Midvalve starting points

dbrace · May 10, 2003

Without giving away too many secrets (unless somebody wants to) what is a good starting point when tuning with the midvalve.Ive been playing with the base valve for a while and are pleased with my results, but i know the midvalve is where the magic happens.
This is no doubt going to be a long process with a full tear down needed for each change. I think it will be a great learning experience and mdvalve FLOAT and LIFT may end up being word i will love to hate but i know the results will be worth it in the long run.

Yoken · May 11, 2003

Very interesting subject... and long process for sure! I've seen quite a lot of posts about MV and theories, but nobody really gave away a setup and the "how it feels" on the track.

I am definitely not a suspension tuner but here are a few thoughts:

- BV and MV are working together so it might not be easy to fix a setup for the BV and than try different setups for the MV. If, like on my KTM, your MV came as a check-valve (with almost no damping control), lightening the BV stack seems to be the way to go.

- As I understand, some MV float is required for a plush ride especially on high speed choppy stuff. The values I have in mind are 0.5mm and below. If the stack is well built, I might be possible to have no float at all...

- Drehwurm apparently had successful results with an non-independent valving stack on both BV and MV...

Let's see what others might say about it.
Take care,

marcusgunby · May 11, 2003

I couldnt get the base valve soft enough when using no float so thats wasnt a option for me.I think the lower the lift the better as long as you can get the fork soft enough on the BV.I maybe going back to 0.2mm lift again soon, as im happy at present but feel it could be better.Generally i find the MV stacks too stiff and need to soften them to work with low lifts-as much as im willing to say unless you can come up with a juicy question to tease more from me.

dbrace · May 11, 2003

I never thought about a non-independant stack for the midvalve, its an interesting thought. Ihave been using non-independant stacks on the base valves with good results. Thanks for the imput guys.

bclapham · May 12, 2003

i went with a 0.5mm lift on my mid valve (01yz250). you will need to buy a load of 0.1m 8mm shims otherwise those 0.15's in the BV will be mega sttiff.

my BV is quite light, i am thinking of going 2stage and seeing what happens, i am wondering if my HSC is too stiff and LSC not enough.

didnt yamaha change the pistons in 02 i would like to see a photo, i wonder if any of the settings will transfer???

dbrace · May 12, 2003

Even with the std midvalve i was using .1 shims on the comp. stack. As we are talking such small lifts on the mv what is the best and most acurate way to measure it. I will post the std mv stack tomorrow to see if we can get some opinions and ideas flowing.

tmoney · May 12, 2003

dbrace, is the mv located in the dampening cartridge assembly? I finished the work on the compression stack but have not riden it yet. Just getting on the bike it doesn't feel much different, but I'm sure speed over the hard bumps will tell the truth. I ride a 250f 03 year and basically removed 1-24, 1-22, and 1-20 shim. If this does not work I will try to remove additional 1-18 and 1-16 shims from the stack for comparison. Left it a single stage since I clearly don't really have a clue for how a two stage reacts.

dbrace · May 13, 2003

Tmoney, yes it is located inside the cartridge and the mods you have done to the basevalve may help.
This is the std midvalve, the float i believe is .15mm. The two piece piston
has a recessed face where the first two shims on the stack sit.
.1X16 The .4x20 shim sits above the face of the piston .15mm thus
.4X20 (i hope) giving the 3.1x27 shims the above float. Shims i
3.1X27 assume would be used to adjust the float. I will leave it at
.1X24 that for now untill i hear from those in the know just in case
.1X20 i have it all wrong. Thanks.
3.3X14
.4X25
16mm collar
2.25x11

dbrace · May 13, 2003

Sorry! the collar is only 6mm tall.

russ17 · May 13, 2003

dbrace- I believe you forgot the other .1x.16 that is below the .1x.20 in the mid
Russ

bclapham · May 13, 2003

is that 0.15mm lift value correct? all of the YZ forks ive seen (01 250 2 stroke and 01 426) had something like 1.75 - 2.25 mm lift!

i would really like to see a pic of this piston and valving, i const understand how you have it typed out- surely the 20.4 is the backing plate for the float/lift spring???? then it goes something like 11.25 clamp, 14.3, 20.1, 24.1, 27.1(3) then the piston????

Bud-Man · May 13, 2003

bclapham,
I'm not sure exactly what the lift value is but I'm sure it's more like 1.5mm. I didn't measure the last one I had out but the lift is very large and similar to previous years. The '02/'03 YZ midvalve piston is very different from other years and manufacturers. It is a two piece design with two ports for both the compression and rebound faces. Even more interesting, the compression face has a 20mm diameter counter bore (or recess) that is approx. .4mm deep. The standard midvalving has a 20mm diameter x .4mm thick shim on the top of the stack! So you have what looks like a base plate on the top and bottom of the stack. The standard MV also has a 16.10 shim on the very top of the stack that I believe acts as a bleed shim. However, when assembled, the 27mm shims seem to seat against the piston face anyhow. I'm not sure exactly why Yamaha specified the 20mm x .40mm shim on the top but it may have been to increase the effective strength of the MV compression stack.

bclapham · May 13, 2003

Hey Bud-Man: thanks, thats a great description i see how it works now.

so i assume that the 20.4 shim that sits on the recess in the piston doesnt cover the compression ports of the piston, otherwise it would just be a racetech fork??????

i just wonder if this new design is responsible for these super harsh forks people are talking about on the new yz's?

thanks

Bruce

Yoken · May 13, 2003

Originally posted by marcusgunby
I couldnt get the base valve soft enough when using no float so thats wasnt a option for me... I maybe going back to 0.2mm lift again soon... as much as im willing to say unless you can come up with a juicy question to tease more from me.

