fork tuning for enduros

Taf,

No, I didn't know about the SX BV nuts. Have you seen them?, are they exactly the same?

Regards

Just remember that the 0.15 mm shim is RADICALLY stiffer than the 0.1 mm one. The 0.11 ones, 33% stiffer, are (only?) available as original parts for japanese motorcycles. The local tuner will probably try to sell you the 0.1 ones even if you provide the yamaha or whatever brand parts numbers (no I have not got the P/Ns). I bet he'd use them himself thinking that there is no difference. He'd typically use a vernier caliper to tell the thickness, and simply can't. But just by the feel of it in your hand you can easily tell the difference, if you've got a 0.1 as reference.
You could try and see if for instance http://www.qualitetch.co.uk/dampershims.asp would be able to supply +30% 0.11 shims (which I don't think) or the +100% 0.125 shims (which I do think that they with some persuation would). The 0.15 shims may be overkill capacity?
I wish too to cure the launching you describe. Some messing with the pudding might make it tell you what it needs. Preloading might or might not work, I don't really think it will but will try some and see what it does.

This was ground concave to give a 0.2 mm preload to the rebound stack. I won't be able to ride for a while because of an injury so dont ask what it did to the pudding.
Keep up the good work Taffy, it is always interesting to read about your findings.
Regards.

This is what the piston checkplate of the 2000 fe OEM fork became. A Mid Valve!
1 mm play on a zp3(ish) tap. (Have to check some day what zp3 actually ended up with)
People are going to smaller and smaller float, but it feels like I'd like to increase it a bit though and perhaps use a slightly heavier MV than the rather conservative one in use now:
24 0.11 Kayaba shim, Yamaha Original Parts... (For longevity. Hope it works.)
3x 24 0.1
22 0.1
20 0.1
18 0.1
Then again I might not, time will tell.
old style wire spring. Weaker than later models, it will likely be replaced next time the piston comes out, with a new style stiffer spring. People have been happier with the new spring. It should add some light digressive damping in the very low speed domain, me thinks.
Old, vintage, short and hard top-out spring, I'll keep it because of...

... the concave rebound stack valve face. The top out spring is living an easy life now, only receiving light hits, they can't even be felt. I never thought the preload would be a particularly good mod at all, but, the degree of rebound control is just unbelievable. 8O Still don't really. :roll: Believe it..., :roll:,:roll:.



Here is the rebound stack. Didn't change it, it is the same as the 2000 OEM stack. Consensus seems to be a rebound stack with considerable more shims on it, but since there is now a .2 mm concavity of the valve face the fewer shims that are in this stack (which I always liked anyway) will likely do.
Piston
24 delta
24 delta
14
22 delta
20
18
16
14
10 .3
16 .25
nut
The gap between the low speed shims and the rest of the rebound stack is hard to see in the picture. With the .2mm concavity of the piston face this gap shrunk to .05mm.
What I really wanted was a pop off characteristics of the high speed but didn't know how to achieve it, gave up and decided to try something crazy. Didn't want to try a ring shim as it makes the split stack a single stack. People have not generally been happy with ring shim preloading for enduros. The concavity is the crazy thing, it would obviously give the slow speed portion of the stack the pop off-ish qualities, but not the high speed portion. But, to my surprise, it did to some extent. When you think of it, it should be spherically preloaded too, up to the split shim diameter, and the rest of it, umm... well, the rest might be preloaded too, only conically. (?...)
Theoretically, unlike ring shim preloading, a concave valve face does not annihilate the low/high speed progression of the rebound stack. Don't know what it means in practice though...

And, to reduce any unnecessary fixed orifice damping, the piston was ported a bit as well:

Ported piston, less resistance for high speed oil flow on fast compression. More force on the mid valve shims, less on the valve. The mid valve shims can give, the valve can't, that was the whole idea with this mod. I see Taf says zp3 did this, again, I'll have to check out what else zp3 did.

