shock rebound problem, Jeremy please help..

[kawi72]

I have a 99 KX 250 and I am having trouble with my shock rebounding. Here is some info on my setup:

200 lbs w/ gear
5.4 eibach spring
rebound: 10 out
l/s comp: 10 out
h/s comp: 1 turn in

recently I noticed that my shock was very stiff, and was not feeling the way it should. It had been a few months since I last greased everything so I took apart the linkage and noticed that the lower shock mount bearings were toast. They were all in there but fell out easily when touched. The remainder of the linkage bearings had a little rust but were not seized. I replaced all of the linkage bearings and the shock bearings but the swingarm bearings were fine. I put it all back together, set my sag to 4" (free sag was 3/4") and went riding. While riding the rear end felt stiff and did not seem to rebound to the top of the stroke. (When I push on it with the motor off it will rebound some, but not to the top of the stroke). When I land off of a jump the shock will stay compressed to a point (~2"), If I pull on the fendor it will rebound again and sorta work until a landing or whoop section then it does not rebound again.....any ideas? Could the shock be blown? I have not seen any oil and does not appear to be leaking?

thanks
Jim

 

[shockdoc]

kawi72.....this is a problem that has shown up on numerous KYB shocks. I have seen it happen on 99-01 KYB's whether they are off of Kaw's, Yams, and just recently a 01 RM 250. You will either have to replace the body or have a aftermarket piston with a narrower piston ring. I have had to fix approx 25-30 of these in the last year or so.


doc

 

[kawi72]

shokdoc, thanks for the info but what is the problem with the body or the piston ring? what has happened? what causes it? has anyone else heard of this problem? I would like to understand the problem before I pay to have someone fix it. Also, approx. how much is a shock body or aftermarket piston?

 

[shockdoc]

Kawi72.....The way I had it explained to me was that a few yrs ago many bodies from the KYB factory in Japan were sent out before the final prosess was done on them (after an earthquake 1 person told me). Once the body starts heating up it swells which makes the ID smaller. Since they run such a wide piston ring it makes it start seizing in the body. Once it cools down for 15-20 minutes it frees up. I've seen it happen on most brands that run KYB but seems that more of them happen on the Kaws. At first I was replacing the bodies which did work but then started useing an aftermarket piston with an 8mm piston ring with the same success. This way is a little cheaper. I actually just heard back from my customer today with the 01 RM250 and he said that was the best the shock has ever worked from day 1. It started this right from the beginning before it was ever taken apart for the 1st time. He has 2 weeks on it now & everythings fine. We can't really advertise or give prices here but if you call or e-mail me or any reputable suspension builder they should be able to help you. Good Luck


doc

 

[kawi72]

thanks again shockdoc, I still have a few more questions.....It seems like something like this would be there from the beginning, like on the '01 RM...My shock was working correctly for a while, then this started....Why would this only start now? I know the shock was heating up before....Could it be that the shock oil is broken down and heating up more now? could replacing the oil or servicing the shock help? When the shock is apart is there any damage that can be spotted or any sign of this problem occurring? How would someone recognize this problem without already knowing about it?

another question...as a shock wears out or loses Nitrogen charge, doesn't it act more like a spring? (opposite of what I am seeing). sorry for all the questions but I want to understand the problem before I throw $$ at it to fix...
thanks,
Kawi72

 

[shaggy829]

kawi 72
if the shock should lose nitro pressure the rebound needle can become stuck in the slowest seting causing the shock to hang down .
I would get a good rebuild or tear down and inspection first, considering the problem you are having i would choose repitable shop to do the work ;)

 

[Jeremy Wilkey]

Doug,
Your idea is intresting.. Pro-Action used to talk about this all the time, and well you know what we think of their ideas, but could they still be influencing you?..

Here's what I find werid.. How does the steel piston have a problem when its in a AL body? Secondly I've yet to see one... IT just does not seem right to me.. I think PA has come up with this as a concocketed solution to a sealhead bearing issue. The problem has nothing to do with body shape but piston / body perpidicularity.. I've seen lots of scored bodies, but no seized shocks..

