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Old 12-26-2006, 04:29 PM   #1
Zerodog OP
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Location: SLC, UT
Oddometer: 1,233
Cool2 Check out my stacks---Zerodog's fork mods

Here is the mods I came up with for my 03 640A. The problems it had were, a harsh ride on dirtroad washboard without subtanks and very open compression clickers. But even though it was too harsh on small stuff the fork was very divey on downhills and braking. The plan was a beefed midvalve and lighter 2 stage basevalve. The idea was to keep it high in the stroke but suck up small bumps like gravel and washboard easy.

On this list I use 1 instead of .1 and 1.5 instead of .15 for the thickness
This is for use in a graph I am working on. If I get it worked out it will be cool to help visualize valve stacks.

Stock 640 Adventure Fork

Base Valve
6 24 1
2 20 1
2 18 1
16 1.5
14 1.5
10 3
18 2.5

Midvalve
4 24 1
22 1
20 1
18 1

.7 stack
1.8 float

Rebound
5 Delta24 1
20 1
18 1
16 1
14 1
10 3
16 3

100mm oil height ?wt from previous owner



Mods 12/24/06

Base Valve

2 24 1
12 1
24 1
22 1
20 1
18 1
16 1
14 1
12 1
10 3

Midvalve
3 24 1
22 1
18 1
14 1
10 1
12 1
14 1
20 1.5
2 10 2

1.45stack
1.13float

Rebound
4 Delta24 1
20 1
18 1
16 1
14 1.5
10 3
16 3

100mm Oil height 5wt oil


So what did it do?

On my initial test riding around town. (No Offroad yet) It seems to be better on square edge bumps like manhole covers and pot holes. Before these were jarring to say the least. The subtanks made this kind of hit better but then it is too soft for me on the street. With the heavier midvalve it does ride higher in the stroke. There is a lot less brake dive. I have to really stab the brake to get it to really dive hard. But it still has 4-5 inches left. With the old valving I could almost bottom it. On dips between streets and into parking lots the fork Gs out a lot less too. I went to a school that has a series of speed bumps. It felt good but nothing surprising. I was mostly impressed with my curb test. (Driving straight into a 6inch curb like it isn't there.) First 10mph. The fork moves and sucks it up nicely. No harshness. 20 mph. Even better. I didn't even lean back. It just sucked it up. I think the curb would have popped my tire with my old setup. It just feels very progressive. All testing today was done with the tanks off. I can't wait to get it on dirt. This weekend will be the test. Desert Whoops here I come!

Zerodog screwed with this post 12-26-2006 at 05:01 PM
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Old 12-26-2006, 05:18 PM   #2
creeper
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Quote:
Originally Posted by Zerodog
Here is the mods I came up with for my 03 640A. The problems it had were, a harsh ride on dirtroad washboard without subtanks and very open compression clickers. But even though it was too harsh on small stuff the fork was very divey on downhills and braking. The plan was a beefed midvalve and lighter 2 stage basevalve. The idea was to keep it high in the stroke but suck up small bumps like gravel and washboard easy.

On this list I use 1 instead of .1 and 1.5 instead of .15 for the thickness
This is for use in a graph I am working on. If I get it worked out it will be cool to help visualize valve stacks.

Stock 640 Adventure Fork

Base Valve
6 24 1
2 20 1
2 18 1
16 1.5
14 1.5
10 3
18 2.5

Midvalve
4 24 1
22 1
20 1
18 1

.7 stack
1.8 float

Rebound
5 Delta24 1
20 1
18 1
16 1
14 1
10 3
16 3

100mm oil height ?wt from previous owner



Mods 12/24/06

Base Valve

2 24 1
12 1
24 1
22 1
20 1
18 1
16 1
14 1
12 1
10 3

Midvalve
3 24 1
22 1
18 1
14 1
10 1
12 1
14 1
20 1.5
2 10 2

1.45stack
1.13float

Rebound
4 Delta24 1
20 1
18 1
16 1
14 1.5
10 3
16 3

100mm Oil height 5wt oil


So what did it do?

On my initial test riding around town. (No Offroad yet) It seems to be better on square edge bumps like manhole covers and pot holes. Before these were jarring to say the least. The subtanks made this kind of hit better but then it is too soft for me on the street. With the heavier midvalve it does ride higher in the stroke. There is a lot less brake dive. I have to really stab the brake to get it to really dive hard. But it still has 4-5 inches left. With the old valving I could almost bottom it. On dips between streets and into parking lots the fork Gs out a lot less too. I went to a school that has a series of speed bumps. It felt good but nothing surprising. I was mostly impressed with my curb test. (Driving straight into a 6inch curb like it isn't there.) First 10mph. The fork moves and sucks it up nicely. No harshness. 20 mph. Even better. I didn't even lean back. It just sucked it up. I think the curb would have popped my tire with my old setup. It just feels very progressive. All testing today was done with the tanks off. I can't wait to get it on dirt. This weekend will be the test. Desert Whoops here I come!
Interesting stuff Rob... looking forward to a more complete review of your impressions, when you get the chance.

