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Pulled a suspension apart the other day from an 07 YZ450F that had been completely reworked and set up for a pro rider. The suspension had about 7 hours on it. The re-valve was done by a big name suspension house.

The left rod would not extend from the lug and would suck back in when I pulled it out. The required three-handed operation was used to get the fork apart.

When I got the cartridges out, the rod was sitting about half way up. Pulled the upper assembly out and of course the free piston was cracked.

However, the free piston was still intact. The cracks ran vertically from the top to the bottom, with about three to four cracks running in parallel. In addition to this, the pistons were stained yellow from about half way down to the bottom.

The cracked free piston was obviously leaking, but no fragments of the unit had come off. It was also filled with fluid and the upper o-ring and bushing had a good chunk taken out of it, (the sign of a high quality re-valve).

Needless to say, it had to be replaced.

On the other fork, the free piston was not cracked but was heavily stained as well and I would assume, was nearing the state of its twin so this too was replaced. The feel of the plastic did not feel soft and pliable like a new piston does, but felt very brittle and sharp. Not exactly a scientific analysis, but I think you can understand how different things can feel even with the common touch.

With that, I'm noting declaring that the free pistons are breaking or cracking for one reason or another, but clearly in this case, the free pistons were experiencing some form of material degradation due to, what I assume, a contamination or a reaction, brought on by the fluid or perhaps residual solvents.

The other interesting thing about this build is that they used a special low-friction seal (gray in color) that was severely binding the lower tubes. And I think what was causing this, as I've seen this before, was that their fluid, (again…making some assumptions here) was ironically, reacting with the seal much like some solvents cause rubber o-rings and the like to enlarge. So I now wonder if there is some connection to the plastics and rubbers in some of these parts to certain fluids and/or solvents. Perhaps that’s a no-brainer.

Now...that aside, here’s another update.

When researching the KYB specifications the other day I noticed that KYB was listing a new part number for the free piston in the 09 YZs, and that the part number on the 09 CRFs was unique as well, although all of these pistons shared the same dimensions. So I ordered them up and sure enough, to the naked eye (and a set of calipers and bore mics) all of them are the same size.

So I contacted KYB about this and they replied saying that the material has been changed. No other details provided.

Can’t deny or confirm this, but to be safe, I think I’ll most likely be replacing any broken free pistons in the future with the 09 models.

That is all I have at the moment.

:)

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Maybe some of these super quick suspension guys are not waiting for solvents to dry completely before reassembly? Personally I've never seen any need to use solvents on the free piston anyway except perhaps after drilling and a quick spray with kero and a blow off with the air gun. I wouldn't like to use anything more solvent than that on a plastic part although I do not condone use of kero as a final cleaner of most other parts because it is slightly abrasive.

PMK noted that certain Silkolene oils seemed to react with WP seals some years back.

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Pulled a suspension apart the other day from an 07 YZ450F that had been completely reworked and set up for a pro rider. The suspension had about 7 hours on it. The re-valve was done by a big name suspension house.

The left rod would not extend from the lug and would suck back in when I pulled it out. The required three-handed operation was used to get the fork apart.

When I got the cartridges out, the rod was sitting about half way up. Pulled the upper assembly out and of course the free piston was cracked.

However, the free piston was still intact. The cracks ran vertically from the top to the bottom, with about three to four cracks running in parallel. In addition to this, the pistons were stained yellow from about half way down to the bottom.

The cracked free piston was obviously leaking, but no fragments of the unit had come off. It was also filled with fluid and the upper o-ring and bushing had a good chunk taken out of it, (the sign of a high quality re-valve).

Needless to say, it had to be replaced.

On the other fork, the free piston was not cracked but was heavily stained as well and I would assume, was nearing the state of its twin so this too was replaced. The feel of the plastic did not feel soft and pliable like a new piston does, but felt very brittle and sharp. Not exactly a scientific analysis, but I think you can understand how different things can feel even with the common touch.

With that, I'm noting declaring that the free pistons are breaking or cracking for one reason or another, but clearly in this case, the free pistons were experiencing some form of material degradation due to, what I assume, a contamination or a reaction, brought on by the fluid or perhaps residual solvents.

