dyno of a mid valve (comp and reb)

[kawamaha]

This is a dyno of a stock YZ250 ’06 mid valve.

Shim stack: I used the stock setting of a '06 YZ250:

Comp:

0.3 float

20 .1 (3)

18 .1

16 .1

14 .1

11 .3 (2)

17 .3 (2)

Rebound:

20 .1 (5)

13 .1

18 .1

16 .1

14 .1

12 .1

10 .25 (2)

bypass (controlled by rebound clicker)closed.

Test circuit: I did not do this with the entire fork because the standard hydraulic machines I use would be too slow to test high speed movements. Instead I used the Variable displacement pump of theese machines and lead the oil through the shim stack. The more oil flow (Q) you have the higher is the pressure (p) at the shim stack. The turbine becomes inaccurate at values lower than 4 l/min (equal to 0.2 m/s) so don’t trust the rebound curve below 0.2m/s

On the dyno you see the oil flow (Q) which I converted to velocity in m/s from left to right and the oil pressure (p) in bar (1bar = 14.5psi) from bottom to top

The KYB inner chamber has 24mm diameter and the piston rod has 12.5mm diameter. with 300mm of travel we have 135.6cm³ - 36.8cm³ = 98.8cm³ of oil flowing through the MV. if the fork moves 300mm in 1s (0.3m/s), we have an oil flow of 5.9 l/min (98.8cm³ x 60 = 5928cm³).

Nothing really unexpected to see there but nice to have:ride:

[mog]

would love to see a modern crf/rmz one to compare it to.please please please

[455]

The compression side looks to be very linear.

[MRW]

Cool! I wonder what a dual stage MV would look like.

Hey, is that flat spot in the very beginning of the compression curve, the float?

[kawamaha]

would love to see a modern crf/rmz one to compare it to.please please please

do you know the ID of the showa chamber? KYB has 24mm, if the showa has another ID i have to make an adapter. usually i get many showas for service so i wait for the next one to do a dyno - but i don't know when...

Hey, is that flat spot in the very beginning of the compression curve, the float?

yes, there is a small 1.0mm bybass hole too but the most influence has the float, which is 0.3mm, not 0.25mm

[huskie]

Pls do the same test with an altered midvalve. I wld, and i feel many with me, like to see what influence smaller float, more or less shims, have on the pressure data.

Kawamaha, this yr next great post, thx:thumbsup:

[mog]

well lets just keep the kyb midvalve if you dont have a showa handy and make the shim stack like a showa,

20.1(4)

17.1(4)

0.2mm float

and retest that setup.

[kawamaha]

Pls do the same test with an altered midvalve. I wld, and i feel many with me, like to see what influence smaller float, more or less shims, have on the pressure data.

Kawamaha, this yr next great post, thx:thumbsup:

maybe i do some tests with another shim stack configuration but i think i know the results. the more shims we have the steeper the curve will be. if we change the float just move the entire curve to the left (less float) or to the right (more float)

well lets just keep the kyb midvalve if you dont have a showa handy and make the shim stack like a showa,

20.1(4)

17.1(4)

0.2mm float

and retest that setup.

what size of clamp shim is in use? there is another thread

https://www.thumpertalk.com/forum/showthread.php?t=637272

and there are 8 and 10mm shims but i dont know which

[mog]

it clamps on a 8mm i beleive.

[kawamaha]

it clamps on a 8mm i beleive.

hmm, i think that's impossible because the shims have ID 8mm and would slide over a 8mm clamp so i take a 10mm clamp. the newer CRF's seem to have 6 20mm and 1 17mm shim and a 9.5mm clamp but due to lack of shims i will try your setup soon

[455]

hmm, i think that's impossible because the shims have ID 8mm and would slide over a 8mm clamp so i take a 10mm clamp. the newer CRF's seem to have 6 20mm and 1 17mm shim and a 9.5mm clamp but due to lack of shims i will try your setup soon

Mogs mid valve stack is a common one from Factory Connection and some std Showa set up's, so yes try that with the 10mm clamp.

[MRW]

Yeah, lets get that Showa MV dialed in just like the KYB. Then we just pull some HS from the Showa`s BV and BOOM we have Showa`s that work as good as the KYB`s!!

popcorn.............

[455]

Yeah, lets get that Showa MV dialed in just like the KYB. Then we just pull some HS from the Showa`s BV and BOOM we have Showa`s that work as good as the KYB`s!!

popcorn.............

IM way ahead of ya.?

[MRW]

IM way ahead of ya.

I`ve been machining base plates for two years now:ride: Top Secret:crazy:

[kawamaha]

Now i did a comparison between a KYB and a Showa mid-valve. Though the Showa has just 0.2mm float while the KYB runs with 0.3mm float, the pressure curves are almost the same. There is no sense to show the dyno here because the little difference you could see could be also inaccuracy of the measurement, especially the flow turbine is not very accurate at low oil flow.

Maybe we can feel a small difference of theese two that i cannot measure with this method.

Another test with the stock float of 0.3mm of the KYB reduced to 0.2mm shows a little increase of pressure over the entire curve, so it is assumed that at least low to mid speed both KYB and Showa are nearly the same. I didn’t have a genuine Showa valve so i wouldn’t say anything about high speed due to the fact the shims were stopped by a block (on the KYB it’s the two 17 .3 shims)

Of course my target is to test the complete cartridge or maybe a complete fork leg but the effort is very high. Maybe somewhere along the way:thinking:

[mog]

well i thank you for your efforts ,and all information is a gain in my opinion.

[huskie]

So, no big secrets then.

I wld like to see a midvalve without shims. What curve that wld give?

My thoughts: just a flatter curve:prof:

I am editing this post as i was thinking in putting the two graphs, the basevalve and the midvalve graph, over each other to see what gives, and the funny is, the midvalve is only untill 6m/s rod speed where the base goes as high as 40m/s. Got me thinking when rodspeed are that high the midvalve will see probably a steeper angle in the pressure curve, and things will change dramatically.

Kawamaha can you get some data at 20m/s speeds with that midvalve for comparesing sakes.

[kawamaha]

So, no big secrets then.

I am editing this post as i was thinking in putting the two graphs, the basevalve and the midvalve graph, over each other to see what gives, and the funny is, the midvalve is only untill 6m/s rod speed where the base goes as high as 40m/s. Got me thinking when rodspeed are that high the midvalve will see probably a steeper angle in the pressure curve, and things will change dramatically.

there are 2 reasons for that. first i run different tests, this one with a turbine that allows not such high oil flowes but is more accurate than just with a Variable displacement pump.

second the MV has much more oil flow at the same rod velocity - if we have an oil flow of 80 l/min then we get a rod speed of about 10 m/s with the BV and just 4 m/s with the MV.

well, sounds interesting do test both KYB and Showa at high speed, when the block shim (or how do we call that) stops the bending of the shim stack. then you are right and we will see a steeper angle of the curve. but for that i have to use an original Showa stack

[russ17]

Cool! I wonder what a dual stage MV would look like.

float?

I am with MRW on this one. I would be curious if it would show a flat spot during the cross...similar to the float:applause:

[russ17]

maybe i do some tests with another shim stack configuration but i think i know the results. the more shims we have the steeper the curve will be. if we change the float just move the entire curve to the left (less float) or to the right (more float)

what size of clamp shim is in use? there is another thread

https://www.thumpertalk.com/forum/showthread.php?t=637272

and there are 8 and 10mm shims but i dont know which

Well I think you could show, the relationship between float and clamp size. basically to see if they in some way even out. Smaller float, smaller clamp verses bigger float bigger clamp. naturally this would have to be done with the same stack.. Once again