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KYB twin chambers
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Posted by: terry hay---------------------

Has anyone else noticed the problems associated with bleeding the KYB twin chambers? They're not quite ready to take on the Showas just yet.
Terry Hay

Posted by: phoneman064---------------------

Quote:

Originally Posted by terry hay

Has anyone else noticed the problems associated with bleeding the KYB twin chambers? They're not quite ready to take on the Showas just yet.
Terry Hay

Seems like the racetech recommendation for 150mm is too low. ICS spring meas 1.51. The craftmanship seems not quite to Showa level. Like working on the showa better. Took 2 tries to get the air out.

Posted by: bclapham---------------------

Terry- i had heard that one of the tricks on these forks is to drill some holes in the chamber above the piston- i dont know if this is related to the bleeding issue though. i have also heard that many people get oil coming out of the top of the fork when they undo the airbleeder screw, oil comes out the top of the fork.

good to see you back, its like a mortuary in here these days.

Posted by: russ17---------------------

Most that I talk to, have the problem of getting the rod to full extension after the bleed procedure is done...(as done like the showa)
The key to this is to keep a positive charge on the rod at all times within the bleed procedure.

Russ

Posted by: terry hay---------------------

The problem that exists in the KYB TCs is related to the volume of oil being expelled from the internal chamber. Obviously the shape of the piston itself creates a pocket that traps air causing it's own havoc. KYB are clearly aware of the issues of cavitation and have taken extreme measures to control it, but have failed to address the contained oil volume oversight. The excess oil discharged is due to the limited travel of the IC piston. By placing a spacer under the IC spring, the piston is repositioned allowing further travel or displacement before exhausting any excess oil to the outer chamber. Clearly there is finally a legitimate case that warrants replacing the original IC spring with an aftermarket option. They need to be longer. Drilling the hole in the upper potion of the piston will reduce the total spring force and will make the fork more responsive to movement. I have been replacing the upper o-ring with a PTFE band which eliminates the seal but also further reduces drag. By placing a taper on the compression bolt shaft you can have the internal piston seal do the discharging rather than the external o-ring. This will efectively eliminate any trapped air. You would then require the previously mentioned hole in the upper portion of the piston to allow the discharged oil an escape path to the outer chamber. Showa have had issues in the past with their piston seal wearing the compression bolt shaft when they were made from alloy. KYB have also made the shafts from alloy. Time will tell if this was a mistake. There is a gaping hole for an aftermarket kit for this fork containing...a longer IC spring, a stainless comp bolt rod and a PTFE wear band.
Incidentally...We tested these mods with no other changes on a YZ250. The rider said the fork was clearly more stable. Any headshake was gone and the forks no longer fell through the stroke. As I mentioned previously KYB have taken extreme measures to counter cavitation. A bleed in the rebound / midvalve piston. A bleed in the rebound piston band. A clearence shim on the midvalve itself and a valve stack on the compression adjuster circuit. All valid steps to avoid cavitation but when you have a reduced oil volume or negative pressure situation, you have cavitation built in and no counter measures are going to be effective.
Terry

Posted by: russ17---------------------

Terry,
Very informative. Here's the question I have. First does the size of the piston itself limit it's travel compared to a smaller one?
You spark my interest in your comments on the negative pressure situation caused by oil being expelled from the internal cart. I went out and checked mine.( I have not checked this after spending considerable time figuring out a bleed procedure to counter the negative pressure associated with the so called normal type bleed procedure). I using a bleed procedure that works and I am happy to report no negative pressure.
Your comments about the spacer under the ICS spring, I found very interesting. The thing that comes to mind here, would be ICS spring preload .( I know depending on the thickness of the spacer.) My question is, if we are creating an ICS preload here, (which would increase the spring forces) would drilling the bleed holes above the piston offset this equally? ( Example:by my calculations the overall spring rate for the 05 YZ 250 is .524 with zero ICS preload ).
Adding 5mm of ICS pre load ,the overall rate increases to.539 which comes to a 20.23% difference.

