Yamaha 06 SSS Fork Cardtridge oil problem

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Sep 13, 2007
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#1
I replaced the oil in the cartridge with yamaha S1 oil and put ATF in the outer chamber. After riding 20-30 miles, the forks became much harsher and stiffer.

When I got home I pulled the cartridge off and ran it through it's full stroke and red oil bled out of the over-flow holes. The S1 oil is originally clear and I don't see how the ATF oil got sucked inside there?? What do I need to look for and what can make this happen?? I can only think that it was somehow sucked into the overflow holes to the inside, or the seal at the bottom of the cartridge that seals against the rod, but that seems unlikely that the seal would go bad in both forks at the same time.

Is there any possibility this is a bleeding error?? I don't really think that it is as I know how to bleed these cartridges now, but any help or possible solutions would be greatly appreciated.

Thanks in advance.
 

mop

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#2
YROC:
The reason that there was ATF in your cartridge is because the oil inside the damping cartridge and the oil in the air spring chamber will mix by design. When the fork bottoms out, the "head" of the cartridge has the "oil lock ring" attached to it and it goes into the "oil lock case" at the bottom of the fork. When the cartridge head enters the oil lock case, the "bottoming cone" feeling is a strong hydraulic cushion created by the oil lock ring entering the oil lock case, displacing oil up around it. Think of it like forcing your fist into a mug of beer: the beer will be forced out of the mug around your fist. The hydraulic resistance is the beer forcing it's way around your fist as it displaces area in the mug. This situation creates a very high pressure inside the oil lock case as the oil is being forced around the outside of the oil lock ring. THis high pressure actually will force oil INTO the cartridge past the oil seal and cartridge rod. The oil seal on the cartridge rod is directional: it keeps oil INSIDE the cartridge, but does not really keep oil from being forced IN by pressure. Everytime oil is forced INTO the cartridge, the floating piston position becomes higher, but as the fork is bottomed, it also purges oil out of the top like it does when you are bleeding the assembled cartridge. So oil "circulates" in and out of the cartridge with the oil outside of it. That is why your ATF made it's way into the cartridge (and S1 made it's way OUT of the cartridge). By the way, this same function occurs with SHOWA twin chamber forks.
I have a question for you, why did you use ATF in the outer chamber (OR in the inner chamber for that matter)? S1 oil is designed to provide consistant damping force in a slightly pressurized environment (inside the cartridge) and also provide high film strength lubricity for the structure parts (inner and outer tube bushings). I don't think ATF offers any advantages to either of those functions. I actually tried building a twin chamber fork a long time ago by putting two seals in the cartridge (one lip faced up and another faced down to keep oil from getting IN or OUT), then ran a high viscosity index SHOCK fluid in the cartridge forthe damping, then a thicker, higher film strength lubricity oil in the outer chamber for better smoothness. My thinking was that the shock oil would fade less inside the cartridge (not that there was a fade problem, but I thought I was being smart!) and then run a more lubricating oil where all the big friction parts were working. The project was a failure for a few reasons, but ultimately, I decided that I should not try to improve on a system that was working pretty good already and spend time thinking about things that were NOT working so smoothly....
 
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#3
The oils are going to mix slightly due to the oil film left on the parts thats it's lubricating. I would bet that most of the oil stayed put but a little contamination between the two is suspect from the nature the fork is being put through.

Also you said that red oil bled out of the overflow holes. What do you mean? Was there built up pressure inside the cartridge or are you just saying as you compressed the rod into the cartridge that red oil came out of the bleed holes? Red oil or atf should have come out of the holes because that it is a part of the outer chamber.

The harshness is not due to any ATF fluid leaking into the inner chamber if thats what your thinking. It is more likely due to poor bleeding or something of that nature. Atf has a sightly higher oil wt. and that would be a performance gain if anything.
 
