New fork oil/seals...now stiffer front suspension?


32 replies to this topic
  • Justin89

Posted September 22, 2008 - 05:09 PM

#1

Hey guys, I just got my fork seals replaced today on my 2006 yz450f. Now the front forks seem stiffer...? Is it because the new oil? I havent had to change my fork seals since I had my bike so I dont know if this is normal or not? Any advice would be greatly appreciated...thanks!:excuseme: :lol:

PS. The guy that replaced adjusted the clickers on my forks as well..he said he made them softer. They were ten clicks out (or is it in?) now they are 5 clicks out. So shouldnt the forks be softer now?:excuseme:

  • MAD_POTTER

Posted September 22, 2008 - 05:12 PM

#2

5 clicks out is a lot stiffer than 10. Go back to 10 clicks out and try again. Remember, in all the way is full stiff, out all the way is full soft.:excuseme:

  • grayracer513

Posted September 22, 2008 - 05:54 PM

#3

Something that is critical in the twin chamber KYB fork is the oil level in the outer chamber. A change of as little as 5cc per side can have a noticeable effect on the perceived harshness or plushness of the fork, as well as on bottoming. If the gentleman who did your forks was not careful to fill them that critically, that could be where the trouble is. First, though, try backing the adjusters out to the base setting of ten on the compression, and see what that does.

  • Justin89

Posted September 22, 2008 - 06:56 PM

#4

Something that is critical in the twin chamber KYB fork is the oil level in the outer chamber. A change of as little as 5cc per side can have a noticeable effect on the perceived harshness or plushness of the fork, as well as on bottoming. If the gentleman who did your forks was not careful to fill them that critically, that could be where the trouble is. First, though, try backing the adjusters out to the base setting of ten on the compression, and see what that does.


Okay thanks for the tips guys:worthy: I havent actually ridden on a track with it yet but I could tell as soon as I took the bike off of the stand. Also, my suspension was sent to Enzo Racing for the revalve but I had a local suspension shop do the fork seal work...

  • trailsweep

Posted September 23, 2008 - 06:24 AM

#5

Another thing to check if you haven't is to make sure when your putting your front wheel on not to cause a binding in your forks when the suspension compresses ...cause by not centering the forks on the axle when tightening the pinch bolts...good luck

  • llamaface

Posted September 23, 2008 - 07:47 AM

#6

Did you use the exact same oil as was in there before? I discovered recently (the hard way) that the mfr's designation of the fork oil weight is not really meaningful. one mfrs 5w may be the same as someone else's 7w or 2.5w.

this chart http://www.peterverd...om/lowspeed.htm has some data that compares most common suspension oil brands.

I had used motorex 5w since the maxima 5w my tuner used wasn't available locally. I wasn't happy at all with it, and finally discovered that motorex 5w is around 50% stiffer than maxima, so I used motorex 2.5w (very similar viscosity to the maxima 5w) and I'm now totally happy again.

  • Justin89

Posted September 23, 2008 - 07:54 AM

#7

Did you use the exact same oil as was in there before? I discovered recently (the hard way) that the mfr's designation of the fork oil weight is not really meaningful. one mfrs 5w may be the same as someone else's 7w or 2.5w.

this chart http://www.peterverd...om/lowspeed.htm has some data that compares most common suspension oil brands.

I had used motorex 5w since the maxima 5w my tuner used wasn't available locally. I wasn't happy at all with it, and finally discovered that motorex 5w is around 50% stiffer than maxima, so I used motorex 2.5w (very similar viscosity to the maxima 5w) and I'm now totally happy again.


Ya I'm not sure what forkoil he used. I took the whole bike into him so idk. I'm going back to the shop today to see what's going on here...I'll come back and post what i found.

  • grayracer513

Posted September 23, 2008 - 08:33 AM

#8

The viscosity of fork oil does not significantly modify the damping characteristics of high end modern forks (all MX and high end OR bike of the last 10 years almost universally included).

