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Kyb SSS cartridges not releasing excess oil

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My 2008 yz250 forks have been harsh on logs and roots since I've owned it.  So I removed the cartridges and found the dampening rod was harder to push in than normal and also extended with force to the end of travel, so rebuilt the cartridge and found nothing wrong with the ics or any seals or bands.  Once rebuilt and the rod bottomed the rod is normal stiffness and extends to right at the end but just barely as it should.   I used 300ml in the outer chamber and went riding.  They worked great for an hour or so but then harsh again.  I pulled the cartridges and found the same thing rod extending with force.  I would say the carts are taking in oil through the seal head and not bleeding enough from the ics holes.  Any ideas why this is happening?  Couple of notes, first the ics Pistons are not drilled.  Maybe drilling them would help with this. Second, the dampening rod does have some side to side movement as in possibly the bushing is worn, but the seal seems to be fine as there is no oil getting out of the cartridge and they have no air in them.

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On similar Showa TC47's, it's often been mentioned that when the ICS piston inner seal is worn,

the rod gets 'sucked' back into the cartridge nearing full extension.

Sounds similar to your issue, perhaps you are feeling the resistance of vacuum while extending the rod.

 

Like you my CRF's Showa cartridges would bleed perfectly during initial re-assembly but the dampening would turn to mush after only one ride. 

Additionally, internal 'sloshing' of the oil could be heard/felt when cycling the rod upon dis-assembly.

Replacing the ICS piston inner seals and lower cartridge rod seals did the trick.

Edited by mlatour
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My cartridges aren't losing dampening, more like too much.  Seems like they are taking in oil but not releasing it when the ics piston moves back.  They have 1.6kg ics springs that are 107mm long.  After I bleed the carts, the top piston band is just barely visible through the bleed holes and the rod feels normal.  When they get harsh the piston is higher up, preloading the ics spring and the rod extends forcefully all the way to the end I stead of slowing down and stopping just short of the end like it should. 

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