Measuring Mid Valve Float...

Could someone please explain to me how to ACCURATELY measure mid valve float, or any valve float(ACCURATELY) for that matter??

 

I did a little tinkering on the mid this weekend, and it made a huge difference for the better. but just visually, and trying to physically move the mid on the post to check it for function I could tell that one stack didn't 'float' as much as the other stack. could there be the possibility that both posts aren't the same dimensions?

 

for the record, I decreased the float .15 MM, and installed a 10x17 in the mid stack. One side still had visible float, and other side was visibly tighter.

 

2006 kx450f, with gold valves. I also lightened base 2 'steps' on my chart.

 

thanks for the replies and knowledge.

Take the total of the thickness of the compression shims.

Measure the collar, and any shims that have a smaller O.D. than the I.D. of the mid valve compression shims.

Then measure the recess in the M.V.

So, add the total of the collar and smaller O.D. shims. Then subtract the recess in the M.V. from that. Take the total thickness of the compressions shims and subtract that from the total you found earlier.

Collar/small O.D. shims- M.V. recess-total thickness of compession shims= float.

ok, so its basically a (gross)measurement thing? that comes up with a (net) number "float"??

 

the mid side of the valve has a shim installed in the recess that creates '0' preload. and there is also a shim in the cup washer farthest away from the valve. I would only assume that the shim in the cupped washer is to prevent spring wear on the aluminium cup??? As I cant see how that shim can effect float?  So is the float adjusted on the valve side or the top of the stack side?

Check what is the fattest feeler gauge you can push easily in all the way to the shaft in the float gap between port and face shims. Seems to work just fine for me. There are various ways the floating shims are supported when fully compressed, but ignore that, and just gently pull a face shim down a little and insert a feeler gauge.

 

My original 06 forks were revalved by a shop and had a huge 0.6mm float with a heavy mid valve, with the small stock ports in the base piston, and they were horribly harsh to ride over sharp hits at speed.  If/when I need to reuse them again, I'd go for something with a narrower 0.2 float, a soft (near stock) mid stack, a smaller 14mm clamp under the base stack, and enlarge the ports in the base piston. The base comp adjust bleed stack is reversed (fully open) in the stock 06 forks, so I'd also swap that around into something more normal with goal being a less sensitive comp clicker adjuster. Stock 06 reb stack looks normal so I wouldn't change it if your springs are around 0.46.

ok, so its basically a (gross)measurement thing? that comes up with a (net) number "float"??

 

the mid side of the valve has a shim installed in the recess that creates '0' preload. and there is also a shim in the cup washer farthest away from the valve. I would only assume that the shim in the cupped washer is to prevent spring wear on the aluminium cup??? As I cant see how that shim can effect float?  So is the float adjusted on the valve side or the top of the stack side?

 

Midvalve float is one of those things that isn't a precise measurement.  I measure/calculate float two ways to sort of verify my results.

 

First method is with a set of calipers:

  • measure the total shim stack thickness (shims that actually float between the piston face and the cup washer)
  • measure the length of the collar and subtract the recess (for the collar) in the piston and subtract the recess in the cup washer (if it has one)

What your left with is the length of the collar exposed between the piston face and cup washer.  From that subtract the shim stack thickness and you have your float.  Then I'll assemble the midvalve (with shims) without the MV spring. Second method is with feeler gauges:

  • get two feeler gauges, the size of which you calculated earlier or just start with small ones and work your way up
  • insert them, on either side of the stack, between the cup washer and backer shim (if the stack has one, if not then the piston face and face shim)

Then it's a matter of "feel", both feeler gauges should be able to be inserted all the way against the collar with some resistance, but not too much and not enough to bend the shims.  Just realize that this float measurement is a relative measurement, i.e. you know roughly where your starting and then you can make changes to increase or decrease float.

 

As far as adjusting float, it really depends on the setup.  Washers between the collar and cup washer effectively lengthen the collar and are usually the same ID/OD as the collar.

 

  • increase the thickness of the shim stack = less float, decrease = more float
  • increase length of collar = more float, decrease = less float

If you're happy with the shim stack, you can adjust float by either changing the thickness and/or qty of the clamp shim.  You can also get a shorter/longer collar.  If you want a longer collar, another option is to install shim of the same ID/OD between the collar and the cup washer.

Thanks for the replies guys. Very useful stuff ( for me ).

 

  At what point can you tell that the mid is a good match for the base, and vise versa?  Or are all the circuits at the end of the day just a matter of feel and confidence?