This is because the valving assemblies that control damping act as pressure regulators, maintaining a designed pressure differential between one side of the moving piston and the other. This is different than the very much older approach of flowing oil through fixed orifices, in which case, thicker or thinner fluid would alter the effect.

As the piston moves through the oil, the valving opens a certain controlled amount in response to the pressure on the advancing side. If the pressure is higher, the valve will open farther in response. This is done deliberately to negate the effect of viscosity changes caused by temperature changes during operation. The fact is that a cold 5wt (with a decent viscosity index) is almost twice as viscous as a fully warmed up 15wt, and the range of viscosity change that a good fork oil will likely go through is generally about the same as the difference between a 5wt and a 20wt.

Most modern forks are designed to use lighter oils of less than SAE 10wt. If one was to put a 15 or 20 in a fork designed for a 5wt, you probably would notice some differences, but not much at all in changing from 2.5 to 5, or 5 to 7.

What a heavier oil will change is the anything that operates through fixed orificing, such as the hydraulic bottoming brakes. These usually take the form of cones or a series of holes that get progressively closed off. Since they do not operate as pressure regulators, a heavier oil in the outer camber of a twin chamber fork is a good approach to reducing bottoming.

A heavier fluid can also have a greater tendency toward cavitation at high speeds, which can cause foaming, fluid shear, and degradation of performance. But ordinarily, within a reasonable range, the fluid viscosity will not effect the general feel of the fork more than one or two clicks worth.

  • llamaface

Posted September 23, 2008 - 08:37 AM

#9

The viscosity of fork oil does not significantly modify the damping characteristics of high end modern forks (all MX and high end OR bike of the last 10 years almost universally included).


Umm. my experience, riding the forks back to back in the same conditions is completely different from your theory. Also numerous professional suspension guys have opinions that are different from your theory.

Also the link I posted, complete with charts and testing info, seems to dispute your claim. I would challenge anyone to try to fluids that actually differ significantly in viscosity in their forks back to back, and tell me they can't feel a difference.

I allow the possibility that there is some magical difference in the structure of kayaba TC forks that makes them different from WP open-cartridge forks, but the difference in fork action between motorex 5w vs motorex 2.5w (or maxima 5w) is profound, mostly noticeable in low-speed bump compliance, like you would find in idaho mountain trailriding (rocks, roots, etc...). 7-10 clicks softer on the forks with the heavier oil still left them reacting harshly to rocks and roots.

I suspect there may be a reason that suspension tuners often recommend a particular brand and weight of oil.

  • grayracer513

Posted September 23, 2008 - 08:46 AM

#10

Also numerous professional suspension guys have opinions that are different from your theory.

There are a considerable number of them, some from whom I learned this "theory", that agree with it.

Simply ask your self how much differently your fork acts between the the first 5 minutes of operation and the end of the day, during which time the fluid will have undergone a 3 or 4:1 reduction in viscosity.

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  • llamaface

Posted September 23, 2008 - 08:55 AM

#11

There are a considerable number of them, some from whom I learned this "theory", that agree with it.

Simply ask your self how much differently your fork acts between the the first 5 minutes of operation and the end of the day, during which time the fluid will have undergone a 3 or 4:1 reduction in viscosity.


Well, according to the link i posted, that varies a bit depending on the characteristics of the particular fluid. Apparently some change viscosity more than others with temperature. I'm not even sure what a 4:1 reduction in viscosity would actually entail, much less whether that is a realistic figure for modern suspension fluids.

At any rate, I'm not a theorist, just a dirtbiker. I only have enough knowledge of suspension dynamics to do very basic fork valving tweaks. I had a problem (that curiously developed when i put in different oil), and my research and discussions with suspension professionals helped lead me to a solution, and using a fork oil that closely matched the original in specifications was that solution. No other changes in valving, temperature, terrain or oil height were made. If my experience can be useful to someone else, that is great. If not, that is great too.

  • Justin89

Posted September 23, 2008 - 10:10 AM

#12

Okay, I talked to the guy today and he used Silkolene Pro RSF 5WT- full synthetic fork oil...that seems normal right?:excuseme: Could this all be because I went so long without having to do a fork seal change (and oil) that I just got used to the crappy old oil inside making my suspension "softer" than it really initialy was when I got it revalved?

