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Showa TC's, question about ICS spring length (or lack thereof)

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Hey everyone, 

i have an '06 CR250R with Showa TC's and did my first oil change (got the bike second hand 

last summer) to find a whole slew of weirdness going on inside(more on that later).  First thing I noticed is the ICS springs don't have any preload on the piston.  When the base valve assembly is removed, the piston can slide about 1/2-3/4" and springs do the same.  It struck me as weird because after filling and installing the base back in the cartridge and pumping the rod to compress it, it will not extend the last inch or two on its own.  I just replaced the damper rod seals(one was leaking so bad there was no oil for damping!  More on this later) so I don't think it's that.  And they both do it about the same.  

 

From my understanding, wouldn't this allow the fluid to cavitate from not having pressure on it at the top of the stroke?  I guess the way I'm imagining it is like a shock with no bladder pressure.  

Correct me if I'm wrong and this is ok.  Thanks

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It's all normal. When you were inserting the compress assembly, and it got hard to push in all the way and thread it in, at that point the free piston slid up the shaft and you were compressing the spring a little and there is pressure in there. It may not come out all the way due to stiction. As long as you did the bleeding correctly and installed correctly, and the rod doesn't suck itself back in after pulling it out that last inch or 2, it's all good. It usually comes out all the way until you do the last full stroke to expel the excess oil out of the inner cartridge, then that's when it has a little less pressure and doesn't go the full way out on its own. 

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Thanks for the quick answer.  Yeah, nothing else strange is happening in the cartridge mechanically(suction noises or anything, all seals look good).  

 

I've serviced several, but the only one I've been into passed oil/seal changes was a friend's '08 CRF, and I remember his piston assembly was waaay harder to push down than mine into the cartridge.  

 

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That can depend on how much extra oil is in the inner cartridge, if there isn't any extra oil in there it will thread in easy, the more extra oil there is inside the harder it is to push down and get it to start threading in, cause it's compressing that spring with too much oil in there. If you can't get it to thread in, you hold it down and push the rod up until a little oil squirts out then push the compression assembly back in while pulling the rod out and try to get it to thread in. After threaded in you pump it several times (4" from full stroke, not full stroke), then pump it to full stroke while holding it at an angle to expel excess oil and any air that was still in there. Then some forks will extend fully out on their own, some stop about an inch or 2 away from full extension. That's been my experience anyway working on lots of showas and kybs.

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On Showa TC47's, 

both bikes I've serviced ('07 & '08) had the ICS piston inner seal (piston to rod) worn,

despite the cartridges thoroughly purged of air, until those seals were replaced oil 'gurgling' sounds

were always heard and, the rod got sucked back into the cartridge when fully extending it.

 

As to the original question, some KYB 'SSS' forks use a shorter spring with a nylon spacer,

same as with longer spring designs, they don't have any preload.

Performance wise, I'm guessing you can compare it to mid-valve 'float' where the forks are allowed to conform to small

terrain imperfections with minimal dampening.

 

Aftermarket ICS springs are the same length as the Showas, so a spacer isn't required when installing them in KYB's.

I've got OEM Showa's in my YZ at the moment, and Race Tech ones in my CRF-X.

 

 

 

Edited by mlatour

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