Kyb free pistons

Ichnusa
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Ichnusa
Hello, I have a 22 yz250f and i played with oil level but i have a doubt can oil be trapped in free piston chamber?
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FGR01
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FGR01 5/2/2022 5:24am
5/2/2022 5:24am
Yes it can. If you add oil through the air bleed holes it will be trapped in the free piston chamber.
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Ichnusa
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Ichnusa 5/2/2022 5:40am
5/2/2022 5:40am
How can i drain it out?
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FGR01 5/2/2022 11:37am
5/2/2022 11:37am
You have to take the forks apart, remove the inner damping cartridges, tilt them over and drain/blow the excess oil out of the weep holes on the side of the free piston chamber.

Since you're that far in, it makes sense to just drain, refill, and rebleed the inner cartridges to make sure they are right.

Then you can set the outer chamber oil volume where you actually wanted it in the first place. Smile
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Ichnusa
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Ichnusa 5/2/2022 11:52am
5/2/2022 11:52am
There is an oring in the top of the free piston how can the oil drain out?

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Ichnusa
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Ichnusa 5/2/2022 12:04pm
5/2/2022 12:04pm Edited Date/Time 5/2/2022 12:07pm
I read in the internet that from the 2018 the kyb free pistons are vented is it true? If it is the pistons should drain the oil automatically
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FGR01 5/2/2022 12:09pm
5/2/2022 12:09pm
If you put oil in the bleed hole, that oil is above the free piston, not below it. So the o-ring on the free piston is not going to retain the oil inside the upper cartridge.

Truth be told, just be riding normally, as the forks compress, any oil above the free piston is going to get forced out of the weep holes and then into the outer chamber, raising the outer chamber oil volume (as I think you originally intended). The issue is, depending on how much oil is above the free piston, you could create a hydraulic lock condition if you do big compressions with the fork before the oil can oil be forced out the little weep holes.
Ichnusa
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Ichnusa 5/2/2022 12:28pm
5/2/2022 12:28pm
If it drains automatically during the normal use it has already do it because I have rode the bike some hours yet. But my proboem is: i bought this bike brand new and beacuse the fork was harsh fro the middle of the stroke i drain 15cc of oil from the air bleed screw i ride the bike and it was too soft so with 5cc increments i have reinserted 10cc of oil and the bike becamed perfect it bottoms lightly when i overjump 2 jumps ofbmy local track but it doesn't hurts me. I decided to try softer springs but they don't like me so i put back stock springs with a 5cc lower than stock oil level like was before i changed with softer springs but the bike felt again harsh from middle and not goes thru all the stroke so i drain out another 10 cc but this time not from the air bleed but from the outer cap the bike is better but still not sufficent so i drain other 10cc but still not sufficient and i don't understand why now the level is 20cc lower but the bike still not be like before i changed with softer springs.
I'? Confused
Sorry for the long answer XD
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FGR01 5/2/2022 4:49pm
5/2/2022 4:49pm
Excess oil in the top of the free piston chamber (inner chamber) can create harshness. That is the hydraulic lock situation I mentioned. In order for oil to be drained from the bleed screw, it has to first go from the outer chamber, in the weep holes, to the inner chamber, and then out the bleed. So, I suspect you turned the forks upside down to accomplish this, but after the small draining you ended up with some oil in the inner chamber, at least for some time until it worked out.

So, the only way to ensure you get no excess oil in the inner chamber is to undo the entire top cap and either drain or add oil directly to or from the outer chamber. Trying to add or drain from the bleed screw complicates and confuses the process.

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