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Old 09-06-2011, 06:01 PM   #16
trailtrick
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Originally Posted by slackmeyer View Post
Thanks a bunch Javier-

I went down to look at the midvalve shims- I wasn't sure if any damage would be visible, but it's clear that at least one shim is pretty well cupped:



I'm planning on keeping notes over a few changes.
they are all cup just the face shim is the most noticiable.
Iff you are in bakersfield ,drive up to frazier pick up some shims, bring the mid valve holders and i machine theme for you and set you up.
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Old 09-06-2011, 10:06 PM   #17
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Originally Posted by trailtrick View Post
they are all cup just the face shim is the most noticiable.
Iff you are in bakersfield ,drive up to frazier pick up some shims, bring the mid valve holders and i machine theme for you and set you up.
Wish I could, but that's a 9 hour drive for me. . . . . Guess I should order some more shims. . . .
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Old 09-22-2011, 11:37 PM   #18
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Quick update:
Just got the forks back together today (finally), took a short ride on the street. Much improved. After some looking around though, I think I want to find some better fork oil- this stuff (Maxima 5w) feels too thin, especially when warmed up. I looked at some info on fork oil tonight, looks like I should track down some silkolene rsf or some redline suspension fluid, both much more stable.

As far as the feel today: high speed compression seems to be about where I want it- much more controlled, but not harsh. Low speed- I could still use a bit more damping, but I'll try a different fork oil before I change shims around. I ended up with about 1.05mm of float on the midvalve, and I got the sense today that I may have been happier with something less than that, or the heavier shims that Javier recommended.

more later. . . .
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Old 09-23-2011, 06:07 PM   #19
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Excellent thread - thanks for taking us along. I'm learning...that I don't know crap!


But that's good. That's why I'm here.
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Old 09-23-2011, 10:45 PM   #20
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Originally Posted by Chuckracer View Post
Excellent thread - thanks for taking us along. I'm learning...that I don't know crap!


But that's good. That's why I'm here.
Feel free to ask questions. I'm not sure that I can answer them correctly, but we'll all learn from the experience, I'm sure. I put this thing together cribbing off of other threads like this one, plus some figuring some stuff out based upon the problems I was having with stock valving. It's starting to seem a lot more straightforward to me at this point.

Ordered some Redline medium suspension fluid today, should be in tomorrow. It's supposed to be around a 10 weight, but the key is that it's much more stable with temperature increases. My takeaway from fork oil research was to use redline or Silkolene rsf, or Mobil one ATF (if you want a heavier weight oil, it really is pretty good). Mobil1 seems to be around 15w, heavier than a person should need if the valving is doing it's job.
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Old 09-24-2011, 03:56 PM   #21
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I'll ask one:

What is "float"? I've tried & tried to figure it out by context, but no luck.
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Old 09-24-2011, 06:12 PM   #22
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I'll ask one:

What is "float"? I've tried & tried to figure it out by context, but no luck.
Ok, I'll take a crack at it- the damper rod of the fork has a rebound shim stack (the delta shims and others in that series that you can see in the photos) and a compression stack (really more of a check valve, it's just 4 24mm shims with a spring behind). There is about 2.0mm of 8mm shaft between the valve body and the shoulder of the rebound tap. The shims take up 0.4mm of that length, leaving 1.6mm of "float" in which they can move, with only spring resistance, before the shims need to bend to accommodate higher oil pressure.

When the damper rod is travelling down (compression stroke), the valve body lets fluid flow through against those 24mm shims. Increasing the amount of float will reduce compression damping (especially low speed), decreasing the float will do the opposite. As long as fork oil pressures (set by the speed of the fork leg travel) stay low, very little or no oil will be pushed through the base valve, which contains the main compression stack on this bike.

Here's a little illustration from Racetech: this illustration shows a check valve instead of a mid valve, but just imagine that the check valve consists of a shim stack with a carefully set amount of float before the shim stack comes into play:
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Old 09-25-2011, 04:46 PM   #23
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Originally Posted by trailtrick View Post

few thinks you want to think in consideration is
#1 how much plushness you want to sacrificate for precision and find the balance you want mid valve/base .

# 2 find the stacks the make the base and mid valve work in armony together
Hope you don't mind me asking a question but how do you balance the mid valve and base valve? What is the aim i.e. do you want low speed oil flowing through the mid and high speed oil through the base (and a bit of mid)? Or equal? What are the trade-offs?