Russ

Posted by: terry hay---------------------

Russ
The pvc is the piston.
By adding a spacer you are simply reducing the freeplay in the spring itself. Which standard is appr. 12mm. What I am trying to achieve is a lower starting point for the pvc piston. Obviously you would increase the potential spring force overall as it would now have to compress further before the bleed process occurs.
Try this...
Fill the cartridge to just above the diameter change. Pump the rod to displace any trapped air. With the oil just above the diam. change compress the rod completely and measure the height change in the oil. You will find it is appr. 35-36mm. Now if you measure the travel in the IC piston from starting position to exhaust, you will find that it is also 35-36mm. This would be fine except for one thing. The comp valve and post have to occupy some of this space. This means the oil being displaced by the rod will now raise the oil height above the original 35-36mm exceeding the travel of the IC piston. So in fact, the reason the rod fails to fully extend is due to the valve and post volume being discharged. I have seen the rods full extend with a trapped air situation. Obviously the compressed air adds to the spring force assisting the extension of the rod. When you invert the cartridge and compress the rod you can both see and hear the lack of damping at the end of the stroke.
Terry

Posted by: russ17---------------------

I saw the free play that you talk of. It was just my observation that once the IC piston entered the the cart it moved and the free play was no longer there. When moving the IC piston by hand, it seems to lock into 2 positions 1 were there is no tension on the IC spring ( the 12mm you talk of) and position 2 were there is a slight tension on the IC spring.( were it takes up the 12mm)
Upon entering the base into the cart, the IC pistion always moved to position 2 were there was tension on the IC spring. Seeing this, my thought was this was the starting point of the IC pistion movement( with the tension on the spring) and then moving from this position. Upon removal of the base( even with suction ) the IC piston was always in position 2 with no free play on IC spring. From seeing this, is were my opinion was coming from.( if the IC piston was indeed in position 2 from the get go then adding the spacer would add preload.)
thanks for the insight.

Russ

Posted by: russ17---------------------

Terry ,
I did invert the the cart and you are right on the money. there is indeed a small amout of air, enough to extend the rod.

Thanks
russ

Posted by: terry hay---------------------

It's extremely difficult to get the air out completely unless you modify the compression post. You can of course lay the cartridge on an angle appr 45 degrees. have one bleed hole uppermost and cover the other with your finger. The top o-ring seals first which will allow you to have the lower portion of the piston enter the oil, displacing most of the air prior to it sealing. This wont work however if the top of the pvc piston has been modified (drilled)
Terry

Posted by: russ17---------------------

I will get some spacers made

Russ

Posted by: aurora---------------------

very intresting your theory on the yz suspension, what size of a bleed hole and approx. where should you drill the holes. thanks

Posted by: Studboy---------------------

Maybe I'll stick to my "old school" forks... these twin chambers seem difficult!!!

Posted by: mop---------------------

Adding preload to the pressure spring helps the system retain a positive charge on the oil after bled and during use. At first, I thought maybe the blow-off holes in the free piston tank were too low, but adding preload did the same thing. Having the free piston release excess oil volume from the internal damper on the "inside" of the piston AND having communication (a couple of holes) between the pressure spring chamber and the outer "oil level chamber" is supposedly a SHOWA patent which KAYABA could not infringe upon. So the convoluted method which comes stock is a result of this. The Showa system apparently allows a substantial amount of oil to enter the internal damping chamber through the shaft oil seal during operation, and "bleed-blow-off" occurs often while in use. With the Kayaba, this is not the case so much. The oil seal on the shaft seems to seal much better. I had a Kayaba fork with some problem with excessive wear inside the damper chamber, and when I disassembled it, the outer chamber oil was clean, but the oil inside the damper system was BLACK?!?!....this leads me to assume that this chamber is truly separate from the other. I personally do not think this is an advantage, as the "circulating" feature of the Showa system constantly bleeds emulsion from the damping system.
I have had luck with bleeding the inner chamber of the Kayaba fork by filling and bleeding the cartridge and piston rod, then installing the base valve ass'y (with the pre-load increased) just deep enough to squirt oil out of the side holes. Then I put the whole cartridge in a vise at about a 60 degree angle with the hole in the cartridge tank up. I push against the base valve while compressing the piston rod slowly.
There will be a "farting" sound as the air trapped beneath the free piston cavity escapes because of the angle the cartridge is at. I slowly stroke the piston rod up and down a few times until I compress it to a little before full stroke. Then I extend the rod and screw in the base valve. When done properly, this is the best way I've found to bleed the air out and have a fully extended rod after bleeding it and charging the rod full stroke...

