WP CC Fork pressure build up


94 replies to this topic
  • yamaha227

Posted February 16, 2012 - 03:38 PM

#1

Asked this question on ktmtalk but got nothing....

Wondering if anyone has some ideas or mods/fixes etc to decrease pressure build up in the WP CC forks.
Noticed everytime i pull my forks down for a service/shim change, i check the bladder pressure before i release it and its up to 22psi, I normally set it at 16psi during assembly. I also normally fully compress the damper rod in before disassembly to check no air has entered the cart during operation on the bike... a fair amount of oil comes out the relief/poppet valve. So this increase in oil volume into the cart during operation must be bumping up the bladder pressure?
I cant imagine this is good for fork performance and consistency, or is this just what they do and a transfer that happens to balance internal pressure/volumes out? Would it be worth while re-setting bladder pressure after the first 1 or 2 decent rides to the desired pressure or will it just build up again?

  • mog

Posted February 16, 2012 - 03:45 PM

#2

Its probably normal and it might be the transfer of oil from outer to inner chamber, you could reset it after a ride and see if it carries on

  • chadman300

Posted February 19, 2012 - 12:46 PM

#3

Asked this question on ktmtalk but got nothing....

Wondering if anyone has some ideas or mods/fixes etc to decrease pressure build up in the WP CC forks.
Noticed everytime i pull my forks down for a service/shim change, i check the bladder pressure before i release it and its up to 22psi, I normally set it at 16psi during assembly. I also normally fully compress the damper rod in before disassembly to check no air has entered the cart during operation on the bike... a fair amount of oil comes out the relief/poppet valve. So this increase in oil volume into the cart during operation must be bumping up the bladder pressure?
I cant imagine this is good for fork performance and consistency, or is this just what they do and a transfer that happens to balance internal pressure/volumes out? Would it be worth while re-setting bladder pressure after the first 1 or 2 decent rides to the desired pressure or will it just build up again?

Don’t adjust bladder pressure, Release inner cartridge pressure than your bladder pressure will go back to 16 psi.
When the inner cartridge pressure rises the forks get really harsh.
With that new updated cartridge seal, The forks
pump up faster. I wish KTM would address and fix this issue

Edited by chadman300, February 19, 2012 - 12:47 PM.


  • chadman300

Posted February 19, 2012 - 01:03 PM

#4

From Slavens Racing


Closed chamber bladder forks only

Besides the usual harshness, deflection, and spring rate issues, the WP closed chamber bladder fork has a pressure build-up issue that is very labor intensive to correct. This service is HIGHLY RECOMMENDED for ALL applications, especially when competing in events that require non-stop riding for 2-3 hour periods. Under these conditions increased stiffness and deflection will be experienced from pressure build-up in the inner cartridge and outer chamber and in extreme cases and conditions the fork becomes rigid and un-rideable. Manual bleeding of the air from the outer chamber does not cure the problem. 

This service is only available at Slavens Racing. Developed by Jeff Slavens and Kelvin Thomas

http://slavensracing...ension-services

Edited by chadman300, February 19, 2012 - 01:04 PM.


  • yamaha227

Posted February 20, 2012 - 05:58 PM

#5

From Slavens Racing


Closed chamber bladder forks only

Besides the usual harshness, deflection, and spring rate issues, the WP closed chamber bladder fork has a pressure build-up issue that is very labor intensive to correct. This service is HIGHLY RECOMMENDED for ALL applications, especially when competing in events that require non-stop riding for 2-3 hour periods. Under these conditions increased stiffness and deflection will be experienced from pressure build-up in the inner cartridge and outer chamber and in extreme cases and conditions the fork becomes rigid and un-rideable. Manual bleeding of the air from the outer chamber does not cure the problem. 

This service is only available at Slavens Racing. Developed by Jeff Slavens and Kelvin Thomas

http://slavensracing...ension-services


Thats the kind of thing im talking about. I would have thought more people would be looking into this problem or have a fix for it as it causes quite a noticable change in the forks feel/performance.