Another Q - That large amount of float will reduce the effectiveness of the compression clicker will it? i.e. even fully in (hard) there is plenty of scope for oil to flow around the midvalve/float?

OK last one - have been wondering about this, how do you set the balance between spring stiffness and compression damping?
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Old 09-25-2011, 07:05 PM   #24
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Originally Posted by men8ifr View Post
Hope you don't mind me asking a question but how do you balance the mid valve and base valve? What is the aim i.e. do you want low speed oil flowing through the mid and high speed oil through the base (and a bit of mid)? Or equal? What are the trade-offs?
I don't think I really know how to balance the mid valve and base valve, other than to imitate successful stacks and take advice from people like Javier- .6-1.0mm of float seems to be the desired amount. There are some who like a clamped midvalve (no float), but they are a minority.
From what I understand, the mid valve stack lets low speed oil flow through with very little damping, and has the most effect at medium oil speeds. At higher speeds, more oil is being forced through the base valve, because the midvalve can only flow so much oil. So the effect of reducing float and increasing the stiffness of the shim stack is increasing the damping of the oil at the midvalve as well as increasing the flow through the base valve.

Quote:
Another Q - That large amount of float will reduce the effectiveness of the compression clicker will it? i.e. even fully in (hard) there is plenty of scope for oil to flow around the midvalve/float?
Yes, both the float and the clicker mainly affect the low speed compression damping, because the size of the orofice that oil has to pass through to get to the adjustment mech. To the question about plenty of room for oil to flow around through the midvalve. . . . it's a question of how you want your suspension to behave. But for me, the answer is yes, there was too much oil flowing around the valves even with the clickers at full hard.

Quote:
OK last one - have been wondering about this, how do you set the balance between spring stiffness and compression damping?
Don't know that one for sure, but as I look at lots and lots of shim stacks for the WP 48 forks, built for bikes from 200 EXCs to 450 SXs to 950 ADV, I think more and more that the valving is for terrain/way you ride, and the spring rate is based upon the load on the fork. You can't substitute one for the other, and you can't have one of the factors right, and the other wrong, and expect the suspension to perform to it's fullest.

Edit: and I know you pointed that question towards Javier, and hopefully he'll answer it too.
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Old 09-26-2011, 06:19 AM   #25
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Originally Posted by slackmeyer View Post
Ok, I'll take a crack at it- the damper rod of the fork has a rebound shim stack (the delta shims and others in that series that you can see in the photos) and a compression stack (really more of a check valve, it's just 4 24mm shims with a spring behind). There is about 2.0mm of 8mm shaft between the valve body and the shoulder of the rebound tap. The shims take up 0.4mm of that length, leaving 1.6mm of "float" in which they can move, with only spring resistance, before the shims need to bend to accommodate higher oil pressure.

When the damper rod is travelling down (compression stroke), the valve body lets fluid flow through against those 24mm shims. Increasing the amount of float will reduce compression damping (especially low speed), decreasing the float will do the opposite. As long as fork oil pressures (set by the speed of the fork leg travel) stay low, very little or no oil will be pushed through the base valve, which contains the main compression stack on this bike.

Here's a little illustration from Racetech: this illustration shows a check valve instead of a mid valve, but just imagine that the check valve consists of a shim stack with a carefully set amount of float before the shim stack comes into play:
Thanks for explanation, Zak, but I'm still pretty mystified.

What is that check/ mid valve attached to, or does it just float in the fork leg?

Also, it looks from the cutaway view that the damper rod assembly would hit the nut/bolt on the check valve when it travels downward if the check valve is indeed attached to something. If the check valve does float, it doesn't seem like it would have much of an effect on fork operation, but then it wouldn't get hit by the damping rod, either.

Ye Gods!

I'm not a mechanical moron, but forks seem to me like an automatic transmission with the mysterious processes happening within.
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Old 09-26-2011, 08:49 AM   #26
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Originally Posted by Nailhead View Post
Thanks for explanation, Zak, but I'm still pretty mystified.

What is that check/ mid valve attached to, or does it just float in the fork leg?

Also, it looks from the cutaway view that the damper rod assembly would hit the nut/bolt on the check valve when it travels downward if the check valve is indeed attached to something. If the check valve does float, it doesn't seem like it would have much of an effect on fork operation, but then it wouldn't get hit by the damping rod, either.

Ye Gods!