Posted by: bclapham---------------------

thanks for the info Mop and Terry.

i was always under the impression that the showas were actually a separate system, but after talking to a friend, i discovered it is constantly circulating- i thought i had bad cartridge seals when running different oils in the inner and outer chamber- one oil was red, but both fluids came out red a few weeks later!!! i now run the same oil in both chambers, its good since we can make simple valving changes at the track and keep oil levels etc essentially the same.

my friend has done limited work with the new KYB twin chambers on the 05 250- his words are they are a 'biiiatch" to bleed and not ready to take on the showas just yet.

One word of caution about these KX forks- he made midvalve modifications and the nut that holds on the end of the rebound stack is very shallow and difficult to take off and still keep a few threads to put them back together.

Posted by: russ17---------------------

Mop.

Good to have you on board.

Russ

Posted by: J.Gordon---------------------

Allright yesterday I replaced my seals and oil on 05 yz250. The basevalve seemed to bleed out ok. Today I was trying it out on the track had some hard landings the seals started seeping. I put it on the stand and the forks were loose, game over. Take the bike home pissed off with my 10 laps. Anyhow pull the forks apart and the locknut and damper adjuster are stripped out and seperated. When installing this assembly I maintained there spec of .02 - .04 gap between the two. But now there alot of little pieces tore up. Now heres the strange thing I had a reputable tuner revalve for cross country racing. When pulling the forks apart I found two large washers between the fork spring and the nylon spacer on the bottom. Well those little home depot washers are tacoed but in my opinion don't belong there anyhow. Three things that factor in my woes. First off was it just me putting it back together wrong some how. Second, It was set soft for woods riding and not mx, could it been the hard landings. Or was it those damm washers . Has anybody had Enzo work on there forks ? Parts only estimate at 900.00 .Sorry about being longwinded I just had to vent to peeps that might understand.

Peace

Posted by: marcusgunby---------------------

The washers are preload spacers as the new kybs come with no preload, he did the right thing IMO installing them, if you make a fork too soft it will just bottom-no damage will occur, so it looks like it was a installation problem,

Posted by: steve125---------------------

J Gordon

This 1mm gap between the locknut and the rebound adjuster is measured before you tighten the adjuster up against the locknut. You may have left the nut loose??

Another note: on my forks both bikes, the 125 and 250 really dive in the mid-stroke. I ended up with the compression adjuster at 5 out and it got harsh.

So I decided its time to up the spring rate 1 step. In doing so I drained both fork outers over nite to see where the oil volume was at from the factory.

I was suprised that all I could drain from both forks was 225cc

...and I had already added 10cc prior to draining at the track....the factory spec is 245cc, If I would have known this I may have not needed to go up 1 rate with the springs?

It's no big deal really since I only purchased 1 .46 spring for the 250, that with the std .44 spring equaled out to an overall rate of .45. And the std .44 250 spring(removed), will go in the 125 along with it's std .42 to end up with a total rate of .43. For my weight, it puts me right on the money with just the purchase of 1 spring.

I set my oil levels at 240cc with the stiffer spring rates, and will put the clickers back in the middle ranges and then re-test.