Wonder what slaves actually do in there?

  • DaveJ

Posted February 21, 2012 - 08:15 PM

#6

Asked this question on ktmtalk but got nothing....

Wondering if anyone has some ideas or mods/fixes etc to decrease pressure build up in the WP CC forks.
Noticed everytime i pull my forks down for a service/shim change, i check the bladder pressure before i release it and its up to 22psi, I normally set it at 16psi during assembly. I also normally fully compress the damper rod in before disassembly to check no air has entered the cart during operation on the bike... a fair amount of oil comes out the relief/poppet valve. So this increase in oil volume into the cart during operation must be bumping up the bladder pressure?
I cant imagine this is good for fork performance and consistency, or is this just what they do and a transfer that happens to balance internal pressure/volumes out? Would it be worth while re-setting bladder pressure after the first 1 or 2 decent rides to the desired pressure or will it just build up again?



If it's an 07 to 09 fork you should update the seal head via the following parts.

48600760S
48600829

Simple as that.

  • Adammoto

Posted February 21, 2012 - 10:06 PM

#7

Ben, the pressure build up you've been getting seems out of line with what others are experiencing. Maybe there's something else going on.
Are you getting the same issue on both bikes?
Remind me what years/makes/models your bikes are.
What's your method for bleeding the cartridge?
How do you remove and re-install the damper rod from the cartridge? Teflon tape & grease on the threads? Any chance those very delicate cartidge seals got damaged?

Just looking at possibilities here.

  • yamaha227

Posted February 21, 2012 - 10:36 PM

#8

If it's an 07 to 09 fork you should update the seal head via the following parts.

48600760S
48600829

Simple as that.


Already have updated cart seal head an purple skf cart seals. (2012 oem parts). Ive heard you do a mod to a stiffer cart/poppet relief spring?

Ben, the pressure build up you've been getting seems out of line with what others are experiencing. Maybe there's something else going on.
Are you getting the same issue on both bikes?
Remind me what years/makes/models your bikes are.
What's your method for bleeding the cartridge?
How do you remove and re-install the damper rod from the cartridge? Teflon tape & grease on the threads? Any chance those very delicate cartidge seals got damaged?

Just looking at possibilities here.


Only running one bike with CC forks.
2012 350 EXCF, with 08 WP CC forks, update cart seal head & seals, update outer oil seals and bushings.
Teflon tape when removing damoer rod, but generally if getting access to MV, i just clamp the inner cart and undo the whole seal head and leave it on the shaft. (saves possibility of damaging cart seal) Sound ok? inner cart seals are 10 hours old.

Bleed method: assemble innner cart, fill to 3 inchs approx below top, stroke damper rod 10 times approx slowly until no more bubbles, let it sit for 10min. Add 1psi approx to bladder until its a full uniform shape and not collapsed in. install bladder/comp assembly letting it drop slowly into cart as excess fluid overflows. Do up bladder/comp assembly. charge bladder to 30psi approx whilst cart is still vertical in vice. stroke damper rod 3 times about 2-3 inchs each time and let return by itself (to push any trapped air to the top), set bladder pressure to 16 psi. re-clamp inner cart at approx 45 degree angle with relief poppet facing up, stroke damper rod fully in and hold it while just cracking poppet to release anymore trapped air until clear fluid comes out. release rod, check it extends fully on its own..... thats it.... Thoughts?

  • mog

Posted February 22, 2012 - 12:32 AM

#9

I would bleedit at least 2 times when open, and I don't crack the poppet at all

  • yamaha227

Posted February 22, 2012 - 01:22 AM

#10

I would bleedit at least 2 times when open, and I don't crack the poppet at all


What do you mean 2 times when open?

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  • mog

Posted February 22, 2012 - 04:39 AM

#11

Stroke the rod, leave for 10 minutes, stroke the rod leave for 10 minutes, and I would do that once more to be honest

  • Adammoto

Posted February 22, 2012 - 07:20 AM

#12

Already have updated cart seal head an purple skf cart seals. (2012 oem parts). Ive heard you do a mod to a stiffer cart/poppet relief spring?