The delta shims in the rebound stack could be even more "deltaed", at least 1 mm per nibble, they'd still cover the rebound ports. That would soften the rebound stack AND open the compression ports even further, all in one mod. That might be the next mod to do to the piston.

Question remains, some mods may be more of a spell than others, Two holes, Porting and Check valve nut drilling are strongly suspected to belong to this category. Just changing the oil while chanting might be just as useful. What do you think?

There are some more pics in my gallery.

Regards you lot.

Taffy, Never under estimate the placebo effect. It is a proven effect too.

I'm only pulling your leg :twisted: , it's good to have you back!, we've all been missing you for a little while now. Regards.

PS
preload = 0 mm or so, of the .44 springs.
oil level = 130 mm.
Oil = Q8 Fork Oil Light 5, 21cSt @ 40degC, V.I.=219, (Kuwait Petroleum).
Chanting seems to work, but it could also be the new oil itself.

2 holes: They bleed some of the pressure buildup from the oil shearing in the telescoping of the fork, thus relieving the seal from the increased pressure that otherwise would have made the seal grip harder on the chrome on rebound. Less friction and smoother action! Should bleed some of the suction created likewise on compression as well. Thats the area of pi x 43 x 0.5 = 67,5 mm^2 of vacuum hammering on its collapse that should be noticeable as harshness and it is reduced. Not a big area but still.

Check valve nut drilling: This may be difficult to notice, but should aid in check-valve performance somewhat. Doesn't cost anything to do if you do it yourself.

Ported piston: Moves some of the damping from the fixed aperture in the piston to all compression shims that can react to the oil pressure and moderate the damping resistance according to it. It is yet another step on the road to the smoothening of those very hard hits that tended to shake the flesh off your arms when running the 2000 OEM 43 mm forks unaltered.

Would it be possible to simply remove the 3-legged washer at the base of the hydraulic cone without ill effect? Or does it perform some very important task apart from being a spacer? It's the 3-legged washer that the spring is resting upon. What I would like to try is even less preload than zero. Like for instance 10 mm totally unsprung and free floating movement between the spring and the topout spring. The 3-legged is the only thing I can think of to increase space for the spring. Any other idea?
Just want to see what it's like...

Regards

Taffy, It is no preload when the plastic washers are gone. But no slack either. The pictures in the doc are actually quite good. Makes me wonder about the topout spring. Suppose the old fashioned short and hard spring was replaced with a newer style topout spring, which is about 10 mm longer. That would leave us with a minimum preload of about 10 mm. Not so good perhaps, might be another reason to stick to the vintage topouts... Especially since I wanted to try a 10 mm slack.
BTW, in the subtank bit in the doc there are a few pictures showing subtanks. They are fitted to a bike with the coolest looking triple clamps (yokes) ever seen. Who is making these?
Regards

It could be the preload adjusters in the caps that take up space. That could be why there is no space to spare for slack spring experiments nor new style topout springs.

Well, Iv'e got those preload adjusters and always regarded them to be the OEM stuff.,? There are a couple of nuts and stuff in there and they take up space. That could be where the space loss is. The plastic spring padding washer was only a couple of mm thick, not much more. Yours was thicker, right?, about 10 mm or so?

SB?

I'm not clear on what you are trying to fix by removing all preload?

ktmlew,

No attempt to fix anything, really.
It should have been a cheap, easy and harmless experiment. Thats all. Just wanted to see what it's like...
Might have tried it, but now that there is no space to spare I just might not bother. Doesn't matter much. Used about 4 to 6 mm of preload previously and the forks seemed happy with that. With a spin of the preload adjusters they will be there again, no problem.

Taffy,
The preload adjusters are in the doc, they took one of the nuts out, the wide one, to show the machining made for the sub tank air flow.

The general settings of the forks may be a little astray right now, but that was expected. All in all they are already a lot better than stock though. Even if I stop now, it will easily have been worth the effort.

Again, thanks for the inspiration. Without it the forks would still have been as bad as they were.