Posted by: J.Gordon---------------------

Thanks for the advice guys. Steve now this maybe where I went wrong. The only way I was able to achieve the tolerence was back off the lock nut and basically bottom out the damper adjuster and bring the locknut up to the adjuster. Otherwise the damper adjuster would spin on when I put the assembly together. Was the adjuster supposed to be finger tight. Damm it I hate learnin the hard way. All I wanted to do was change the seals and oil.

Posted by: steve125---------------------

J. Gordon

The adjuster to locknut torque is 21ft. lbs.

Well at least now you know what happened, sorry to hear that, it happens to the best of us.

Posted by: mop---------------------

J.Gordon:
Did the forks work okay BEFORE you changed the seals? It sounds like the "washers" you found between the plastic spacer and spring do not belong there. Preload to the new KYB fork must be put between the cartridge "ledge" and the upper ALUMINUM spacer. If they are put at the bottom of the spring, the oil lock ring can clip it and "taco" them if they hit. I do not see how this could strip out the locknut though? When tightening the lower fork locknut and fork "cap", you should first turn the rebound adjustment to full soft (counterclockwise all the way) then bottom it out before tightening the lock nut. Sometimes if it is adjusted too tightly, when you "bottom-out" the cap, it will be too high. But as I said, I don't think this would allow it to strip out....

Posted by: J.Gordon---------------------

Yes Mop the forks worked before primarily crosscrountry racing. That was the first time on a track. The steel washers I.D. was to small to fit in between the ledge and the aluminum spacer but thats where I thought they should of been. Mop the locknut was not stripped out. It was the damper assembly rod and the damper adjuster that stripped from one another. Heres where I'm still grey I did every thing you said but when bringing the locknut back up to the adjuster I put
a filler gage to obtain the tolerance. With the gap in place I don't understand how that can be a locknut. What do you mean by the cap being to high? I went to the local dealer to price out the damage. The parts manager said another guy had the same problem after changin his own seals week earlier. I guess I'm not the only knuclehead I wish I could compare notes with him. Also the dealer would not sell me the individual parts that I need [BS} just whole asemblies to make matters worse. Anyhow I hope I can get these forks done by this next weekends Wild Boar Enduro. This bike has been a thrill on and off the track. First a Smoked clutch, splitting case is always fun on a new bike and now this. But when shes on shes on I'm not givin up on her yet. I hope I didn't hijack this post. But it might save someone from goofin up.

Thanks again for all the therapy

Posted by: steve125---------------------

Gordon

I think this gap between the rebound adjuster and the locknut is where you are confused. The reason the manual even states a needed gap is to make sure the rebound adjuster is threaded all the way up on the damping rod before the locknut to rebound adjuster is "tightened" 21 foot lbs. Thats it, the gap does not remain open in any fashion upon final assembly. The locknut must be tightened to the adjuster. This secures the damping rod to the adjuster in the proper position.

This is why your rod end and rebound adjuster are now stripped, because they were never secured. As the forks were moving up and down, the rod was slowly unscrewing and the threads were damaged in the process.

Posted by: J.Gordon---------------------

Allright Steve I see the light now. The manual mislead my peabrain. I never felt comfortable with that part of the procedure like I knew something didn't feel right. I keep on reading the part " Out of specification > Retighten and readjust the locknut" was screwing with my head. The whole gap thing still is still a little foggy. Originally I had rebound setting all the way out. Then I screwed the adjuster until it bottom out and brought the locknut back up to adjuster and snugged her down. I think I would have been better off than I am now. Steve without a doubt thats where my trouble originated from. Thanks I can now sleep tonight.

Posted by: mop---------------------

J.Gordon:
The steel washers you are talking about have no business being in your fork in the position you are talking about. If the inside diameter is too small to fit between the ledge and the aluminum spacer, then FOR SURE they are too small for the oil lock ring to fit between! Get back in contact with the company that originally put those in, and question them. As I said, they wouldn't cause the problem with stripping the rod, but that is still not correct. Call around to different suspension shops to ask if these parts can be bought separately. Good luck.