  • grayracer513

Posted September 23, 2008 - 10:34 AM

#13

Okay, I talked to the guy today and he used Silkolene Pro RSF 5WT- full synthetic fork oil...that seems normal right?:excuseme: Could this all be because I went so long without having to do a fork seal change (and oil) that I just got used to the crappy old oil inside making my suspension "softer" than it really initially was when I got it revalved?

5wt is actually a little heavier than the factory recommended KYB/Yamaha S-1 fluid, but it should not be an issue. Most of what you see as extra stiffness/harshness is likely a result of either running your clickers so far in, or a high oil level.

If this was the first time that you've had the suspension opened up, then degradation of the original fluid fill could definitely figure into what you are seeing here. S-1 is a very, very good fluid, but not for very long. Even a very durable fluid should be changed once a year at the least.

As I said, back the clickers off to their base settings of 11 out on the compression, and 7 out on the rebound, or to the same point you ran them before the seals and fluid, and adjust from there. Also, double check with the guy who did the job on the precise amount of fluid he used in the outer chamber. If it's over 350cc, consider removing 5cc at a time, and check the results.

  • Justin89

Posted September 23, 2008 - 10:44 AM

#14

5wt is actually a little heavier than the factory recommended KYB/Yamaha S-1 fluid, but it should not be an issue. Most of what you see as extra stiffness/harshness is likely a result of either running your clickers so far in, or a high oil level.

If this was the first time that you've had the suspension opened up, then degradation of the original fluid fill could definitely figure into what you are seeing here. S-1 is a very, very good fluid, but not for very long. Even a very durable fluid should be changed once a year at the least.

As I said, back the clickers off to their base settings of 11 out on the compression, and 7 out on the rebound, or to the same point you ran them before the seals and fluid, and adjust from there. Also, double check with the guy who did the job on the precise amount of fluid he used in the outer chamber. If it's over 350cc, consider removing 5cc at a time, and check the results.


Okay thanks for the tips Gray:worthy: I guess I've been a horrible father in the suspension department:bonk: :excuseme:

  • llamaface

Posted September 23, 2008 - 11:33 AM

#15

Okay, I talked to the guy today and he used Silkolene Pro RSF 5WT- full synthetic fork oil...that seems normal right?:excuseme: Could this all be because I went so long without having to do a fork seal change (and oil) that I just got used to the crappy old oil inside making my suspension "softer" than it really initialy was when I got it revalved?



Peter verdone's chart shows silkolene pro rsf 5wt is rated at 22.3 cST (centistokes, don't ask me to explain units), which is significantly heavier than I have generally seen recommended for cartridge forks.

Not sure which yamaha is which, but the chart I linked to shows yamaha 01 fluid for kayaba's at 15.6 cST.

Those numbers almost exactly mimic the numbers I had, and the symptoms I had. If it turns out that the yamaha fluid in question is the one I found in the chart, then I would find some of that fluid, or something else in the 15-16 cST range (like motorex 2.5w, showa ss05, racetech light us1, torco rff7, or whatever) and try that instead.

Note that I am not an expert, simply someone who had the exact same symptoms you did, and found a way to fix them, with help from some suspension experts on ktmtalk. It's perfectly plausible that your problem is something else and imho grayracer's suggestions are also very sensible for you to take into consideration when trying to fix your problem.

Edit: Note that what I've read suggests that the oil viscosity mostly effects the 'low speed damping that is controlled by a variable orifice'. That sounds like it means before the shims really open up, and once the shims start working, then viscosity is much less important. Perhaps someone smart with suspension theory AND practice would know more about that, but what I felt in my forks was mostly the initial movement being harsh and transmitting too much shock to my hands, and also unbalancing the bike front to rear, so the rear felt too soft as well.

  • grayracer513

Posted September 23, 2008 - 01:41 PM

#16

Yamaha Suspension Fluid 01 and Suspension Fluid S1 are two different fluids. Neither KYB nor Yamaha list the viscosity of either fluid. S1 is lighter. However S1 costs around $30/quart, and as I said, doesn't last acceptably well.

