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2017 SSS Forks free piston still need to be drilled?

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Hello,

Just wondering if anyone has had their forks apart on a 2017 model bike. Does the plastic free piston still need to be drilled to eliminate the issue with it cracking if the upper seal leaks? 

thanks!

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I've got the 2016 250x and never did mine.  I'm at about 115 hrs and did my second re-build/revalve and they looked good.  The suspension forum would probably get you a fast answer on this.  

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40 minutes ago, Monk said:

It's still plastic, it still should be drilled... 

My tuner said he has seen some broken from a brand new bike that was never ridden.... so yes drill them.

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52 minutes ago, Wrfrk said:

What is this you are speaking of... YZ newb here!

Go to around 7 minute mark

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How do they not do this at the factory!? I'm re springing bike, so i'll have it apart, might as well do it while I'm in there. I'm guessing new ones are not that cheap!

Thanks again!

 

 

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^^^^^^ What he said? ^^^^^^

 

Wonder if just adding some fork bleeders and releasing the pressure would solve this without going through all that........

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I'm no suspension expert but rather an enthusiast who does his own revalving 

and likes to learn about such stuff, this is my understanding of how it functions.

 

Commonly regarded as twin chamber / closed cartridge forks, by design the KYB 'SSS' actually has 3 separate chambers.

(the outer tube, the inner cartridge and inside the ICS piston's cavity)

 

The stock KYB ICS piston/cavity isn't vented (to differ from a Showa patent we've often read)

so in some specific conditions that chamber can overpressure and crack the plastic pistons.

The problem isn't from gradual pressure build-up that could preventatively be vented but rather from hard impacts and sudden increases of pressure.

On pretty much equivalent Showa TC47 fork design, they rather have very short pistons and only a single o-ring at the bottom,

making Showa's ICS cavity 'common' with the outer fork chamber, so no differential in pressure / sudden build-up.

 

Performance wise, in theory the slight increase in pressure in the KYB's ICS chamber might  add to the force of the ICS spring,

increasing the pressure in cartridge to prevent cavitation on big impacts, but I've not read about that anywhere.

 

When you drill a KYB plastic piston, the 3rd 'ICS' chamber is now made common with the outer chamber,

equalizing the pressures on both inner and outer sides of it and preventing damage.

Doing so also slightly increases the outer chamber's air volume, so equal to reducing the oil volume as well.

(it was once mentioned about 30cc of oil is required to compensate for the added air volume)

 

I preventatively replaced mine with aftermarket aluminium pistons during my 1st YZ125 fork servicing (seals, bushings, oil)

Despite quite a few hard landings, the OEM ones weren't damaged at all.  (for sale BTW, Canada only, sorry no cross-border shipping)

With what I've read over the years, simply drilling the OEM ones and removing the top o-ring would have been just as good and, free!

 

Italy's TM Motorcycles use KYB forks, despite all the fancy components those bike come with as stock equipment,

those forks still use plastic ICS pistons of TM's own proprietary design (no top o-ring).

If there were any advantage to using aluminium ones, I believe TM would have done so.

 

Edited by mlatour
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1 hour ago, Wrfrk said:

^^^^^^ What he said? ^^^^^^

 

Wonder if just adding some fork bleeders and releasing the pressure would solve this without going through all that........

No

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1 hour ago, mlatour said:

I'm no suspension expert but rather an enthusiast who does his own revalving 

and likes to learn about such stuff, this is my understanding of how it functions.

 

Commonly regarded as twin chamber / closed cartridge forks, by design the KYB 'SSS' actually has 3 separate chambers.

(the outer tube, the inner cartridge and inside the ICS piston's cavity)

 

The stock KYB ICS piston/cavity isn't vented (to differ from a Showa patent we've often read)

so in some specific conditions that chamber can overpressure and crack the plastic pistons.

The problem isn't from gradual pressure build-up that could preventatively be vented but rather from hard impacts and sudden increases of pressure.

On pretty much equivalent Showa TC47 fork design, they rather have very short pistons and only a single o-ring at the bottom,

making Showa's ICS cavity 'common' with the outer fork chamber, so no differential in pressure / sudden build-up.

 

Performance wise, in theory the slight increase in pressure in the KYB's ICS chamber might  add to the force of the ICS spring,

increasing the pressure in cartridge to prevent cavitation on big impacts, but I've not read about that anywhere.

 

When you drill a KYB plastic piston, the 3rd 'ICS' chamber is now made common with the outer chamber,

equalizing the pressures on both inner and outer sides of it and preventing damage.

Doing so also slightly increases the outer chamber's air volume, so equal to reducing the oil volume as well.

(it was once mentioned about 30cc of oil is required to compensate for the added air volume)

 

I preventatively replaced mine with aftermarket aluminium pistons during my 1st YZ125 fork servicing (seals, bushings, oil)

Despite quite a few hard landings, the OEM  ones weren't damaged at all.  (for sale BTW, Canada only, sorry no cross-border shipping)

With what I've read over the years, simply drilling the OEM ones and removing the top o-ring would have been just as good and, free!

 

Italy's TM Motorcycles use KYB forks, despite all the fancy components those bike come with as stock equipment,

those forks still use plastic ICS pistons of TM's own proprietary design (no top o-ring).

If there were any advantage to using aluminium ones, I believe TM would have done so.

 

Essentially when drill and remove the upper o-ring, you make the forks into a twin chamber unit... 

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this there any disadvantage to just drilling and leaving the o-ring in case it leaks to stop the cartridge from cracking? Alternatively, is there an advantage to pulling top o-ring?

thanks again!

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Wow this is a HUGE chink in the SSS armor I've heard all about........ WP never has these issues!

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Advantage or not, the top o-ring would not have much use once the piston is drilled,

there are bushings on the piston so it doesn't rely on the o-rings to center it inside the cartridge's bore.

Comparatively Showa pistons are very short (only about 1" high versus the 3" KYB's)

and only have one o-ring at the bottom but two rows of rather wide bushings.

 

I'd think that removing the o-ring would decrease the chances of pressure build-up even more and of oil getting trapped in the cavity.

Holes now make it a true dual chamber design, if the forks are ever laid over on their sides or inverted

 it transfers some outer chamber oil thru the cartridge purge hole into the ICS spring's cavity via the piston holes.

That oil has to drain out not to 'hydrolock' the ICS piston.

 

SDI Elite aftermarket aluminium pistons don't have any top o-rings either.

 

Quoted: "leaving the o-ring in case it leaks" ,  

not sure what you meant, in case what leaks?

Edited by mlatour

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3 hours ago, Wrfrk said:

Wow this is a HUGE chink in the SSS armor I've heard all about........ WP never has these issues!

One time in history WP apparently makes a decent fork, so forget all those SHITTY AS F*%$ forks for decades and roll on here talking big. SEIZE THE MOMENT!!

 

Now, back to talking about things as normal. Some break and some do not. To each his own.

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:) I was just being a smart a$$  .... but I am actually disappointed to find this out... :( 

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It's not a big deal. I flat landed the CRAP out of my heavy SSS-equipped WR450 many a time before I got around to taking the forks apart. Pistons were not broken. I drilled just to be on the safe side (few years ago now) because I believe what I read on here sometimes - if you're changing oil anyway, it's an additional 5 minutes at most. Recommend putting the holes at the very bottom of the piston so any trapped fluid can drain out. Super easy mod that I wouldn't go out of my way for.

I wouldn't call it a chink in the armor, so much as a way to improve the reliability of the forks. Although it has no functional impact to the performance.

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What is the effect on the suspension feel if those chambers are cracked?

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