Something that might be of value to others is your weight, approximate riding ability level or terrain/speeds you encounter, fork spring weight and approximate shock set-up... as a point of reference.

That "curb test" thing you speak of... you must video tape that.

C
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Old 12-26-2006, 06:53 PM   #3
Zerodog OP
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I will try to video the curb test this week. I will do 10, 20, 30+mphshots. This is winter urban suspension testing at its best.

Other info as requested by the Creeper man:

Rider weight 190 Ability-advanced trail rider...at least on a real dirtbike.
Terrain mostly ridden. (pretty much the full range of what a 640 could encounter) loaded, unloaded and even 2 up offroad. Roads, desert dirt roads and trails. Then in the summer, mountain dirtroads, jeep trails, and singletrack.

Basic fork setup
front springs 5.0s
rear 8.0
Fork clickers
Rebound 6 out from fully closed
compression 7 from fully open...I think?

Basic shock setup
Revalved shock by Trail Trick and me.....soon to get more work by me.
Around 110mm sag
7 compression... needs some more low speed or maybe some more preload on the spring.
8 rebound......needs some more high speed for big g outs when loaded down(with my GF on the bike)
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Old 12-26-2006, 07:02 PM   #4
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Groovy Robski...

That should give everyone a base line from which to work something out for themselves.
Or, if they don't know which end of a wrench is which don't feel confident doing the work themselves, they can send their forks to you I bet... and for a reasonable fee, you'll hook them up yes?

Don't forget them crash curb shots!
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Old 12-27-2006, 12:49 AM   #5
bmwktmbill
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Zerodog and all,
Let me be one of the first to thank you for sharing your work. You are the only suspension tuner that I know of who is this open with potential customers. We all owe you our respect and we are in your debt. I hope this forum can continue with the same spirit of openness.
After all, we aren't racers trying to get to the finish line first.
We are all interested in making our motorcycles ride more safely and comfortably.

For those who don't know about the history of suspension tuning, let me say that it is mostly closely guarded secrets, snake oil and bullshit.
There is a guru factor.
Often large sums of money trade hands and the results for the riders are mediocre at best.

My '02 Adventure has even more antique suspension than your '03.
I have no midvalve. It consists of a checkplate comprised of 4x24x.1 shims. The float was similar to your stock setup.

I did run a modded basevalve all summer with two 24mm shims on top. There was no problem with durability and it makes you wonder why KTM chose such heavy valving for the stock setups. The basevalve changes were a good first step for me but no substitute for the complete re-valving work you are doing, with testing and reported results.

Don't get going too fast with that new setup. You have to stay healthy.
You are the man.
BTW, +1 on lightening the rebound stack, it might need more??
Bill.
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'02 KTM 640 Adventure-lowered
"On the road there are no special cases."
Cormack McCarthy-The Crossing

The faster it goes the faster it breaks.
And high performance=high maintenance.
Bill Shockley
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Old 12-27-2006, 07:01 AM   #6
Zerodog OP
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Thanks Bill! The midvalve/ checkplate that was on mine stock isn't a whole lot different then what you are running now. You can build up your midvalve to be the same as what I am running. I filled up full with gas this morning and it still stays up in the stroke. Watching my headlights dip a lot less when I shift let me know that it is moving a lot less under this kind of weight transfer. So I think the midvalve is the answer to the divey mushy action of the 640a. The 640 is so heavy up front that controlling weight transfer is key to making it ride better. I did lighten the rebound on the lowspeed side but I also made it stiffer on the high speed section by adding the thicker 14x1.5mm shim. This helps with the bigger fork motions. This is what I want to do to the shock too. Build up the smaller diameter shims so it helps resist this kind of bobbing on large g outs. I am not sure why manufacters choose such heavy stacks for basevalves. Most guys don't need it at all. But I think to some degree it makes up for heavy riders with the wrong springs. I think the main thing is they try to come up with something that is Ok all around. If they pick any one way to set up a suspension someone somewhere will hate it.
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Old 12-27-2006, 11:29 PM   #7
bmwktmbill
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Rob,
I am with you on the "all rounder" approach.
The need for that kind of thinking would cause most tuners throw up their hands and start talking smack.

