opinions on my valve stack

[4banger]

I tore the forks apart(1998 YZ400f) and looked at my shim stack. This was what was in there starting from the valve down.

One 12x.10
Ten 24x.10
One 22x.15
One 20x.15
One 18x.15
One 16x.15
One 14x.15
One Base 18x.50

It was set up for MX(supposedly a pro mxer) before I bought it and I thought it unusual for there to be a small shim on the valve face. I rearranged the stack some and replaced some shims. It is better at slow speed, but still deflects.

My Stack

Five 24x.10
One 14x.10
One 12x.10
Two 24x.10
One 22x.15
One 20x.15
One 18x.15
One 16x.15
One 14x.15
One 12x.10
One Base 18x.50

I just tried it out and am going to try a different stack when I take them apart soon. Any pointers would be appreciated. Also, the fork springs had six hash marks on the bottom. Any thought about what that indicates.

Mark


[This message has been edited by 4banger (edited 02-04-2001).]

 

[mxneagle]

The 12x.1 on the original stack is basically giving the bike free bleed at low speed. For general outdoor MX we usually run a 2 stage stack with 1 breaker shim. It looks to me like you don't have enough LSC. Pull out the 12 and 14 breakers and replace with a 16 or 17 x .1 and go up to about 10 24 x .1's on top. You may need to do a little work on the HSC stack also. I'd guess that your forks are hanging down into the mid stroke and feeling harsh. Try an oil level of about 70mm (measured by extending the forks first to remove the oil in the overlap area and then sucking out the excess)

I'm not sure about the spring markings but if you look back in the previous posts for spring design you can run thru the formula there and get a pretty good estimate of the spring rate.

 

[4banger]

Thanks for the reply. It does need some work, but I forgot to mention that I only race HS and trail ride(intermediate, 220 lbs). No MX, only a few fun jumps here and there. Would it be reasonable to assume that the 98 yz400 valve and the 00 wr400 valve are the same design and size? I saw a post earlier with the stock 00 wr400 stack. I really would just like to have it controllable and workable in the woods for now. I don't want to put a bunch of money in this bike, when it really is hard to ride in the woods anyway(due to gearing and weight). Also, any inexpensive places to buy shims?

 

[Jeff Howe]

Stock KYB fork pistons are all the same. Try out JD's stack. mxneagles suggestion is good also. You keep playing and you'll get it.

 

[Jeff Howe]

Ummm.. I should clarify that a bit more. The stock KYB fork pistons from 98 to current are all the same.

 

[4banger]

Thanks Shocknut

 

[drehwurm]

Servus Shocknut,

The stock KYB fork pistons from 98 to current are all the same.

I seem to recall that the 2001 Yamaha KYBs use an 8 port design instead of the previous 6 ports - but I'm not sure where I've read this.

Michael

 

[drehwurm]

Servus Mark,

One 22x.15
One 20x.15
One 18x.15
One 16x.15
One 14x.15

Those 0.15 shims on the HSC stack seem pretty strong to me - I'd gradually replace them with 0.10s from top to bottom till the deflecting stops or the forks get too soft for your weight. JMHO!

Michael

 

[will pattison]

for what it's worth, i just revalved my '99 yz400 forks with mx-tech's help, and the stock base valve stack has 10 of the 24x.1's on the valve face.



------------------
will pattison
engineer, racer
ignition
www.ignitioninc.com

 

[will pattison]

i forgot, i also wrote down the entire stock stack for both the active and passive compression, as well as the rebound. if you want the info, email me offline.

wp.

 

[Jeff Howe]

KYB fork pistons are 4 port. Sounds to me like the numbers 6 and 8 represent the change in the number of shims being used in the CV. I've never seen a 6 port KYB fork piston, nor an 8.

 

[4banger]

Thanks Michael and Will

 

[drehwurm]

Servus Shocknut,

I may have mixed up 6 and 8, but I'm pretty sure the 2001 Yamahas feature a new base valve design. Must be 6 port then.

Have you had apart a 2001 Yamaha KYB yet?


Michael

 

[Jeremy Wilkey]

Michael,

Shocknut surely has had a 01 appart and I will back him up.. The KYB's have never had anything other than a 4 port on current forks..

Jer

 

[c3hammer]

Isn't 4bangers stack one for tight woods and rocks at relatively slow bike speeds?

Super soft low speed with a good dose of highspeed compression.

Some guys I met from the Oregon coast range run this type of thing. Sucks up the rocks and such at lower speeds but then when you hit a big ditch or such at speed it will bottom less. Useless in the sand and higher speed desert, though.

I rode with a guy in Idaho last fall who had a WR400 set up like that. It was killer on the tight rocky single track side hills.

But as Jeremy and Shocknut know, I'm pretty clueless about these things.

Pete

[This message has been edited by c3hammer (edited 02-07-2001).]

 

[Jeff Howe]

Pete,

You're no more dense than the rest of us here. Yeah soft low speed and a fairly stiff stack beyond that. Seems to me all low speed control has been bled off. I find this a very odd setup for a pro rider on a MX track. Very progressive it would seem.

There is a tuning variable in this type of setup that most are probably overlooking though. Actually, I might play with this type of thing and see what kind of results we get with it. This stack is exactly 180deg of what I like mine to be. I can't imagine pleasing anybody, let alone a pro, with this on a MX course. Particularly in utilizing a high flow piston design. Strange, but whatever works is cool.

4banger, would you mind if I asked what spring rate is in the forks? Were there any preload spacers in there with the fork springs?

 

[4banger]

The bike was revalved by PEP in 1998, before I bought it. The springs have 6 marks on the end and I don't have a clue what that means. No preload that I saw, only a rubber bumper, about 2inches, in a metal cup.