Posted by: bclapham---------------------

Gordon, check out http://www.enzoracing.com enzo is supposed to be the main man for KYB stuff and since he sells a lot of genuine parts, maybe a good source for getting hold of the parts you need.

Posted by: marcusgunby---------------------

sorry mop is right and im wrong-you have to put the spacers in the right place.

Posted by: J.Gordon---------------------

In the midst of the monday madness I was able to next day air the forks down to ENZO for a small fortune. Talked to fella by the name of Ross he knew exactly what page I was on. Ross was patient and very informative [sold]. It looks like I might make to the races after all. I didn't say that outloud did I. It never fells it always seems like a race to the race.

Posted by: James---------------------

Sorry to revive this old thread.

I wonder if there was any better solution at this point or if teh spacer and bleed hole are the best fix. I understand the concept behind the ICS spacer as the damper rod volume seems to be missing from the piston travel equation. Where I am stuck is the part where you drill the hole in the piston. I can see where that would allow the trapped air to escape, but won't that allow air back in?

Also, is it best to leave the bleed shim in the mid-valve or would removing it and setting up the mid-valve more like a Showa with a full diameter shim against the valve get me closer to the Showa feel??

Posted by: bedell99---------------------

I was thinking about sending my forks over the winter, but I will probably wait. I have a feeling yamaha will make replacment ICS springs and that will be my ticket. I'm really surprised one of the suspension companies don't sell a do it yourself kit with the 7mm spaces, an ICS spring and a diagram for bleed holes.

Erik

Posted by: russ17---------------------

My personal opinion on the air/oil separation that KYB came out with, was not to make it like the showa were as on the showa the air spring has a major effect on the floating piston. All though the KYB type missed the boat a bit on the piston position, and shape YZ (allowing it to bleed off to soon) I think it has its merrits when fixed correctly.
I personally like the feel of the KYB over the Showa, But I ride GNCC type stuff
I guess we will see what they have done on the 06.

Russ

Posted by: James---------------------

Even if they didn't intend to be like Showa, that's what I would prefer. I'd gladly bolt some of my CR forks on the YZF (if it were possible), Eboy the KYBs, and be done with it.

I think Showa TC forks are the best for me when it comes to jumping anything bigger than 20 feet and riding at speed. I just don't have confidence in the 05 Yamaha/KYB forks yet - TOO squishy. Sucks to buy a new bike and have it basically sit for 5 months while sorting out fork issues.

Posted by: russ17---------------------

As I stated James this was my personal opinion with the modifications. And you are correct in your statement without the modifications. This was just my opinion. I like the feel of the KYB T/C

Posted by: James---------------------

Quote:

Originally Posted by russ17

As I stated James this was my personal opinion with the modifications. And you are correct in your statement without the modifications. This was just my opinion. I like the feel of the KYB T/C

I understood you were just expressing your opinion, and I was just further clarifying my wishes for purposes of conversation, definitely not arguing.

Restated, my comment could read: I would gladly take Showa performance over the current unmodified KYBs and be happy.

When I get modifications done, I'll give them a fair shake and I may like them better too

What is it they say....the best you know is what you have ridden or something like that???

Posted by: bedell99---------------------

I like the forks, they where real firm when I got the bike, but softened up a lot. The best thing I did for the pushing was throw a 756RR tire in the front. I think the rebound is a bit fast and i get headshake on slap down landing sometimes, but other than that i think the compression is good.

Erik

Posted by: James---------------------

Mine were the same Erik. I think the softening has to do with the excess bleed and the fast rebound has to do with the bleed shim on the mid-valve. Once they got soft, I had no trouble with pushing because the nose would drop 6-8 inches going into the curves.

Posted by: APBT---------------------

Erik,
I've had relatively good luck with a 756RR up front, the forks raised 5mm in the triple clamps (to the line), and rebound at about 7-9 clicks out from full firm.