At what point can you tell that the mid is a good match for the base, and vise versa?  Or are all the circuits at the end of the day just a matter of feel and confidence?

I think it's best to set the fork up with the mid being your front line defense, sometimes only damping the details, and the base doing the major grunt work.

 

The mid valve moves 1:1 with the front wheel. So it moves first and at the highest speeds. That means it is hypersensitive to changes.

 

If you ask the mid to provide too much damping (too stiff and tight) then you lose initial suppleness and you quickly run the risk of introducing cavitation on fast comp hits which means the very next rebound stroke has near zero initial damping. Result = harsh, less control and lost traction.

 

If you setup the mid valve too flexible or too much float gap, then you might as well not have it. If the mid does nothing initially then you lose feedback/feel in certain types of riding (MX).

 

Targeting a mix of trails and MX with frequent hard sharp hits, sweeper turns and mild jumps, I prefer firm springs, firm low speed damping, soft high speed and good front tire feedback when the fork is nearly fully extended. So I certainly don't like super soft base setups or wide float gap.

I think it's best to set the fork up with the mid being your front line defense, sometimes only damping the details, and the base doing the major grunt work.

 

The mid valve moves 1:1 with the front wheel. So it moves first and at the highest speeds. That means it is hypersensitive to changes.

 

If you ask the mid to provide too much damping (too stiff and tight) then you lose initial suppleness and you quickly run the risk of introducing cavitation on fast comp hits which means the very next rebound stroke has near zero initial damping. Result = harsh, less control and lost traction.

 

If you setup the mid valve too flexible or too much float gap, then you might as well not have it. If the mid does nothing initially then you lose feedback/feel in certain types of riding (MX).

 

Targeting a mix of trails and MX with frequent hard sharp hits, sweeper turns and mild jumps, I prefer firm springs, firm low speed damping, soft high speed and good front tire feedback when the fork is nearly fully extended. So I certainly don't like super soft base setups or wide float gap.

 

 

You state that too little (tight) float can cause cavitation on rebound... well.......

 

I rode the bike with the new midvalve changes and what could be possibly too little float as per my previous post.  Also softened the base a cpl steps.  Now after hitting a good jump and really wring it out because the compression is so good, there seems to be No,NONE, nadda REBOUND DAMPING... its bouncing back up and actually popping a wheelie.

 

Does this mean I have too much Mid, and not enough base, or can I get by with upping the rebound stack to compensate?  If it truly is cavitation, how can I get to the place im at without cavitation??

 

I will post stacks in just a bit... FWIW, it does have Gold Valves. so Keep that in mind. Thanks JIM

Sounds like the shims are not covering the piston properly , it doesn't sound like cavitation

You state that too little (tight) float can cause cavitation on rebound... well.......

 

Does this mean I have too much Mid, and not enough base, or can I get by with upping the rebound stack to compensate?  If it truly is cavitation, how can I get to the place im at without cavitation??

 

I will post stacks in just a bit... FWIW, it does have Gold Valves. so Keep that in mind. Thanks JIM

Previously I tried to write that a tight float AND stiff mid stack can cause cav because of too much pressure drop behind the mid piston. Both. Not just tight float.

eg.  My KXF has a narrow 0.15mm float, but with a soft stack that can bend a lot and those forks are amazing on huge fast hits. My YZ has 0.20mm float with a softish stack and I think it's plush on reb on long sections of repeat rough stuff.

As mog wrote, maybe you assembled something wrong.  With your reb clickers wound full in, do you get very slow rebound when pushing the bars? You should.

 

If your mid is too stiff, then there is a good chance you can prob get to where you are now on the comp, with less or no cav on fast sharp hits, by softening the mid and firming up your base.  What to do on each comp stack is an even bigger guess. It depends on many things like your riding, your current setup and maybe those GV pistons.

 

Personally I like a mid with tight float soft HS stack. That means those shims flex a lot and get a work out, but better them than me.  Over the years I've read here that a lot of off technical single trail guys like removing lots of face shims in their base valves and using soft springs. But for whatever reason I just hate that bouncy vague rocking horse feeling when I try to stuff the bike into a long bumpy corner berm and the front tire disconnects when I'm not ready for it. It's whatever floats your boat in the suspension world.

Edited by numroe

I will tear it apart tonight guys... snowed 6" last night, so I have time LOL...will post stacks tonight... and I'm not opposed to pulling the gold valves.  For the money, they are "informative". LOL

Ok, Here is the Rebound and Mid Valve stack...