If you visit with the guys in the suspension forum, you'll find that among "conventional" suspension fluids, Amsoil Shock Therapy is highly regarded, as are a few others.

If you really want the best fluid for the KYB twin chamber fork, switch to 215.VM2.K5 from Smart Performance. It's a completely different fluid concept from the run of the mill, and to say that it works well in a YZ is an enormous understatement.

The "variable orifice" mentioned is the bleed off passage controlled by the clickers, and any dependence on that for low speed damping is entirely the wrong approach. Use of user variable orifices should be minimized to the greatest achievable extent so that the valving is brought into play as quickly as possible. Ideally, the fork should be valved so that when at the venues where the most damping was needed, the bleeders would be totally closed. Using excessively large bleeder openings delays the correct function of the valving, and makes the fork more subject to variations in viscosity than it

  • llamaface

Posted September 23, 2008 - 02:14 PM

#17

The "variable orifice" mentioned is the bleed off passage controlled by the clickers, and any dependence on that for low speed damping is entirely the wrong approach. Use of user variable orifices should be minimized to the greatest achievable extent so that the valving is brought into play as quickly as possible. Ideally, the fork should be valved so that when at the venues where the most damping was needed, the bleeders would be totally closed. Using excessively large bleeder openings delays the correct function of the valving, and makes the fork more subject to variations in viscosity than it


:excuseme:
Maybe this is the wrong place to ask this question, but as long as you opened the door, I am only marginally familiar with how forks really really work. How do the bleeders actually 'close' during operation?

I have always operated on the idea that if the clickers end up somewhere in the middle of their settings and you're happy, then the valving is probably close. The professionals who have worked on my wp forks (which seem to be similar to yamahas WR forks) have done them so that 15-20 clicks from full in (hard) is about the right range, with 20 clicks being more of the plush low-speed rocky woods setting, and 15 more of the desert setting. It seems like if you have to go much more than 20 clicks out from full hard, that there is too much bleed and the forks start falling through the stroke and othewise doing funny things.

thanks for your insight...

  • grayracer513

Posted September 23, 2008 - 02:54 PM

#18

:excuseme:
Maybe this is the wrong place to ask this question, but as long as you opened the door, I am only marginally familiar with how forks really really work. How do the bleeders actually 'close' during operation?

They don't, unless the bypass circuit includes a speed sensitive device such as a check plate. The controlled orifice is simply opened or closed by the user in setting the clickers. But one does, as you pointed out, use varying settings for different venues. The valving is ideal when it is right with no bleeders at all, or at least very little. This forces the valving into play earlier with less movement, and gives you better control over the damping. Ideally, the valving would be set up so as to use minimal clicker openings at those times that the most damping was required so that the clickers could be opened as little as possible during times when less damping was needed.

You have referenced the WP fork a time or two, here, and as you noted, it's a different fork. There are a lot of very good discussions going on in the suspension forum concerning that fork that may interest you, and involving some very skilled tuners, many of them pros. You might want to look in.

  • MAD_POTTER

Posted September 23, 2008 - 07:13 PM

#19

Justin, I would be curious as to why the tuner thought he made the forks softer by going to 5 clicks instead of your 10 clicks and why he thought it was needed. Sounds to me like he didn't know what he was doing.

  • aggiemoto99

Posted September 23, 2008 - 07:16 PM

#20

Dont forget your compression adjuster and rebound adjuster purely effect an orifice. So if you can feel 2 clicks change, you can feel a thicker or thinner viscosity much the same.

However Grayracer is very correct it has less effect with the shims.


As to feeling stiffer, when doing purely seals on a TC fork, you don't mess with any of the valving. you dont even have to open the inner chamber and change its fluid to do just seals.

Maybe your imagining its stiffer, or it's not installed correctly, or the 5 clicks stiffer is making it 5 clicks stiffer.

But dont bash the guy because you think he messed something up. It would be very hard to mess anything up doing purely fork seals....





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