Regards

PS
May 24, 2007
Copied this from another thread, where I wrote:

Even though another 3 shims were added to the MV and the face shim was replaced with a slightly thicker one, the fork became softer. I'm now considering adding even more shims or reducing the MV play from the present 1 mm to even less, like for instance to what ktmlew suggests, 0.7 mm or so. Alternatively keep riding it the way it is, to get a better feeling for what next step would be the best. It feels like the rear is not up to it any longer, the shock might even be the next object of attention before anything else is done on the fork.

If you have left the fork problem and would like to discuss fork tuning I suggest that you move to the "Fork tuning for enduros" thread

Now as smorgasbord says let the threasd "fork problem" continue here:

I have a offer now from an WP supension specialist to do my forks.

First I will do a further trial with the tipps from taffy, smorgasbord and the doc, then I can give it to the specialist.

But anybody has a different meaning.

I trust in you and will do now this:

ZP3 mod.
MV instead of CV.
The original spring check valve can be used?

Then stiffen the rebound

I´m not sure to do any drill modes...

regards

This is the original CV spring on a modified piston tap. Well, a part of it is visible anyway, between the hexagonal part of the tap and the MV shim stack. Works fine.



Here are my taps, after and before modification. The mod is not fully ZP3, he made the shoulder, which the MV stack hits before it starts to flex, chamfered with a 30 deg angle that makes the shim stack bear at the edge of the 8 mm hole. Thus flexing more easily.


Picture from Taffys "the doc" for comparison. zp3 on the left. Later model tap on the right hand side.
Regards

Edit:
On shallow washboard bumps and acceleration when the fork was working quite extended it started to top out harshly after a number of these bumps. As if there was not pressure enough in the fork to refill the rebound damping volume at each bump. On large bumps it worked better and deeper in stroke it did. I decided that some of the damping had to move from the mid valve to the base valve in order to prevent the oil from escaping rebound volume.
MV is now at .7mm float and the following stack.
24 0.11 (KYB shim)
22 0.1
20 0.1
18 0.1
Still not a turned 8mm zp3 pivot, instead pivoting on a .60 mm wire ring cut out of an extension spring. Very simple. The MV stack is very soft. It can now flex 2.5 mm before it hits the stop. That could be shim brutality.
Rebound, most of the time, is very near what I want and don't know what else to do now, thus unaltered.

The piston is now removed for modification from the fork without removing the forks or wheel from the bike and wont even have to drop the oil. A 35mm circlip http://www.seeger-orbis.de/en/index.php?article_id=335&FORM[target_id]=28 under each BV prevent them from falling out, they grip by friction only. The cartridge tube, piston and piston rod, hydraulic bottoming cone, spring guide, spring and lid comes out as a unit. If necessary, a U shaped piece of sheet metal is installed as a temporary preload spacer so that the spring tension is rised to increase the friction in the assembly, it can then simply be unscrewed from the BV and lifted out of the fork. Or just put the spanner on the spring guide as you would anyway later. The BVs will remain in the forks, held by the 35 mm circlips, and their o-rings will prevent the oil from running out on the floor.

BV is almost the same as before but with three 24mm shims added. Nearly all shims .1 mm thick.
valve face
24
24
24
12
24
24
22
20
18
16
14
12
10 .3
18 .2
BV post

Perhaps this BV stack went a little overboard, not too bad really, but might pull one or both of the 24s between the splitter and the 22. Not sure yet if the .7 mm play MV was an improvement over the 1mm one. Might even go back to previous stacks and grind the BV shim faces concave too. like .1mm deep or so.