YMMV

Posted by: Dan105---------------------

OK, when I had my Honda with TC showas for the last few years I had it down pretty good working on the forks. I could do everything to them and even came up with my own valve stack. I was very very happy with the forks and I enjoyed working on them. After reading this entire post I'm afraid to dig into the KYB on my 05 YZ. Even more soo I dont know who to send the forks out to if im not going to work on them myself. I need them revalved for cross country racing. I want the mods done that TerryMay was talking about. Any suggestion on who to send the forks to for offroad mods and also someone that knows what mods to do to correct the forks?

Dan1052002@yahoo.com

Posted by: anca---------------------

it came the time to change the oil in the fork for my 05 YZ250F and i want to make also the changes i have read here(also in thumpertalk).But it is not very clear where to instal the spacer in the IC, on the piston side or the upper side, also it must be 6,7 or 8mm? The spacer for the main spring i understand that it must be in the upper part of the spring, 4,6 or 7 mm?
If i use the bleeding method described by MOP, do i still have to drill the hole in the piston and make a chamfer in the shaft?
If yes, what this chamfer must look like?
Thank you

Posted by: terry hay---------------------

The spacer required should be 8mm in length and installed between the cap and the IC spring. The bleed on the rod should be placed 54.5 mm from the valve end of the shaft. Personally I prefer to use a taper rather than a hole. This is kinder to the seal and will ensure longevity. You are mistaken if you believe the rebound to be too quick. The free bleed on the rebound / midvalve piston will create this impression if you simply push on the forks. At riding speed however the forks are in fact over damped and fail to respond adequately to impacts. Removing the clearance shim from the midvalve will stop the forks from diving so readily under brakes which will in turn also assist the rebound. Naturally rebound is reactive to compression so therefore if you prevent the fork from compressing so easily you also reduce the rebound effect.
I can't help but feel that KYB were aware of the cavitation issues with this fork as there were too many attempts to overcome the problem. The rebound bleed, piston band bleed, midvalve clearance shim, adjuster circuit shimstack. All of these inclusions will promote oil flow to the rear of the midvalve piston as a priority to assist with cavitation. But none of this will count for anything whilst the lack of oil volume continually provides a low pressure area inside the cartridge. Foaming of the oil and a lack of damping will always ensue. Good luck with your mods. Hope I have helped.
Terry Hay

Posted by: lemons r yellow---------------------

very informative Terry.
Thank you
Where do you drill the 4mm hole in the piston?

Posted by: bedell99---------------------

I fthought that fork is underdamped on the compression side and that is why it is diving. This winter I'm sending them out. The more i ride and the more it breaks in the fork keeps getting softer and softer. I only weigh 155 and the fork bottoms and dives. it actually is not that bad, but not as good as the showa. the only thing its has stoped doing as it has broken in is the heashake has stopped.

Erik

Posted by: James---------------------

Quote:

Originally Posted by bclapham

i was always under the impression that the showas were actually a separate system, but after talking to a friend, i discovered it is constantly circulating- i thought i had bad cartridge seals when running different oils in the inner and outer chamber- one oil was red, but both fluids came out red a few weeks later!!! i now run the same oil in both chambers, its good since we can make simple valving changes at the track and keep oil levels etc essentially the same.

I wanted to explore this a bit further since we all seem to be trying to accomplish full extension of the dampers on the KYB.

If the system is constantly circulating (to be clear - I am not disputing that it does) then why do none of my Showa dampers ever FULLY extend on their own; either after I have bled them or after they have been used in the bike for a few hours? I have even left the inner chamber overfilled (so that the rod fully extends with authority), used the forks, removed the damper, and it will still stop .5-1 inch from full extension. If the system was designed to circulate, then the cartridges should self-bleed/self correct with use right? Is this .5-1 inch short of full extension normal? My guess is yes.

To get to the root of my question....if this is normal for Showas, why would we expect the KYBs to fully extend after bleeding?

Posted by: brentl---------------------

I'm swapping my 05 YZ250 to my dealer for an 06

Was going to get 05 reworked but am guessing that 06 fork is improved.......Do any of you guys know if the 06 is significantly better ?