Wether your piston has a 8mm band or 12 if its oversized in relation your going to have a issue.. So the symptoms don't add up Doc..

I've made some calls to some good freinds at Kawasaki... I'll see what they say and get back to this...

Regards,
Jer

 

[shockdoc]

Jer

I know what your saying as I'm really not a fan of putting aftermarket pistons in. I would rather put bodies on these shocks but have had decent luck using a 8mm piston band piston. When I first started seeing this prob. ('99) it was on a KX 250. After several tear downs installing new piston rings, different oils and such would still start seizing after it started warming up. Leave it sit for 10 minutes and it frees up. Talked to Ross Enzo, Steve Sercy and tryed everything. I ordered a new shaft assy from Kaw & without grinding nut off installed it. Still same thing. Put a new body on & it worked great with (both) shafts. I might add...none of these shocks have shown any wear/scoring inside the body. I had several bodies checked with a digital bore guage by a very competent machinist here in Jax & according to him they were final honed wrong. You could see the shape of the body as it got smaller in the middle. No way it was worn that way he said.

Then I started seeing Pro-Circuit shocks & FC shocks that customers had sent to them for same reasons. They all had 8mm piston ring pistons. I'm no big fan of PA as you might think but thats also what they were doing on shocks seizing up. I'm not using their piston anyway. As a matter of fact I just did another 00 KX250 tonight.

Now I will tell you that I 100% don't know what is causing this but have seen approx 50 - 75 of these in the last cpl years which have been fixed this way. As much as you do I am surprised that you haven't come across this. I would also welcome any other ideas you might have as we can all always learn more. I still can't figure out why some shocks work for awhile before they have this problem and I've also seen a new 01YZ250 do this with less than an hour on it. The dealer ordered new body & fixed it.

Like I said these might not be the answers but I do know what I've done & what has worked & what hasn't. I'm not closed mine & I'm open to suggestions.


doc

 

[Jeremy Wilkey]

Doug,
The FC has always ground the edge of the pistons since the days of McAndrews.. If you think about it the taller the piston the worsee any tip will be.

If the problem really is sezing then well I have no idea.. I've never seen it.. But if the problem is scoring which is the (FC purpose in a short piston (MY best guess) )I would venture then the short piston really helps...

And I do see a lot of that. Espically on shocks that have gone long.. I think the seal head is so poorly fited to the shaft and body that it aids in the tip and makes the scorng issue worse..



Regards,
Jer

 

[kawi72]

well...I pulled off the shock and removed the spring..I can compress the shock (it is very hard to compress, and not smooth at all) but it will not rebound at all...I can pull it apart but it is very difficult..the problem occurs all the time so it does not have anything to do with temperature...

With the spring off should the shock rebound on its own? Should it be smooth going up and down? any ideas?
thx,
Jim

 

[dell30rb]

It should be smooth going up or down at a slow speed, and as you try to make it go up or down faster there should be more resistance. I dont think that it should rebound on its own. (I'm not sure though)

 

[marcusgunby]

Should be smooth and return on its own as long as the rebound adjuster isnt fully in.

 

[kawi72]

the rebound adjuster is not all the way in and it still wont rebound on its own...moving the low speed compression adj. does not seem to have much affect...When the rebound is all the way in you cant even pull the shock apart. With the rebound adjuster in the middle or all the way out you can pull the shock back but it will not rebound on its own at all.

 

[KTM-Lew]

You're outa GAS, man!!!!

Sounds like you have lost the gas pressure, maybe a ruptured bladder? If the shock hasn't been rebuilt recently then it is overdue. You could have it charged and see if it holds the gas. Has it ever been rebuilt?:think

 

[kawi72]

I had the shock re-valved about a year ago, and had the nitrogen checked last week...it was 25 psi lower than it should be, but I had it charged back up to the stock setting...I guess I am going to have someone look at it..any last ideas? I will update when I find out more..