KYB twin chambers
- Thread starter terry hay
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phoneman064
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- Apr 6, 2004
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terry hay said:
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.
bclapham
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- Nov 5, 2001
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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.
good to see you back, its like a mortuary in here these days.
- Thread starter
- #5
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
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
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
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
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- Thread starter
- #7
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
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
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
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
- Thread starter
- #10
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
Terry
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...
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...
bclapham
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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.
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.
Where did I go wrong?
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 :bang: :bang: :bang: :bang:
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 :bang: :bang: :bang: :bang:
marcusgunby
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- Jan 9, 2000
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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,
steve125
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- Oct 19, 2000
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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 :coocoo: ...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. :cool:
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.
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 :coocoo: ...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. :cool:
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.
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.
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....
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....
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
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
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steve125
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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.
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.
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.