 

Nut

aluminium washer

 

Rebound

2) 25.10

15.12

15.14

15.16

10.18

10.11

3) 10.18

Piston

 

Midvalve

50.14

30.15

10.19

10.17

8)10.19

10.11

2)31.17

10.11

collar(sleeve)

spring

11.13 im cupped washer

cupped washer

 

Nothing looked out of place in this valve. This is the valve that "appeared" to have more float than the other.

 

Although when I took the forks off. this fork seemed to have more rebound damping action. Even if it was what I would consider light when pushing on the fork by hand. The other fork didn't seem to have as much rebound damping action, and when it did finally catch the rebound it seemed like it "missed an Inch before the rebound started to dampen it... MAKE SENSE?? It actually seemed like the fork had free play until the rebound damping catches...

 

My calipers are digital and they don't seem to be more accurate than .1mm... so forgive my weird, if not correct  numbers... but they're close.

 

After looking at the numbers I had written down for the original stacks, it would appear that I "created" a triple stack by mixing up a 10.11, and misplacing a 10.19 farther down in the stack.

 

 

LOL, here nor there... that still doesn't explain the lack of rebound Damping that I experienced Sunday.

 

PLEASE HELP.

thanks JIM

The other thing I will add is that on this service I did change from BelRay 5w to KYB 01M oil inner and outer... Guess it might have made a difference.....???  I also added the 10.17 to try to stiffen it up just a bit, and I think that's where I made the stack order mistake in this fork.

Edited by kxjim

Your mid has shims listed like 50mm and 30 ? That's bigger than the outer tubes of the fork ? And your rebound is 25(2) then 15s they should be something like eg

25.1(2)

18.1

23.1

21.1

19.1

17.1

That's a really really messed up mid valve , I would phone Chris from rt and see if he can help , he posts here a lot

The first number would be the thickness, 2nd number the diameter. the rebound I never changed. The 17.1 I added to the mid, and misplaced the 11.1 in the stack... both of them should have been together. These numbers are in your format MOG.


Edited by kxjim

Nope mine is dia then thickness ;-)

kxjim, can you repost those three stacks with diam then thickness, and face shims at the top of each stack list?

ok,,, after going back out and re-measuring and re-looking. this is what I have..... I did foul up the install when I put them back together. at least on this fork. it was late, and I was hurrying... LOL, is that a reason or an excuse?

 

MID

 

14.5 in mid valve recess

15.3

19.1

17.1

19.1(8)

11.1(2)

17.3(2)

spring

collar

13.1 in cupped washer

 

 

REBOUND

 

18.1(3)

11.1

18.1

16.15

14.15

12.15

10x.25(2)

 

I installed the 15.3 in the mid to take up float. unfortunately I know now put it in the wrong place.

I also added the 17.1 to stiffen mid a bit, but also put it in the wrong place in the stack.

 

with the 13.1 in the cupped washer and the collar and the 14x.5 in the piston face.. there is 3.48 measured clearance for the mid stack to reside...

Your reb stack looks stock.  I have some 06 forks and that's what I found in them some time back. So if that's assembled right, then it should be fine.

 

Your mid comp stack looks like a mess. I'm not sure what to make of it.  Maybe you are getting cavitation. I'm not sure.

 

The 06 KX450F stock mid has 9 x 19.1 face shims clamped directly by 2 x 11.1 which sit on 2 x 17.3.  A bit weird I suppose because maybe those face shims cannot bend out of the way enough before they hit the 17. I cannot remember the stock float. For sure they are thin 0.1mm shims that's why so many. I'm not sure what you should try for the mid since I shelved those forks a few years ago. I do recall that 06 mid stack sit in there differently to the newer "SSS" type forks. 

 

If you are desperate to try something with no better suggestions, then I can only suggest/guess something like what I wrote before:

reb = stock.

mid = something more flexible with a thicker clamp allowing lots of bend at high speeds, and a tighter float gap, like 0.2mm

Base = drill out the piston ports to be much bigger. Replace the 15mm clamp with a smaller 14 or 13mm. I'd not have less than the stock 10 x 26.12 face shims, unless you'll do some lower speed trail riding.  Do the plastic free piston drill mod too. Because they can crack, and the connected air chambers softens those forks a little on big blows.

Outer oil vol = 310ml, which is low, then add if bottoming too much.

Edited by numroe

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