The other interesting thing about this build is that they used a special low-friction seal (gray in color) that was severely binding the lower tubes. And I think what was causing this, as I've seen this before, was that their fluid, (again…making some assumptions here) was ironically, reacting with the seal much like some solvents cause rubber o-rings and the like to enlarge. So I now wonder if there is some connection to the plastics and rubbers in some of these parts to certain fluids and/or solvents. Perhaps that’s a no-brainer.

Now...that aside, here’s another update.

When researching the KYB specifications the other day I noticed that KYB was listing a new part number for the free piston in the 09 YZs, and that the part number on the 09 CRFs was unique as well, although all of these pistons shared the same dimensions. So I ordered them up and sure enough, to the naked eye (and a set of calipers and bore mics) all of them are the same size.

So I contacted KYB about this and they replied saying that the material has been changed. No other details provided.

Can’t deny or confirm this, but to be safe, I think I’ll most likely be replacing any broken free pistons in the future with the 09 models.

That is all I have at the moment.

:)

Awesome info Dave, I don't have a KYB equipped bike at the moment but for sure thats the first thing I'll do if I get an older model.

BTW the only fork oil I have found that works like it supposed to is the Honda HP5W that you can get from the dealer. All other oils either break down quickly or don't provide adequate lubrication between the slider/tube bushing.

I'm sure your oil works just as well but I go through so much of it I need a close supply (dealer 5 mins away).

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Dave,

Here is an experiment for you. Take the broken free piston and warm it up with a heat gun and see if the plastic yellows.. It may not be chemical interaction but a thermal reaction. Depending on the plastic heat can make them brittle.

I do remember the whole WP fork seal problem but I also noticed out of the 3-4 Kyb forks I've worked on that stock fluid gets very tacky to the point that it feels like binding. Just the other month I pulled apart some KLX forks and the oil was molasis that came out (30ish degrees out that day) but the Motorex I replaced it with flowed as expected. I've also found FC fluid to be thick and tacky after a short period of abuse.

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sorry active, but that comment doesn't bring us any further

might be funny for you but those of us, who want to learn, are not interested in a personal dispute between you and you know whom

So why not share your wizdom :)

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sorry active, but that comment doesn't bring us any further

might be funny for you but those of us, who want to learn, are not interested in a personal dispute between you and you know whom

So why not share your wizdom :)

Well...that got yanked nice and fast. :banghead:

Someone behind the curtain is doing their job.

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i know what you're meaning and i agree on most of it. I do this business for a living as well and it's still fun (ok, kind of :) )

Regarding the broken piston, i haven't seen yet one life nor have i heard of any here in Germany.

Maybe i'm playing in the wrong league...

That's why i try to learn and get info from every source available.

If you don't want to share your hard earned knowledge - fair enough.

But saying 'i know why but don't tell you' is kind of a coitus interruptus

at least your clues are give an indication in which direction to think further

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Dave,

Here is an experiment for you. Take the broken free piston and warm it up with a heat gun and see if the plastic yellows.. It may not be chemical interaction but a thermal reaction. Depending on the plastic heat can make them brittle.

I do remember the whole WP fork seal problem but I also noticed out of the 3-4 Kyb forks I've worked on that stock fluid gets very tacky to the point that it feels like binding. Just the other month I pulled apart some KLX forks and the oil was molasis that came out (30ish degrees out that day) but the Motorex I replaced it with flowed as expected. I've also found FC fluid to be thick and tacky after a short period of abuse.

Yea...heat is a very good consideration.

The only thing that was interesting about this is that the yellowing was not consistent which would not make sense for something surrounded by aluminum.

But I'll run some tests and see what I can find.

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Just curious, how do i get a hold of a free piston??

Dealer tells me not listed as a seperate part just buy a complete base valve(450 bucks) he must think i am wealthy.

Rang my suspension tuner and he tells me the same thing but has had them fabricated for 200 bucks, getting better, but i thought i would explore this with you guys just to make sure there isnt another route.

Maybe supply a KYB part # to the yamaha dealer?

