .11

18 x .11

20 x .11   6

Collar/Spring

8 x .14

Plate

 

There is a bit of damage to "piston internals" could this be a deal breaker? ( BTW I'm a 50+B woods rider for reference)

bad valve.jpg

rebound shim stack 1.jpg

Edited by CG Power

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Well, first number is od in mm and second is thickness, correct?  This was originally assembled by a suspension shop for a young, speedy mxer. I'll search for a yz woods set up once I solve this problem.

 

But as it turns out, put shaft from bad into chamber of good and no clunk.  (Have access to kid's forks for test rides) So apparently I'm barking up the wrong tree, but that's where the damage was.  That leaves compression adjuster or tube as culprits.  

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Narrowed it down to the cartridge cylinder which must have been marred either during original catastrophe or when I removed the nasty bits.  Pricey part to replace for a five cent nut coming off.  

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All along there was a bit of a "spot of resistance" in the tube that I hoped I could ignore and make it go away realizing how much a new assembly is.  Apparently not.  Now I've got time to arrange a YZ woods stack while I wait on arrangements for new cylinder.

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