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almostinvincible119

KYB Plastic Base Valve Piece

15 posts in this topic

I know this has been posted a while ago, but I cannot locate the thread so I am posting another question. Where can I purchase this part that has the red arrow on it. I know there used to be a guy on here who was a KYB distributor and he mentioned he could get one.

Another question, they seem to break often (from what I can remember being posted) and there was supposed to be some mod you could perform to keep them from breaking.

If you could answer or link me to the old thread, I would greatly appreciate it.

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I read somewhere, maybe the SmartPerf. site or one of those threads listed above that the metal version doesn't allow expansion thus putting pressure on the inner chamber tube and bulging it....

Anyone else see the same thing?

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I read somewhere, maybe the SmartPerf. site or one of those threads listed above that the metal version doesn't allow expansion thus putting pressure on the inner chamber tube and bulging it....

Anyone else see the same thing?

I haven't heard that, but on the surface, it already sounds like BS.

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Just having read the discussion i should point out that Kayaba made some aluminum pistons that were in some factory forks. This solved the piston breaking problem.

That was until the forks needed to be serviced. Closer inspection revealed the top section of the inner chamber had bellowed out so much that it was touching the outer tube (!)

Could air pressure do that? Or does it take hydraulic displacement to get up those sorts of pressures. Aluminum piston was OK though, it survived, just wrecked a far more expensive part. The inner seal had leaked.

This was from a noob, but who knows? Maybe someone made something like Daves design but didn't make it an open design such as he has?

Also want to point out that the inner chamber walls are pretty thick.

Post #24 on http://www.thumpertalk.com/forum/showthread.php?t=659129

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I broke that part on 1 fork about a year ago (after a huge crash) and didn't know it. I was chasing settings for weeks trying to get something to work like it should before the crash.

Thank God that part was available.

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That's an old discussion, but note that there is no indication as to whether the aluminum pistons the poster mentioned were vented between the upper and lower seal, as the ones Dave was offering are. Since KYB does not vent their plastic pistons in this manner, I would have to guess with some certainty that they were not. Then note that he stated that the inner seal had leaked. That would mean that oil from the cartridge had been pushed up into the top of the free piston, which would increase the pressure at the top of the chamber to the point where it would have caused the damage referred to at full compression. When this occurs with a plastic piston, it simply breaks it.

The reason the free piston is vented is twofold, and one of them is to prevent oil that may gather on top of the piston from hydro-locking the cartridge assembly by giving the oil a route out of the air chamber to the outer well of the fork. The other is to reduce the "air spring" influence on the inner chamber free piston, and allow cartridge pressure to be more completely regulated by the inner chamber spring(s) (ICS). With Dave's pistons opened up like this, I don't see a way for them to cause a problem of the kind discussed here.

Read:

http://www.smartperformanceinc.com/YZMODASSEM.htm

http://www.thumpertalk.com/forum/showthread.php?t=650136

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