Seems silly that an assembly that can disassemble would not have seperate parts listed.

My dealer also tried to sell me gold valves as an option......

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You won't get it from your Yamaha dealer but have to contact someone who has Kayaba parts.

Not sure about your dealers in down under, maybe Terry Hay might help.

The Kayaba part number (at least for Europe) for the 09 floating piston is

110260000501 for Yamaha and

110260000601 for Kawasaki/Honda

If you have problems getting it drop me a line

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The feel of the plastic did not feel soft and pliable like a new piston does, but felt very brittle and sharp. Not exactly a scientific analysis, but I think you can understand how different things can feel even with the common touch.

With that, I'm noting declaring that the free pistons are breaking or cracking for one reason or another, but clearly in this case, the free pistons were experiencing some form of material degradation due to, what I assume, a contamination or a reaction, brought on by the fluid or perhaps residual solvents.

:lol:

As I've posted before, those are my thoughts, exactly. :thumbsup:

"Grey seals", huh? Gee, I wonder who that could be? :usa:

They use Showa 5wt fork oil, exclusively.

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so we are saying possibly a showa fork oil doesnt like a KYB fork? i am a little worried people are saying the Silkolene oil reacts with WP fork seals, but i use kyb seals in them anyway, is this the pro rsf? as thats a full synthetic i beleive.

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Mog it was several years ago before I got kicked of KTMtalk by the forum fascist that PMK talked about this and I can't confirm which silkolene oil it was or if its even still a problem. Perhaps a search over there might bring something to light? Unfortunately silkolene is one oil that I do have access too but have resisted using because I work on so many KTM's.

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well i use the pro rsf in the pds shocks and its working well so far.In the forks i use a cheaper oil, i bet the problem was really those bushes they had at the time, i use showa slider bushes and kyb 03 guide bushes, with kyb 48mm seals there is almost nothing left thats WP LOL.

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i

Regarding the broken piston, i haven't seen yet one life nor have i heard of any here in Germany.

maybe I'm on your ignore list so you didn't see my post about 2 years ago. mine was broken :thumbsup:

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well i use the pro rsf in the pds shocks and its working well so far.In the forks i use a cheaper oil, i bet the problem was really those bushes they had at the time, i use showa slider bushes and kyb 03 guide bushes, with kyb 48mm seals there is almost nothing left thats WP LOL.

At the time WP did have 3 DU type forks.

WP also had the leakiest seals on the planet then. This was 03 / 04.

At the time I was using Silkolene Pro RSF for everything I built. While tuning my own bike, I could not overcome this crazy stiction. For whatever reason the fluid had gone after the seals, they were exposed to no solvents. Husky had a similar problem also.

New seals, different fluid no issue. Ironically I've run the stuff in many other applications without issue.

I like the fluid and still use it, just am careful of the application.

PK

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maybe I'm on your ignore list so you didn't see my post about 2 years ago. mine was broken :usa:

You talkin' to me? You talkin' to me? You talkin' to me? Then who the hell else are you talkin' to?

You talkin' to me? Well I'm the only one here. Who the &%$#@! do you think you're talking to?

isn't that the coolest part (dialog) of the film? :thumbsup:

actually i can't remember or haven't read that's yours was broken...

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Pulled a suspension apart the other day from an 07 YZ450F that had been completely reworked and set up for a pro rider. The suspension had about 7 hours on it. The re-valve was done by a big name suspension house.

The left rod would not extend from the lug and would suck back in when I pulled it out. The required three-handed operation was used to get the fork apart.

When I got the cartridges out, the rod was sitting about half way up. Pulled the upper assembly out and of course the free piston was cracked.

However, the free piston was still intact. The cracks ran vertically from the top to the bottom, with about three to four cracks running in parallel. In addition to this, the pistons were stained yellow from about half way down to the bottom.

The cracked free piston was obviously leaking, but no fragments of the unit had come off. It was also filled with fluid and the upper o-ring and bushing had a good chunk taken out of it, (the sign of a high quality re-valve).

Needless to say, it had to be replaced.