Only running one bike with CC forks.
2012 350 EXCF, with 08 WP CC forks, update cart seal head & seals, update outer oil seals and bushings.
Teflon tape when removing damoer rod, but generally if getting access to MV, i just clamp the inner cart and undo the whole seal head and leave it on the shaft. (saves possibility of damaging cart seal) Sound ok? inner cart seals are 10 hours old.

Bleed method: assemble innner cart, fill to 3 inchs approx below top, stroke damper rod 10 times approx slowly until no more bubbles, let it sit for 10min. Add 1psi approx to bladder until its a full uniform shape and not collapsed in. install bladder/comp assembly letting it drop slowly into cart as excess fluid overflows. Do up bladder/comp assembly. charge bladder to 30psi approx whilst cart is still vertical in vice. stroke damper rod 3 times about 2-3 inchs each time and let return by itself (to push any trapped air to the top), set bladder pressure to 16 psi. re-clamp inner cart at approx 45 degree angle with relief poppet facing up, stroke damper rod fully in and hold it while just cracking poppet to release anymore trapped air until clear fluid comes out. release rod, check it extends fully on its own..... thats it.... Thoughts?


Ben, everything you've done including bleed method sounds perfect. I wish I had a better answer for you.

By the way, I've tried stiffer springs on the pin valve, but I don't think this is a real fix for pressure build up. Think about it - a stiffer spring just makes it harder for the excess fluid to escape. The problem is caused by fluid being pushed into the cartidge past the seal.

I have a couple ideas I can try but it will take some testing. I'll get back to you.

  • suhoi27

Posted February 22, 2012 - 09:43 AM

#13

...a recent "design change" oriented thinking led me to the conclusion that cart. seal is TOO close to the bottoming device....TTX has another view-there is a large distance + some relief orifices, located between the bottoming "piston" (the so called "[size="2"][color="black"]CHECK VALVE STOP ") [/color][/size]and the seal. My recent experience with installing a Cone Valve "kit" into regular WP CC fork showed that "it might be enough space" to redesign the "screw sleeve" making it longer+ relief orifice. It will also require a redesign of the cart. rod, just to keep the existing stroke.....Sure, I am too lazy for now!.....I am not quite aware of the MXT design, but I suspect its tunability is the key for a reduced "back flow" to the cart....

  • DaveJ

Posted February 22, 2012 - 01:04 PM

#14

Already have updated cart seal head an purple skf cart seals. (2012 oem parts). Ive heard you do a mod to a stiffer cart/poppet relief spring?



Yes, we change to a different material on the o-ring and run a stiffer spring.

We also fill the cartridge to the brim, add about 2 PSI to the bladder, and we bleed the base piston before allowing the base assembly to fall into place.

And we run our pressures between 22 to 24PSI. Have not seen any issue of mixing or pressure changes with this set-up and process.

  • dwb79

Posted February 22, 2012 - 02:40 PM

#15

Ben, did you have this problem before updating the seal holder and seal?

Adam, I'd have to agree. A stiff pressure relief spring would only allow the cartridge to build up even more pressure before dumping excess.

DaveJ, could it be that your oil is less likely to work past the cartridge seal during bottom out situations?


It could all be fixed if we can isolate the cartrdige seal from the pressurised oil in the bottoming cone when the cartrdige enters near full travel. The cartrige seal, like most seals, is designed to primarily work in one direction and in this case it is to keep the oil in the cartridge, not to stop oil entering the cartridge. Could the newer seal holder be machined to accept a second seal installed upside down? :bonk: Two of the new seals would still offer much less stiction than the old seal.

This is what the Slavens website says, "Proprietary cartridge, stanchion tube, and HL ring machining to reduce pressure balance issues". What do you think they mean by HL RIng?