Edit again:
Went back to the Stock OEM BV just to see what it was like but as expected it was not too good. But it helped me understand what was needed. Far too soft the feeble BV made the fork compress too far and caused too much launching in some cases, given more rebound damping on the clickers to cure it made the fork too taut and irresponsive to rider input. Took a while to realize it. Then tried the stack above altered to plan, that is:
valve face
24
24
24
12
24
22
20
18
16
14
12
10 .3
18 .2
BV post
And it was a lot better than the oem stack.
Best combination with this weak MV at 0.7 mm float so far though was with the first used with it. I thought it was too stiff but it was the other way around. Should not have removed any shims at all but instead added.
Alternatively beef up the MV again, which generally felt good, but I'm afraid that the harsh topping out would return on mild washboard bumps. There is only so much pressure in the fork.
But one thing at a time. My plan is to not stick to any fixed plan but to constantly reassess and react accordingly.
The MV is like an extremely small but very aggressive dog. It is attacking anything that moves but it can do very little harm, if any, or even annoy. A big dog would do the job better but it would need to be more tolerant. In other words; back to a thicker MV to make it more effective and give it more float to make it engage more gently.

And yet another edit;

As you now know I tried a weaker stack for the MV and a smaller diameter pivot using a wire ring on the tap. It really rewarded slowness.

It can now flex 2.5 mm before it hits the stop. That could be shim brutality.

Click to expand...

It was, some shims had to be replaced since they deformed (pringle crisp) in very little time. The edge of the 18 mm shim in the MV frequently engaged the 2 mm cut down in both cases, I know because the blueing put on the shim surface wore off where it engaged. It must have saved them and with the wire ring on the tap this 2 mm flex gap increased to 2.5 mm, or even 2.6, which, as it appears, was too much flexing for them to take.
The conclusion is that the 2mm flex gap should be maintained at 2mm to limit the stack flex at full storm or the shims are going to get damaged.
The idea of using 24's only backed with a curved washer in the MV seems even sweeter now. If only I could find any suitable material to make the curved washer...


MV is now at 1.1mm float, back to 2 mm flex limit @ dia 16 mm (by removing the wire ring) and the following stack.
24 0.11 (KYB shim)
2x24 0.1
22 0.1
20 0.1
18 0.1
And I could not feel any difference between 0 to 4 mm of spring preload so now I left it at 3 mm. I fear that the fork will get bouncy riding very steep uphill if there is too much preload but I dont know really.
BV is still
24
24
24
12
24
22
20
18
16
14
12
10 .3
18 .2
Compression adjuster opened 12 clicks. 13 clicks made it harsh and threw you in rocky stuff. What a difference a click makes...
Rebound adjusters opened 14 clicks.
Funny that making compression damping too soft made riding rocks and roots harsher. Now with more compression shims the fork is soo smooth.

And yet another edit;
MV is now at 1 mm float, 2 mm flex limit @ dia 16 mm. Replaced the 0.11 face shim with a 0.1 shim and added another 0.1 mm 24 dia shim. This is actually almost the MV I started with!
The Kayaba 0.11 shim used as a face shim in the MV doughnutted almost as easily as the original 0.1 shim. Not that it had gone very far.
4x24 0.1
22 0.1
20 0.1
18 0.1
(Next time maybe a 0.15 as the face shim in the MV will cure the doughnutting. Then with some more backing shims to support the 0.15 better. Or the curved washer.)

BV is slightly softened since the MV is slightly streghtened:
24
24
24
12
(This is where a 24 used to be, I pulled it)
22
20
18
16
14
12
10 .3
18 .2
It's actually like the oem BV stack with a 24 face shim added.
Compression adjuster opened 12 clicks.
Rebound adjusters opened 13/14 clicks.
And this time new oil! Level = 130 mm. No, I did not experiment with the oil level at all.
Q8 Fork Oil Light 5, 21cSt @ 40degC, V.I.=219, , same as before.

It works quite well now so I see no reason to open the fork legs again for a while.

I start to think that there are two separate reasons the MV shims are getting damaged:
The dughnut damage is from the port edges on rebound. This damage is limited to the MV face shim only. This takes a long time to develop. Should be possible to suppress by using a heavier face shim.
The pringle crisp damage from being allowed to flex too far on compression. This can happen to any shim in the MV stack, it did, even to one in between two undamaged. It happened within a just a few hours of riding. Seems like the backing, shims and flex limit, is important to stop this from happening.

regards

I think I'll bump it this time to see if anyone would like to comment.