i just sent my forks back to my tuner as the retaining nuts backed off and the shims were floating around in my oil!!! i put them back together as a single stack and they were SX stiff. i decided the best thing to do was send them back to the tuner and have the shims stacks sorted out. the forks had 250 hours of racing on them with only forks seal, bushing and oil changes. pretty good run IMO.

my bike is a 2008 yz250 revalved for gncc style woods racing. the guys at litz racing (who are awesome guys btw) called me yesterday and said that both of the plastic oem cones were broken. they replaced them with aluminum ones. jokers were pricey!!! what part was he referring too? anybody know? he is sending the broken ones back with my forks but i am really curious what i just paid nearly $200 for!

I think he may actually be referring to the floating pistons on the KYB forks. The plastic ones are known to break, so a fix has been to either drill them, or replace them with an aluminum one.

ah ok thank you! from the inner chamber. thanks a ton. those look like they are almost worth $200! what causes the stock plastic ones to break?  i guess just pressure build up?

rodgini, on 02 May 2012 - 09:59 AM, said:

Two things lead to this.  Most common is that the seal between the piston and valve stem leaks, allowing oil to collect on top of the piston.  When the piston has not been drilled between the seals as has the one in the picture, this build up of oil increases the captive air pressure on the interior of the piston to the point where it breaks by bursting outward.

The second cause occurs if the ICS spring is shimmed excessively so that it coil binds late in the compression stroke.  If this is done to the point that it prevents the bleed port from opening, internal cartridge pressures may break the piston when the fork nears bottom.

grayracer513, on 02 May 2012 - 12:31 PM, said:

ah ok makes sense. would having these broken in my forks cause a bit of oil mist to come out the bleeder button when i push it? i noticed that recently and was curious as it never did that before.

now having them fixed what kind if performance gain should i notice? they must have been like that of a while? who knows lol?? thanks gain for the info fellas!!! really appreciate it.

With the pistons broken, damping performance will suffer from air mixing with the oil.

Is the spring preload the same on the metal free piston as to the plastic one ?

rodgini, on 02 May 2012 - 12:38 PM, said:

The mist you refer to is from the outer chamber not the inner and is quite normal.

The dimensions are all the same except the aluminum piston doesn't have a groove for an upper seal.  There's no purpose for it with the cutouts or holes.

grayracer513, on 02 May 2012 - 12:31 PM, said:

thats what I think, too. so my question, can you get only the seal for a good price?
if not, you can also buy a new free piston, which I think the seal is included. in this case it doesn't matter if the old free piston is cracked or not...

Yes, you can get any of the individual seals in the fork separately, but not all of them are available from Yamaha.  For a lot of stuff, you have to go through a KYB dealer like SMART Performance.

Race Tech sells the anodized aluminum piston assemblies with seals, ready to install for $120 a pair. The OEM replacements aren't much, if any cheaper. You can get the seals separate but if the piston is already broken, the seals won't help you.