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KYB SSS - components wear, aftermarket free piston bleeding procedure

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Hello.
Again I'm asking for Your help. I've disassembled mys front YZ 125 '08 forks. I've found some wearing in two components. First  is the free piston bushing - take a look. The second is the damper rod. It looks like something is bent but I measured the inner tube and the damper assembly with dial indicator and V blocks - they are pretty straight (0,04 and 0,05mm). So i wonder if it's not caused by debris inside in the past. The third thing is the free piston itself. I've learned that i got some aftermarket one. I know that it's popular to modify stock ones by drilling holes in them to prevent them form blowing. But i do not fully understand what my free piston give (or take) in performance of my suspension and most important - if bleeding procedures are the same - I've done bleeding of one side, the damper extends fully but i found an information that it's not necessarily what it should look like - http://www.smartperformanceinc.com/YZMODASSEM.htm

So to sum up - my questions:
1. Can I assemble free piston with bushing in this condition ? If not, where can i get spare one ? Is it the same as one stock ?

2. What about damper rod ? Is it reusable ? There are no way i can get spare one - even yamaha OEM doesn't have them. What may have caused this wear ?

3. What are the bleeding procedures for this kind of free piston ? Should the damper rod extend fully ? The site I linked above says it should NOT... Is the Yamaha manual procedure good for this one ? How does this kind of piston influence performance of my suspension ?

Hail to the TT community. I'd be finished withou Your support. Thanks !

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Edited by Stigy

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There are actually very few suspension parts available thru Yamaha

most of them sold as complete 'assemblies' which are quite expensive.

 

Individual parts are available from Technical Touch, pretty much any item you need.

 

By memory the stock plastic ISC piston uses a similar bushing but unsure if it's the same size as that aftermarket piston.

 

Cartridge bleeding procedure is the same, the piston's inner bore is now vented to the outer tube, increasing the volume

so some have suggested adding a bit more oil to the outers to compensate.  

Edited by mlatour
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Thanks Mlatour ! That can help a lot. I'm still considering putting it back as it is. I'm wondering what has caused this damper rod wear. I'm afraid to a waste new one :( The main inner tube bushing is perfect. I suspect one of previous owners might ride with bushing wear down, which caused free play and that caused damper rod wear... Anybody to support this theory ?

Also - I'm still not sure if damper rod should extend fully - the info I linked above suggest that with this mod it shouldn't...

Edited by Stigy

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Recent discussion here suggests that if the rod fully extends out by itself after bleeding the cartridge, you may have an air pocket left inside:

 

I have both KYB and the very similar Showa 47 TC forks on my bikes,

neither of them fully extend all the way out when purged of excess oil,

stopping about 50mm from full travel.

 

The only time I got more extension was when experimenting with ICS spring preload and that wasn't successful.  

 

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That's weird. The manual states clearly - if damper assembly not fully stretched - repeat the process... How is that ?

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Years ago @DaveJ posted very smart explanation of this subject. I'll allow myself to quote it:
"This might help as there are three states of where these cartridges can fall into.

1. Rod fully extended - Free-piston has no play, free-piston has zero pre-load. Cartridge has zero air. This is ideal. Note that the rod will not fully extend on its own as pressure from the free-piston and spring is not great enough to over-come the static friction of the seals within the last 10 to 20mm of movement. Therefore you have to pull the rod out and verify that it does not get sucked back in.

2. Rod is fully extended. Free-piston has play, (slack) free-piston has zero pre-load. This means there is air within the cartridge. Rebuild it. Usually in this state, the rod will suck itself back in when brought out to full extension.

3. Rod is fully extended. Free piston has no play, free-piston spring has pre-load. This is a positive charge and means that there is too much fluid, and most likely some air, within the cartridge. Bleed the excess fluid by fully compressing the rod (with the jam nut in place) with the cartridge at an angle (to move air up and out). Then test for condition noted in number 1. "

That's the best explenation i found on the internet so far. Thanks @DaveJ !

Also @mog suggested to check your job by turning the champer upside down and pump the rod full stroke, that's also a good advice.

On the other hand I  found @homo erectus post where he claims:
"Other than the '05 POS AOS cartridge, every one I do extends all the way back after being fully compressed. If you have too much oil to start with it will pull in air when you blow it off and not extend all the way. I have fond over the years if the cartridge starts to blow off with more than about 1" of rod left, it will not extend back all the way."

And that's my case. When I used too much oil it didn't extend. When I used correct amount (measured it with a device, exactly with service manual spec -148mm) the rod fully extended.

Damn... that's a hard thing to clarify...

As for the rest can anybody suggest If i can re use the damper rod and free piston bushing ? I'm still not sure if they are no go for further use.

Edited by Stigy
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2 hours ago, Stigy said:

Years ago @DaveJ posted very smart explanation of this subject. I'll allow myself to quote it:
"This might help as there are three states of where these cartridges can fall into.

1. Rod fully extended - Free-piston has no play, free-piston has zero pre-load. Cartridge has zero air. This is ideal. Note that the rod will not fully extend on its own as pressure from the free-piston and spring is not great enough to over-come the static friction of the seals within the last 10 to 20mm of movement. Therefore you have to pull the rod out and verify that it does not get sucked back in.

2. Rod is fully extended. Free-piston has play, (slack) free-piston has zero pre-load. This means there is air within the cartridge. Rebuild it. Usually in this state, the rod will suck itself back in when brought out to full extension.

3. Rod is fully extended. Free piston has no play, free-piston spring has pre-load. This is a positive charge and means that there is too much fluid, and most likely some air, within the cartridge. Bleed the excess fluid by fully compressing the rod (with the jam nut in place) with the cartridge at an angle (to move air up and out). Then test for condition noted in number 1. "

That's the best explenation i found on the internet so far. Thanks @DaveJ !

Also @mog suggested to check your job by turning the champer upside down and pump the rod full stroke, that's also a good advice.

As for the rest can anybody suggest If i can re use the damper rod and free piston bushing ? I'm still not sure if they are no go for further use.

If you search around he also has an updated bleed procedure that it way better then the manual  including taping the bleed holes up it works every time. 

MM 

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3 hours ago, Stigy said:

On the other hand I  found @homo erectus post where he claims:
"Other than the '05 POS AOS cartridge, every one I do extends all the way back after being fully compressed. If you have too much oil to start with it will pull in air when you blow it off and not extend all the way. I have fond over the years if the cartridge starts to blow off with more than about 1" of rod left, it will not extend back all the way."

And that's my case. When I used too much oil it didn't extend. When I used correct amount (measured it with a device, exactly with service manual spec -148mm) the rod fully extended.

Right. But as i said above, I'm not fully convinced. Homo erectus got a good point here. I was wondering lately why do manuals always recommend some oil level for inner chambers. It doesn't matter because the excessive will flow out through bleeding holes, right ? But apparently the oil level could matter. Why would they recommend it otherwise ? If Homo erectus is right, and apparently he could be (in my case that was 100% the case) it might be an answer. But for now i can't understand how can the air be pulled in when blowing off the chamber ?

Any opinion on damper rod wear anyone ?

Edited by Stigy

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