Marcus,

Just a few thought:
0.2mm float on the MV is really not much. Could a 2-stage stack, without float, but with 0.2mm cross-over reach a similar effect? With of course a very light LSC and/or small transition shim OD?

What about a non-independent stack, still without float, but with the edge of the 1st shim (on the piston face) able to bend or "float" about 0.2mm with only little variation of pressure? Could we consider that as an effective float with a progressive damping on top?

Am not sure whether those are the juicy questions you exect, but just tell me if I am completely OFF, ok?

James · May 13, 2003

Interesting that this thread comes about as I have my forks apart (again) over-analyzing the mid-valve and thinking some of the very same stuff.

Good question Yoken....although I have an opinion, I am anxious to see what Marcus says.

bclapham · May 13, 2003

i would say that going to the 2 stage midvalve would start to make things a bit confusing, i am sure its much easier and quicker to stick with one midvalve and do a lot of the tuning with the passive stack wether it is single or 2 stages! maybe the 2-stage mid would blow through the stroke and just get stiff in the middle???

Jer made a good reply to one of my old threads, the midvlave lift is about the size of the port, the greater the lift value the quick the size of those ports increases as we push the oil through, before the shims even start to bend.

James: i assume you are talking the showas??? so where are you going to start with the lift on this midvalve??? i recon 0.2-0.5mm is a good point to start on the KYB, i thought the 0,2mm on my showas was a real small value.....until Jer expained the above! the ports on my RM showas are massive, i would love to have a aftermarket piston to compare with!

marcusgunby · May 13, 2003

Yoken i think a 2 stage mid may work better with no lift at all and a 0.2mm transition shim(or non independant type stack), but i wonder if this will stress the shims too much.I have a non independant base valve setup in there at present and its hard to see how i could go much softer on that-dont forget about seat pressure-once we have super soft base valves the clicker doesnt really have much effect. I was looking at a 03 KX base vlave i have done and im really concerned the stack bends over and touches the 2 washers under the stack-these will then become the clamp shim instead of the 11.2. I think i need to get some 11mm spaces made to act as a clamp shim-i would think it needs to be 11mm o/d and 3mm tall.
Also on the KX midvalve it has a 10mm clamp shim so thats really small compared to a YZ(yz also has bigger cartridge)

As to the std 03 YZ setup-i think its probably the worse design ever-i would prefer a check plate as at least you know what you are dealing with-the YZ mid is a checkplate made to look like a shim stack.I wonder if it was a wise decision to goto a 27mm shim that seems unable to cope with the conditions its used in.

dbrace · May 13, 2003

Marcusgunby, please help a novice out. If my float measurment is wrong please tell me how it should be measured.

marcusgunby · May 13, 2003

dbrace what i usually do is manipulate the midvalve with my fingernails from closed to open-then find a suitable place to measure the amount of movement the stack has(taking the spring out helps).It is very hard to get a exact measurement on any midvalve(and the yz mv is harder than most)and i dont beleive its necessary to get too preoccupied to within 0.1mm differences in float.You can calculate the float from each shim thickness and the post height, but im not convinced this gives a better reading than measuring it, i say this because 10 shims stacked together gives a different thickness than the sum of each.

bclapham · May 13, 2003

the easiest way i found was to disassemble the piston and then measure the distance from the back of the piston (rebound side) to the top of the midvalve post. then i put the stack on the post and measure from the back of the piston to the top of the shims- you can press the caliper quite tight to get a real good idea. then subtract the two.

russ17 · May 13, 2003

Bruce ! there was a post not to long ago with a pic of the new yz mid.I think it was the post on drilling the peens out of the cartriadge. the porting on the YZs is toward the outer edges of the piston so the .20x.40 is not suppose to effect the comp,(but IMO it does) but is there to keep the .27s from stressing in ward as bud man said because of the recess comp face. Good stuff keep it going

russ17 · May 13, 2003

Bruce sorry the pic of the two piece mid is in the thread on midvalves go back to page 9 and open the midvalve thread up it is on pg 3 of that thread called the scary one I believe marcus threw that one up

James · May 13, 2003

Bruce

I had a no lift stack all figured out and then I realized that the lift is there for a reason. I have a hard time figuring out how any 0 lift midvalve is going to flow fluid as desired without wearing the shims quick like Marcus mentioned.

I need to carefully measure the stock lift before I figure out where to go with it. I spent most of the day coming up with a way to measure it. I like your method the best.

JohnScott · May 14, 2003

Bruce & Marcus, are you guys using the stock post/collar in your MV mods [on YZ KYBs] and using small shims to lessen your lift or are you obtaining/machining new collars?

Thanks,

John

dbrace · May 14, 2003

A mate of mine has a set up from R$3 , and he was told to remove the .1x16 from the mv combined with an even stiffer bv. Man was that thing hard. But that raises a good point . Our tracks in oz are 2nd and 3rd gear with shorter straights and tighter turns. Because we are so stop start (so to speak) our tracks may have more bumps entering and exit corners.

Midvalve starting points

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