'25 Beta 300 race edition KYB forks. I am chasing down the cause of excess air buildup in my forks and am now trying to replace the inner damper rod seal(s?). I have not done this before, and I have been searching and can find no information anywhere regarding the removal and replacement of these parts. Even the fork rebuild manual from Beta makes no mention of them or replacing them at any point. Where can I find instructions how to do this? I cannot easily see a way to disassemble the unit and I don't want to break something trying to do it the wrong way.
OR is it possible that this is not my issue at all? My forks get pressurized pretty quickly. After about an hour or so of riding they become noticeably stiff, and when releasing the breathers on both forks, a lot of air comes out. Would there be any causes for this other than a leaky inner cartridge? Can I tell if the cartridge seals are leaking or not without disassembling it? Could it be the main fork seals causing it even though they don't leak any oil?
Air is likely getting sucked in through the fork seals, breathers, or O-rings of the base valve or cartridge assembly at the top of the fork.
The most common cause is leaking through the fork seals when the bushes are worn.
I agree with that in full. It's worth doing bushings and seals on the outer fork tubes first.
Also, cartridge seals won't cause air to enter the fork assembly. Bad cartridge seals will allow the cartridge to lose oil, but then the forks will have a top-out feeling as they lose aerate and lose rebound damping control.
Another source of air intrusion is a leaky or dirty set of push-button fork bleeders.
Nearly EVERY set of used forks I disassemble that has push-button bleeders has rust on the springs, or moisture inside.
The OE style bleeder screws are the way to go... There are some older brass KYB screws available, they last longer than the aluminum stuff used these days.
Okay! Thank you guys for the info! I have installed new bushings and main fork seals and now have to do some testing. I had skf seals and bushings in them, and I do remember when I installed those I had a hell of a time getting the bushings in. They required a lot of pounding with the seal driver and didn't seem to fit as good as the oem ones. Hopefully those were the problem. I actually used the oem bushing/seal kit from yamaha this time. Same part number as the set for my yz250. They fit right in no problem, and seem much smoother than the skf's. Time will tell.
As for the air bleeders, yes I do have the Motion pro push button bleeders. Going back to the stock screws will be my next test if the new bushings and seals don't fix it
OEM bushings with SKF HD seals are the combo I've had the best luck with on the KYB and Showa stuff.
On WP stuff I run the OEM kit from KTM parts since they use a variant of the SKF seal.
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I found this thread because I’m also trying to change my cartridge rod seals. Unfortunately the solution was not mentioned…I have the proper 28mm holding clamp, I’ve heated the end of the tube holding the seal head, but I still can’t break it free. Any tips? Thanks
About 250°F is more than enough to soften the thread-locker. I wouldn't let it get any hotter than 300°F.
Check to see if there are dimples staked into the tube around the threads.
Yours doesn't look old enough to have the staking, but it's worth a check.
If the tube is not staked, you should be able to twist it free once it's warmed up.
Good info! How does one get this part off if it is staked? Dremel?
If you cut into the staked portion of the cylinder, I believe that would be above the o-ring on most KYB seal heads and it would leak when re-assembled. The seal head design changed over the several generations of cartridge and I don't remember how high up the o-rings were on the oldies...
I've never had to deal with a staked cartridge seal head, but I think I'd heat it up to 300°F, let it cool and introduce some WD-40, then heat it up to 200°F and risk threading it out. If the threads get wiped out, I'd replace the cartridge(s) with more recent parts.
I do everything I can to work on KYB stuff that is 2008 or later to avoid some compatibility issues.
I think you have to go back to 2005 or 2006 to get staked seal heads.
Thanks. No dimples, I just had to heat it up more. On a different note, I had a hard time getting new rebound piston seals into the bore. They have to stretch a little to install them, and didn’t contract enough to go into the cartridge very easily. Even tried the freezer!
For the wear bands, lots of guys wrap them super tight in electrical tape, then leave them in the freezer.
The stretched tape applies force pretty evenly to shrink the bands.
The way they do wear bands in production is to force them through a special sizing tool.
That tool is just a polished bushing that ensures the wear band is round and ends up within the correct diameter range.
New bands drag a little in the bore when lubricated.
That's part of the suspension "break-in" you feel as you ride a new bike and it gets less harsh.
Great info; thanks!
Late update: After replacing the skf bushings and seals with the yamaha branded oem bushings and seals, the air buildup problem seems to be mostly solved. Hardly any air buildup now even after riding for a couple hours. I suspect the tiny buildup I still get may be caused by my push button bleeders as suggested above. Trying the stock bleeder screws next
I had the same issue with a seal and bushing kit I got from InnTeck. I thought it was all SKF when I purchased it but when I received it, the bushings were branded Innteck. After several rides with air buildup, I removed the bushings and replaced with OEM from KTM and with those and the SKF seal kit there is no more air buildup.
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