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#4
mop said:
YROC:
The reason that there was ATF in your cartridge is because the oil inside the damping cartridge and the oil in the air spring chamber will mix by design. When the fork bottoms out, the "head" of the cartridge has the "oil lock ring" attached to it and it goes into the "oil lock case" at the bottom of the fork. When the cartridge head enters the oil lock case, the "bottoming cone" feeling is a strong hydraulic cushion created by the oil lock ring entering the oil lock case, displacing oil up around it. Think of it like forcing your fist into a mug of beer: the beer will be forced out of the mug around your fist. The hydraulic resistance is the beer forcing it's way around your fist as it displaces area in the mug. This situation creates a very high pressure inside the oil lock case as the oil is being forced around the outside of the oil lock ring. THis high pressure actually will force oil INTO the cartridge past the oil seal and cartridge rod. The oil seal on the cartridge rod is directional: it keeps oil INSIDE the cartridge, but does not really keep oil from being forced IN by pressure. Everytime oil is forced INTO the cartridge, the floating piston position becomes higher, but as the fork is bottomed, it also purges oil out of the top like it does when you are bleeding the assembled cartridge. So oil "circulates" in and out of the cartridge with the oil outside of it. That is why your ATF made it's way into the cartridge (and S1 made it's way OUT of the cartridge). By the way, this same function occurs with SHOWA twin chamber forks.
I have a question for you, why did you use ATF in the outer chamber (OR in the inner chamber for that matter)? S1 oil is designed to provide consistant damping force in a slightly pressurized environment (inside the cartridge) and also provide high film strength lubricity for the structure parts (inner and outer tube bushings). I don't think ATF offers any advantages to either of those functions. I actually tried building a twin chamber fork a long time ago by putting two seals in the cartridge (one lip faced up and another faced down to keep oil from getting IN or OUT), then ran a high viscosity index SHOCK fluid in the cartridge forthe damping, then a thicker, higher film strength lubricity oil in the outer chamber for better smoothness. My thinking was that the shock oil would fade less inside the cartridge (not that there was a fade problem, but I thought I was being smart!) and then run a more lubricating oil where all the big friction parts were working. The project was a failure for a few reasons, but ultimately, I decided that I should not try to improve on a system that was working pretty good already and spend time thinking about things that were NOT working so smoothly....
Mop,
Out of my own curiousity, I have a question in regards to your above post.
Is it possible that the emmulsified oil from the outer chamber could make its way into the inner cartridge, by way as you have stated..... thus allowing air into the inner cart?

After some thought, with the type of stike you are describing in order for this chamber oil exchange .The outer fork chamber would be under pressure at that time, and there for know emulasified oil?

Thanks Russ
 
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mop

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#5
Russ:
I'm not sure I understood your post......If oil at the bottom of the fork, in the oil lock case was emulsified (air and oil mixed), then it could be forced into the cartridge when the fork bottomed, but that is not really likely. The pressure in the cartridge is usually higher than the pressure in the outer chamber because of the volume. SOmetimes when disassembled, there is a vaccuum inside the cartridge, and the shaft is sucked in. THis is usually caused by the inner floating piston seal failure. If a large amount of oil leaks past this seal into the pressure spring chamber, sometimes the plastic floating piston will shatter from too much inside pressure. An easy fix to prevent this from ever happening is to drill a hole in the middle of the floating piston so that the inner and outer chambers will be equal. KYB did not do this stock because it is a SHOWA patent to have common pressure in both chambers. This mod will prevent the floating piston from shattering, but it will not prevent the inner floating piston seal from leaking....I have no idea why this happens....
 
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#6
mop said:
Russ:
I'm not sure I understood your post......If oil at the bottom of the fork, in the oil lock case was emulsified (air and oil mixed), then it could be forced into the cartridge when the fork bottomed, but that is not really likely. The pressure in the cartridge is usually higher than the pressure in the outer chamber because of the volume. SOmetimes when disassembled, there is a vaccuum inside the cartridge, and the shaft is sucked in. THis is usually caused by the inner floating piston seal failure. If a large amount of oil leaks past this seal into the pressure spring chamber, sometimes the plastic floating piston will shatter from too much inside pressure. An easy fix to prevent this from ever happening is to drill a hole in the middle of the floating piston so that the inner and outer chambers will be equal. KYB did not do this stock because it is a SHOWA patent to have common pressure in both chambers. This mod will prevent the floating piston from shattering, but it will not prevent the inner floating piston seal from leaking....I have no idea why this happens....
Thanks Mop
You read into my question just fine. My reason for this question was do to the number of the Kyb forks I have seen with very little time on them with a massive amount of air in the carts. So when I read your post, "the reason for the oil mixing issue". It just poped in my mind that " what if " there was a emulsified fluid entering by the way you suggested. And if possible a contributing factor to what we have been seeing with air in the carts, other than poor bleeding issues.
So thanks again.