  • yamaha227

Posted February 22, 2012 - 03:01 PM

#16

Ben, everything you've done including bleed method sounds perfect. I wish I had a better answer for you. By the way, I've tried stiffer springs on the pin valve, but I don't think this is a real fix for pressure build up. Think about it - a stiffer spring just makes it harder for the excess fluid to escape. The problem is caused by fluid being pushed into the cartidge past the seal. I have a couple ideas I can try but it will take some testing. I'll get back to you.


Thanks adam, let me know if you find anything.

Yes, we change to a different material on the o-ring and run a stiffer spring. We also fill the cartridge to the brim, add about 2 PSI to the bladder, and we bleed the base piston before allowing the base assembly to fall into place. And we run our pressures between 22 to 24PSI. Have not seen any issue of mixing or pressure changes with this set-up and process.


Maybe charging to 22-24psi helps pressurize the inner cart oil more equaling more internal pressure on the cart seal lip stopping it from letting as much outer chamber oil in? Maybe my initial charge of 16psi isnt enough for these new updated low drag skf cart seals....but i thought 1.2 bar was the WP rec setting, 16psi isnt far off that.

Ben, did you have this problem before updating the seal holder and seal? Adam, I'd have to agree. A stiff pressure relief spring would only allow the cartridge to build up even more pressure before dumping excess. DaveJ, could it be that your oil is less likely to work past the cartridge seal during bottom out situations? It could all be fixed if we can isolate the cartrdige seal from the pressurised oil in the bottoming cone when the cartrdige enters near full travel. The cartrige seal, like most seals, is designed to primarily work in one direction and in this case it is to keep the oil in the cartridge, not to stop oil entering the cartridge. Could the newer seal holder be machined to accept a second seal installed upside down? :bonk: Two of the new seals would still offer much less stiction than the old seal. This is what the Slavens website says, "Proprietary cartridge, stanchion tube, and HL ring machining to reduce pressure balance issues". What do you think they mean by HL RIng?


Some good ideas there dave, will have forks apart early next week for a service and investigation... maybe the older style seal is more reliable in this department?

Only ever road with these forks once with the older style seal/seal head before i stripped them down and updated/revalved them etc so never paid attention to it...

Have no idea what slavens is talking about, anyone got ideas??

Dont think i have mentioned on here yet, another thing i have noticed is im not using the last inch of fork travel very often at the moment, just been practicing on my special tests that dont have any big mx jumps or "holy shit" G-outs etc.... definately still rough though with some big holes etc. So maybe the carts arent getting the oppotunity to purge the excess oil out as often as they should?

As dave (dwb79) has mentioned to me though, i think its a good idea to have this last inch still avail as a safety margin/buffer though as when i start racing again for the year in a few weeks im sure i will find a use for it....

Edited by yamaha227, February 22, 2012 - 03:05 PM.


  • yamaha227

Posted February 22, 2012 - 03:21 PM

#17

Some pics, thanks to sean...

Differences between 08 outer tube and >09 tubes. Wonder what those 2 additional lower machined rings are for?

Posted Image

Showing top of inner cart, the lower groove i think is maybe one of the things slavens mods???

Posted Image

  • chadman300

Posted February 23, 2012 - 01:17 AM

#18

Some pics, thanks to sean...

Differences between 08 outer tube and >09 tubes. Wonder what those 2 additional lower machined rings are for?

Posted Image

Showing top of inner cart, the lower groove i think is maybe one of the things slavens mods???

Posted Image

That lower groove in the inner cart is ''Stock '' NOT a Slavens mod

  • suhoi27

Posted February 23, 2012 - 05:20 AM

#19

I just also checked mine 08 SX forks-the lowest picture is a stock. +1

  • 08250sxs

Posted February 23, 2012 - 06:43 AM

#20

I never stated it was a slavens mod. THe inner cart is stock. I do wonder if they would machine the groove larger. The outer tubes: one is stock (black) the other is off 09 sxs forks. i just thought i would show the difference in tubes. It was interesting to see the machined the grooves non the less and they do match up to poppet valve of the inner cart.





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