My ride weight can easily vary by 120 lbs with travel gear and gas.
I shudder to think of ever adding a passenger plus gear.
Keep testing and thanks.
Bill.
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'02 KTM 640 Adventure-lowered
"On the road there are no special cases."
Cormack McCarthy-The Crossing

The faster it goes the faster it breaks.
And high performance=high maintenance.
Bill Shockley
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Old 12-28-2006, 09:23 AM   #8
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hey rob i had bel ray 7.5 in the forks. that with the .50's was a little harsh on road, but it worked for me off.
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Old 12-28-2006, 11:18 AM   #9
Zerodog OP
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2spot, my current setup rides like a magic carpet on the road now. Plus I lost the horrible brake dive.
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Old 12-28-2006, 02:03 PM   #10
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yeah i bet its a whole different bike. keep us informed when you get it off road.
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Old 01-01-2007, 06:33 PM   #11
Zerodog OP
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Thumb

Yesterday I went for a ride at an OHV area near Salt Lake. It is all high desert hills and mountains and usually snow free. It is a very rocky area and is a good test for the new set up. Anyway there was a lot of snow. The 606s are not the ideal snow tire and a 400lb enduro is not the ideal snow bike. So it was slow going. But my friend and I went out for a ride anyway. For some reason it must have been inversion or pollution or whatever, the higher we got the less snow there was. There were entire hillsides that were snow free. So I got to test the bike on some rocky steep hillclimbs and some rough trails. I wish I brought my camera for some shots.
It is amazing the difference the midvalve and the lightened basevalve has made for the way the bike handles and absorbs bumps. The feeling is much more progressive and controlled. I was running over everything on purpose and it was smooth sailing. Instead of riding over rock bands I was jumping over them without worrying what I was landing in. The most impressive part was the downhills. The bike tracked where I wanted it to go and didn't deflect off rocks and try to twist the bars out of my hands. This was one of my biggest problems with the stock suspension. Even with the heavy 5.0 springs it was a divey MOFO on steep hills. On the same type of hills I would have been dragging a foot and riding scared but with the new set up I was able to stand up and ride down like my dirtbike. All in all it was a pretty fun ride.
Sorry Creeper, no curb test videos this weekend.
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Old 01-01-2007, 07:47 PM   #12
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Quote:
Originally Posted by Zerodog
Sorry Creeper, no curb test videos this weekend.
Bummer. And I was sooooo hoping for some nice 100 mph curb hits too.

Soon as it warms up a bit more around here, I'll blow my forks apart and see what kind of stack Dick Dyer set me up with... my fork action sounds very similar to your fork action, but a tad stiffer with the .52s.
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Old 01-02-2007, 12:35 AM   #13
bmwktmbill
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Zerodog,
Great news.
Kudos for "Z stack number 1".
The first published and tested complete revalve for the LC4 640.
Fitting that it is here on Adventure Rider Thumpers forum.
Congratulations and thanks.
Bill.
__________________
'02 KTM 640 Adventure-lowered
"On the road there are no special cases."
Cormack McCarthy-The Crossing

The faster it goes the faster it breaks.
And high performance=high maintenance.
Bill Shockley
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Old 02-16-2007, 12:19 PM   #14
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So I tried a re-spring and revalve yesterday on my '02 with WP4860's and ran into some trouble because I'm completely new to suspension work.

First off, for anyone who's interested here're the stacks that are on the stock '02 forks:

Base: (6mm ID)
6 x 24 x .1
2 x 22 x .1
2 x 20 x .1
2 x 18 x .1
1 x 16 x .15
1 x 14 x .15
1 x 11 x .2
1 x 18 x .25

Midvalve: (8mm ID)
4 x 24 x .1
about 1.2mm float

Rebound: (6mm ID)
5 x 24delta x .1
1 x 20 x .1
1 x 18 x .1
1 x 16 x .1
1 x 14 x .1
1 x 10 x .3
1 x 16 x .25


I knew what shims where already on the bike from the parts fiche, but didn't know how many of each. I ordered a bunch of extra shims, but that was no big deal. What was a big deal was that I ordered 6mm id shims for the midvalve instead of 8mm Shoulda paid more attention to the fiche.
Some of the shims weren't available, so I made some substitutes: 2x14x.1 for 1x14x.15 in the rebound stack, and 3x10x.1 for 1x10x.3 in the base stack. The 10mm shims in the base stack rest against the body of the base, so the change in flex doesn't matter.

I left the midvalve alone, but had a big question about it:

How do you set the float? Is it with little spacers between the rebound tap and the cartridge piston? Pic . The stack+float value is 1.6mm for my forks, 2.5mm for the stock '03 valve 2.58mm for the Zerodog valve.

Or, if I am stuck with the stack+float distance, what should I do to the stack? I figure a general beefing up of the stack would be a good start. How important is the float? I was going to add a washer to the midvalve, but it would have taken up nearly all the float, so I left it out.


Zerodog, thanks so much for sharing what you found. It's a great head start for us tinkerers.

I'll share the results when I get some... I haven't even ridden the bike yet!
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Old 02-16-2007, 05:58 PM   #15
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Man bummer that you ordered a bunch of shims without checking. You mostly remove shims from the basevalve for my mod. MX tech has a great selection of shims too. The midvalve float is key to making it work correctly. The float is the distance the shims can open riding on the spring before they start to deflect. To measure the float remove the spring and measure the gap that is between the shims sitting on the rebound tap and the piston. Or remove all the shims measure the gap and then measure your shims. The difference is your float. My float is 1.13 on my bike. Yours is probably around 1.8 stock. The numbers you are listing are not right. Washers WILL NOT WORK to take up space to lower the float. You need to use real deal shims so they can flex.
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