I'm not a mechanical moron, but forks seem to me like an automatic transmission with the mysterious processes happening within.
The rebound piston, with the mid-valve shims on the top side, and the rebound shims on the other side, is part of the damper rod assembly. The end of the damper rod is threaded and the piston slips on and is held on by a nut.
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Old 09-26-2011, 05:39 PM   #27
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Originally Posted by Nailhead View Post
Thanks for explanation, Zak, but I'm still pretty mystified.

What is that check/ mid valve attached to, or does it just float in the fork leg?

Also, it looks from the cutaway view that the damper rod assembly would hit the nut/bolt on the check valve when it travels downward if the check valve is indeed attached to something. If the check valve does float, it doesn't seem like it would have much of an effect on fork operation, but then it wouldn't get hit by the damping rod, either.

Ye Gods!

I'm not a mechanical moron, but forks seem to me like an automatic transmission with the mysterious processes happening within.
Look at the first picture in this thread again- it'll help if you've had your own forks apart, too.

The bottom row of shims and a valve body are all the base valve- it stays in one place, screwed in the bottom of the fork right by the axle.

Everything above that is part of the damper rod assembly- it all goes up and down, attached to the upper fork sliders. That valve acts both as a rebound/compression valve and as a piston to push oil through the base valve.
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Old 10-18-2011, 10:11 PM   #28
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Originally Posted by slackmeyer View Post
Feel free to ask questions. I'm not sure that I can answer them correctly, but we'll all learn from the experience, I'm sure. I put this thing together cribbing off of other threads like this one, plus some figuring some stuff out based upon the problems I was having with stock valving. It's starting to seem a lot more straightforward to me at this point.

Ordered some Redline medium suspension fluid today, should be in tomorrow. It's supposed to be around a 10 weight, but the key is that it's much more stable with temperature increases. My takeaway from fork oil research was to use redline or Silkolene rsf, or Mobil one ATF (if you want a heavier weight oil, it really is pretty good). Mobil1 seems to be around 15w, heavier than a person should need if the valving is doing it's job.
Finally got out for a ride (well, commuting to and from work the long way, maybe 40 miles) on the forks with the redline oil. That was definitely what I was looking for. I just set the clickers in the middle of their range when I put it back together- I'll test the whole range when I get some time, but I'm pleased as punch for now. Much less wallowy, and no sinking on the hard turns. It's less plush feeling on the bumps, but way more controlled. I need to find someone else to ride this thing and confirm my impressions.
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Old 10-19-2011, 08:56 AM   #29
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Originally Posted by slackmeyer View Post
Finally got out for a ride (well, commuting to and from work the long way, maybe 40 miles) on the forks with the redline oil. That was definitely what I was looking for. I just set the clickers in the middle of their range when I put it back together- I'll test the whole range when I get some time, but I'm pleased as punch for now. Much less wallowy, and no sinking on the hard turns. It's less plush feeling on the bumps, but way more controlled. I need to find someone else to ride this thing and confirm my impressions.
I wish I could, because I'm not all that excited about my suspension after riding a buddy's Ohlins-equipped GS. Yeah, that's right-- a GS. I couldn't believe how great that German Suburban felt at speed on a dirt road, and how crummy mine felt in comparison. I actually nicknamed Marc's GS the "Magic Carpet" after that ride.

I haven't found an appropriate nickname for mine yet, although I'm leaning toward "Half Tube of Toothpaste" or "Brown Banana."

Thanks for all the info about forks, by the way.
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Old 10-19-2011, 05:29 PM   #30
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I wish I could, because I'm not all that excited about my suspension after riding a buddy's Ohlins-equipped GS. Yeah, that's right-- a GS. I couldn't believe how great that German Suburban felt at speed on a dirt road, and how crummy mine felt in comparison. I actually nicknamed Marc's GS the "Magic Carpet" after that ride.

I haven't found an appropriate nickname for mine yet, although I'm leaning toward "Half Tube of Toothpaste" or "Brown Banana."

Thanks for all the info about forks, by the way.
Do you know what you're running now in the forks? Have you changed the oil or springs? For about the price of a front tire, it's definitely worth replacing the springs with heavier ones and changing the fork oil to something in the 10-15 weight range- synthetic ATF is really not a bad choice for the stock valving. My stock fork worked a lot better with royal purple ATF (couldn't find Mobil 1 locally) than it did with maxima 5 weight.

Hope you get your ktm problems sorted out- and ohlins are a pretty high bar to match, they really do work well.
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