Piviot shim

[russ17]

Piviot shim or clamping shim

My boy just recently raced at the high point Gncc He complained after he was done about the high speed harshness(square edge stuff) He is riding a 03 YZ250 i have revalved it for woods. I just pulled the vavle body out to lighten the high speed, I was going to try a smaller piviot shim just to see what the effect would be. I realize by going smaller i would also soften the low speed . But when I got to the last 2 shims on the valve body it looked to me that the .14x.10 high speed shim could only bend so far over the .25x.11 piviot shim ( it did'nt look like much)before it looked like it would hit the base of the vale body and not allow the high speed cuircut to open completely which brings me to my question, is that .25x.11 enough to allow the .14 and the rest of the high speed cuircut to open fully to me it does'nt but i have alot to learn it was just my observation that i saw. I guess i will no tomorrow

 

[Jeff Howe]

It would be dependant on how the rest of the stack was built. In a really soft stack it would be possible for that to happen. Also depends on the load, of course. Being that the 11 is .25mm thick is a lot better of course then having it be .1 thick. In all reality, I doubt it's hitting but I don't know how you have the rest of the stack built. In any case it's not something you would want to gamble with since if it did contact the base plate you would get an incredible increase in damping in a hurry. Great observation though russ17! Not too many people have a 10mm shim on hand, and I can assure you that 11 is plenty small enough for woods work if you get the rest of it right. Also, if you color the baseplate with a marker or some Dykem it will reveal if the 14 is indeed contacting the baseplate. Then you will have your answer and know if you should look elsewhere to solve your problem.

 

[russ17]

Quote: If it did contact the base plate you would get an incredible increase in dampaning in a hurry! could that be considered harshness. thanks shocknut I have'nt been on this site long but it seems that you do not give stacks it was my curriosity on just how far a shim might bend. I will try your sugestion on marking the base plate just to see. since John Curea told me about this sight I can not get off. this is the best

 

[Jeff Howe]

Yes, you would get harshness in a big manner if that 14 did contact the baseplate. Thats a HUGE increase in stiffness coefficient dude.

BTW, whether you choose to publicly display your stack info is up to you. There is no "rule" here on it. You just won't see us industry guys doing it though.

 

[russ17]

shocknut here's a stack

.24x.1 -4
.12x.1
.24x.1
.22x.1
.20x.1
.18x.1
.16x.1
.14x.1
.11x.25
every thing works great except the high speed square edge stuff. closed the float gap in the mid I did notice it definetly felt better than the stock mid not nearly as harsh just thought I could take the rest out in the high speed part or if that .14 was some how being resticted by the face plate

thanks

 

[Jeff Howe]

Originally posted by russ17
shocknut here's the stack

.24x.1 -4
.12x.1
.24x.1
.22x.1
.20x.1
.18x.1
.16x.1
.14x.1
.11x.25
every thing works great except the high speed square edge stuff. closed the float gap in the mid I did notice it definetly felt better than the stock mid not nearly as harsh just thought I could take the rest out in the high speed part or if that .14 was some how being resticted by the face plate

thanks

Marcus can handle that. Give it to him baby!

 

[marcusgunby]

Russ I was wondering if the 14mm could bend over the 11 and touch but after cahtting with a few contacts we came to the conclusion it wont.

How about trying 17/15 cobination instead of a 18/16?
That stack you posted would work for me but i race mx.

I think some of the problem comes from the stiffer frames on the latest YZs-a fair few riders cannot get them to be just right.

 

[Jeff Howe]

Another option that may be better is to remove the 24mm from the top of the HS stack. Expect a change you will feel with this, say in the neighborhood of 10- 12% or so, while the 17/15 change may be only 5% or less. I think dropping the 24 will put him as close to solving his problem as he's going to get with that stack. If after the 24 change you still want to go a little further, then play with the mid-plane shims of the HS stack.

 

[russ17]

thanks guys, I did take marcus advise and i would say it was a noticable difference. the whole time last night ( can't sleep any more I don't think i have ever used my brain so much)i was thinking of that 24. what would happen. just got back from testing its definitely better .once again thanks guys

russ17