Seems that the front doesn't bite and skids, even with a 756RR ( I'm coming off an RM tho )

Your thoughts and comments are appreciated

Posted by: bedell99---------------------

Actually the bike grips very well with that 756RR tire in the front. The problem I'm having is it is softning up. The fork itself its not bad. I don't have much headshake anymore and the rebound seems to be pretty good unless its the forks hits many successive hard square edge bumps in a row. That is my biggest complaint. Like i said in my previous post I'm going to send the forks and shock out this late fall/early winter.

Erik

Posted by: brentl---------------------

Any comments on my question about the 06 "speed sensitive" forks...Think they might help with the front end pushing?
I've raised my tubes 12mm btw

Thanks for any info!!!

Posted by: frankrock363---------------------

Quote:

Originally Posted by brentl

Any comments on my question about the 06 "speed sensitive" forks...Think they might help with the front end pushing?
I've raised my tubes 12mm btw

Thanks for any info!!!

Just curious what do you have your sag set at?

Posted by: brentl---------------------

Around 100 now but have tested from 90 to 110 mm

Posted by: russ17---------------------

Brentl,
I feel the pushing that you described will have nothing to do with the new SSS fork design. The 05 fork IMO was a factor of other issues associated with the stock 05 forks as mentioned in this thread. Once the issues with the 05 fork were addressed the fork worked good.
I am sure Ross M. has made the KYB folks aware of these issues. I have yet to see the 06 forks so I really don't no and this is just speculation on my part.

Posted by: fnengineer---------------------

Terry,

I am going to be servicing a set of 05 forks and I was hoping I could bug you for a bit. Possibly looking for an upgrade kit like you described earlier. My email is mx174@hotmail.com

thanks

Mike

Posted by: bedell99---------------------

Now that this thread is back, I have a question is anybody making aftermarket ICS springs that are longer. I would think that would be a hot seller.

Erik

Posted by: James---------------------

Quote:

Originally Posted by lemons r yellow

very informative Terry.
Thank you
Where do you drill the 4mm hole in the piston?

I have read this thread 8 times and I still don't see a clear answer on this.

I understand the taper on the base-valve post part of this fix. Is there an additional hole that needs to be drilled in the PVC piston? Should it be on the side of the piston with the intention of creating a path to the outer chamber?

Posted by: Zenith---------------------

Sorry to revive this old thread, but I have a quick question before I rebuild my 05 YZ125 forks if somebody could help me out.

I've put an 8mm spacer above the ICS spring and bled the cartridge (125mm oil level and bleed at 45 degree angle as mop suggested), the rod extends all the way out now so all seems good. I didn't drill/taper the adjuster post as the cartridge seemed to bleed OK without it.

My question is on the main spring spacer though. What size is good here? I believe the springs are negatively preloaded 5mm stock. I've put a 9mm spacer (so effectively 4mm preload on the spring) in to one of the forks and rebuilt it, but not being familiar with fork preload I thought I should check if 4mm was OK before going on with the second fork and going riding tomorrow. I feel I could do with a bit of extra preload anyway as I'm on the heavy side of the recommended weight for these springs. But not knowing what sort of preload figures are "normal" I don't know if 4mm is WAY to much, not enough or perfect.
Even if somebody could tell me some typical preload numbers I'd know if I'm way off or not...

Thanks for any thoughts!

Posted by: marcusgunby---------------------

Philip its hard to say whats the right amount of preload, i think some showas come with as little as 3mm and others more like 10mm(the 05 crf i think has alot of preload) i would start at something like 4mm as its got bto be better than -5mm.

Posted by: steve125---------------------

Phillip, I set mine at + 3mm and it works real well. If you go to far it may effect your turning. I think thats why Yamaha set it negative in the first place.