On the other fork, the free piston was not cracked but was heavily stained as well and I would assume, was nearing the state of its twin so this too was replaced. The feel of the plastic did not feel soft and pliable like a new piston does, but felt very brittle and sharp. Not exactly a scientific analysis, but I think you can understand how different things can feel even with the common touch.

With that, I'm noting declaring that the free pistons are breaking or cracking for one reason or another, but clearly in this case, the free pistons were experiencing some form of material degradation due to, what I assume, a contamination or a reaction, brought on by the fluid or perhaps residual solvents.

The other interesting thing about this build is that they used a special low-friction seal (gray in color) that was severely binding the lower tubes. And I think what was causing this, as I've seen this before, was that their fluid, (again…making some assumptions here) was ironically, reacting with the seal much like some solvents cause rubber o-rings and the like to enlarge. So I now wonder if there is some connection to the plastics and rubbers in some of these parts to certain fluids and/or solvents. Perhaps that’s a no-brainer.

Now...that aside, here’s another update.

When researching the KYB specifications the other day I noticed that KYB was listing a new part number for the free piston in the 09 YZs, and that the part number on the 09 CRFs was unique as well, although all of these pistons shared the same dimensions. So I ordered them up and sure enough, to the naked eye (and a set of calipers and bore mics) all of them are the same size.

So I contacted KYB about this and they replied saying that the material has been changed. No other details provided.

Can’t deny or confirm this, but to be safe, I think I’ll most likely be replacing any broken free pistons in the future with the 09 models.

That is all I have at the moment.

:usa:

thanks for the update dave :thumbsup:

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Pulled a suspension apart the other day from an 07 YZ450F that had been completely reworked and set up for a pro rider. The suspension had about 7 hours on it. The re-valve was done by a big name suspension house.

The left rod would not extend from the lug and would suck back in when I pulled it out. The required three-handed operation was used to get the fork apart.

When I got the cartridges out, the rod was sitting about half way up. Pulled the upper assembly out and of course the free piston was cracked.

However, the free piston was still intact. The cracks ran vertically from the top to the bottom, with about three to four cracks running in parallel. In addition to this, the pistons were stained yellow from about half way down to the bottom.

The cracked free piston was obviously leaking, but no fragments of the unit had come off. It was also filled with fluid and the upper o-ring and bushing had a good chunk taken out of it, (the sign of a high quality re-valve).

Needless to say, it had to be replaced.

On the other fork, the free piston was not cracked but was heavily stained as well and I would assume, was nearing the state of its twin so this too was replaced. The feel of the plastic did not feel soft and pliable like a new piston does, but felt very brittle and sharp. Not exactly a scientific analysis, but I think you can understand how different things can feel even with the common touch.

With that, I'm noting declaring that the free pistons are breaking or cracking for one reason or another, but clearly in this case, the free pistons were experiencing some form of material degradation due to, what I assume, a contamination or a reaction, brought on by the fluid or perhaps residual solvents.

The other interesting thing about this build is that they used a special low-friction seal (gray in color) that was severely binding the lower tubes. And I think what was causing this, as I've seen this before, was that their fluid, (again…making some assumptions here) was ironically, reacting with the seal much like some solvents cause rubber o-rings and the like to enlarge. So I now wonder if there is some connection to the plastics and rubbers in some of these parts to certain fluids and/or solvents. Perhaps that’s a no-brainer.

Now...that aside, here’s another update.

When researching the KYB specifications the other day I noticed that KYB was listing a new part number for the free piston in the 09 YZs, and that the part number on the 09 CRFs was unique as well, although all of these pistons shared the same dimensions. So I ordered them up and sure enough, to the naked eye (and a set of calipers and bore mics) all of them are the same size.

So I contacted KYB about this and they replied saying that the material has been changed. No other details provided.

Can’t deny or confirm this, but to be safe, I think I’ll most likely be replacing any broken free pistons in the future with the 09 models.

That is all I have at the moment.

:thumbsup:

Dave, do you see any drawbacks in cnc'ing a piston up out of aluminum (anodized of course) like the Showa's.

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Dave, do you see any drawbacks in cnc'ing a piston up out of aluminum (anodized of course) like the Showa's.

Cost!

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