Posted by: Zenith---------------------

Went with 4mm as this was the size of my spacer (which was an outer race of a CR125 wheel bearing LOL).
I'm not the best at noticing changes in suspension, but I rode today and the forks seemed much improved, none of the unusual 'effects' I was having when riding before. Not sure what made the main difference but for the record I went with 8mm spacer on the ICS, bleed hole not drilled, bled as per mop's instructions (got full rod extension this way, cheers mop!), 9mm spacer on the main spring, 245ml oil level. I put in a set of Synergy seals as well, should be interesting to see how they go. Bit of a pain to install, but once I'd done one it was easier.

Anybody know if similar things apply to the 06 version of these forks, specifically the ones on the YZ125?

Posted by: Zenith---------------------

Nobody knows if the 06 is similar or does nobody care anymore?

Posted by: yam 3---------------------

i think the 06's are "new and improved"

Posted by: anca---------------------

When I rebuilt the forks ( ‘05 YZ250F ), I installed the spacer in ICS, bleeding as mop advised ( full rod extension like Zenith ), no piston drilling or rod modification, no spacers for the main spring. The result was a more predictable front, better cornering, but still pushing, and it became harsh. I checked the fork travel and it seems that it’s not using the last 20mm. I tried all the clicker combination, even with the air bleeding screws out. Still 20mm not used, with the screws out it became more plush but still it’s not like it was before.
The oil is Ohlins, 245ml, 5wt in the ICS (couldn’t get Kayaba). Now I understand that Ohlins has a 2wt oil, especially formulated for ICS.

My problem appeared because of a to tick oil, or because I didn’t done the drilling and the chamfer on the rod?

Please help, I rode a 525EXC today and it’s cornering better than my YZF !!!!

Posted by: anca---------------------

Hi Zenith, does you fork became harsh after modifying it? I see you are online

Posted by: Zenith---------------------

No I didn't notice them being harsh, I just thought all round the modifications hugely improved the handling of the front end. I'm using almost all the fork travel, though I'm about 200lbs with gear.

My supposedly un-leakable Synergy seals are now leaking by the way. 3 months doesn't seem that good to me from a set of seals, at least not at that price! I could buy 4 sets of ordinary ones for the money, that would have got me through at least 2 seasons...

Posted by: James---------------------

If you take the forks apart and clean the seals as opposed to replacing them each time they leak, they may last two seasons or more. It's usually dirt in the seal, not a tear. They definitely don't wear out in three months. I haven't replaced a seal of my own in 4 years.

I feel like my YZF forks got harsher after the mods but that may be for two reasons:

1. Before the mods, I was most likely running low on fluid in short order.

2. I rearranged the mid-valve to get rid of the bleed on teh compression. This may have also affected the rebound as the fluid now has to pass 100% through that circuit.

#1 may be the difference you are feeling. What do you weigh?

Posted by: anca---------------------

I’m 180 lbs without gear.
Today I extracted from each fork 30ml oil and it helped some with harshness, but the fork is still blocking at 20mm from bottom. So it’s not from oil level, I guess it must be from ICS, I’ll experiment further.
I don’t know if I have to drill the piston and chamfer the rod ( the ICS is well bleed by mop method), I’m afraid to do it because it is a permanent modify.

Posted by: James---------------------

I can't imagine what would be restricting the travel unless you put it back together wrong. Did you get all of the spring washers/bushings back in the right place? There is an upper and lower one that go on the outside of the damper assembly with the fork spring. Also, where did you put the 9mm spacer?

Posted by: russ17---------------------

Guy's, I would look at the TCV ( Transfer control valve) This is position sensitive. Great for anti bottoming.

Russ

Posted by: anca---------------------

As far as I remember everything is put together correctly as is sown in the expanded view in the book. The ICS spacer is 8mm and is installed on top.
Anyway I will disassemble the fork, I’m very unsatisfied with the new turning habits of my bike, I feel like the fork is not diving enough in turns.
If you have any idea of what could be wrong please let me know, I don’t want to do the same mistake second time.

Posted by: dishman---------------------

i have a 2005 250f. i need to know the proper amount of oil

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