Here is an very interesting thread from thumpertalk,
fork modification from Dave Johnson "Phase 4" actually it´s for KYB´s but his ideas should work on WP too?
http://www.thumpertalk.com/forum/showth ... p?t=431575 &
http://s22.photobucket.com/albums/b341/davetj123/
And here it is, the KYB PHASE 4 Fork - a home grown build-up that is the cumulative result from just about everyone that has ever posted a question or an answer on the ThumperTalk suspension forum. All that stuff that keeps you thinking and wondering and, well, humble.
It is an old fork made new. Possibly, an old fork made new to be better than anything out there, new or old. It’s not the likes of a hot rod or a big bore kit, but more along the lines of throwing out the old clunky carburetor and bolting on the latest in electronic fuel injection – perfect combustion regardless of terrain, speed or the need of the rider.
It is that good.
It is quite possibly the best fork that any of you will ever ride on. It’s so good that it requires you to re-learn how to ride, to look at a pothole, root or a g-out and say, “So what”. For me, it has removed the fear and brought back the fun in riding. Riding the tracks, the woods, fetching firewood. It works.
I have gone through more fork designs and rounds of testing in my life than Travis Pastrana has done back flips, and this one tops them all. Yes, the KYB Isolated Damping Fork (IDF) was a big step forward, but this one just nails it and confirms the feel of what riding a bike is all about. Have I made my point?
Onward! :applause:
Why PHASE 4?
There are four design aspects that make this fork work, responsive (rapid) hydraulic damping, cartridge backfill, bottoming and ulta high speed blow-off.
Now, some of those can’t exist without one working with the other, making this a very integrated and dependent design. Here’s why.
We have read over and over again all the various complaints that TT users have with their forks. Oddly enough, users will post concerns about a fork that feels stiff but also seems to blow-through or bottom too frequently and in worse case, is soft but seems to push in the corners.
The simplest answer, without providing a solution, is that the problem is one of too much or too little damping. Not enough when you need it, and too much when you don’t. The tuner’s challenge then becomes the process of removing and adding shims in order to flatten and reshape the damping curve but at a cost of compromising performance elsewhere.
Here’s what’s happening. In the first chart the low speed damping does not climb fast enough. This is common with mid-valves that have too much float. For these movements, the rider may end up getting an improper balance between spring and oil resistance, which I often refer to as “riding the spring”. During ultra high-speed movements, the base and mid-valve stacks are as wide open as they can get, but they are not able to vent the volume of fluid in such a short amount of time. The reason? Shims are only capable of progressing at a linear or greater than linear rate. In other words, you can never expect a shim to lift to some degree, then ask it to get soft. Once the climb starts upwards, it is never going to flatten or drop off while velocities build.
The real trick is getting a shim stack to behave on both ends of the spectrum. To have ideal low, mid, high and ultra high-speed performance.
Now, while we are on this subject, there is another matter that I call “hydraulic crossover”. It is the process or measurement of when one damping circuit reaches a limit or boundary and another damping circuit comes into play.
For example, most of us know that when you turn a clicker screw you are bypassing the shim-stack. In most cases, the by-pass circuit is so small that the only effect that the clicker will have is towards the bottom of the damping curve. The reason is that the port or hole size of the by-pass can only accommodate a given amount of fluid before it reaches a maximum flow regardless of how much pressure is put on it. This is called “hydro-dynamic lock”.
This means that at some point, the by-pass circuit locks, and the shims on the piston need to lift to accommodate the fluid flows. However, the timing of this “cross-over” is critical in that if the bleed circuit is maximized before the shim stack can lift, you’re left with a hydraulic or damping gap. Without getting too far into this, the trick is to have a seamless and smooth transition in force (resistance) as velocities build.
With that in mind, let’s get back to taking a closer look at the PHASE 4.
The first matter at hand was to be able to build-up a rod stem that could accommodate the works. A blow-off circuit, a configurable mid-valve stack, a limiting device for the mid-valve stack and the rebound stack, and do so with a design that can use both the earlier one piece piston and the later two piece pistons.
This meant laying out all the components and machining a new stem to meet the new spec.
And here are what the stems look like fresh off the CNC. These are made from 303 stainless but I can also get them made from titanium ($$).
The next step was to produce the base assembly but this was carried over from the same design that I used with the IDF design. No real change except some additional considerations for load and spacing.
The chart on the left shows the loads that are applied on the blow-off springs via the shim pre-load rings (not shown).
Here are the final pieces.
The next step was to build a cartridge back fill device without losing the option of using the RSP bottoming cones (more on these later).
This meant that fluid would have to flow in and behind the mid-valve as compression cycles occurred but close and lock the fluid in as rebound cycles occurred – your basic check valve.
However, it’s a tight space and the design would have to be rapid enough to allow the valve to open and shut a few hundred or thousand times a minute, and the flows would have to be generous enough to meet the needs, so to speak.
The fix was to add two sets of three ports into the RSP cone, three on each side that go from the top and outside of the cartridge, and curve and flow downward. BTW - any bubbles that may build up on top of the fluid are well over 2 to 3 inches above the intake ports of the valve.
Then a new strike plate would need to be created to accommodate the flows coming from the RSP cone, and also hold and manage the new check plate and spring.
And here is what they look like assembled onto the cartridge.
AND…this is what the complete assemblies (mid, rebound, blow-off and back-fills) look like before they are put into the cartridges.
The last item was also a carry over from some of the IDF work and which is obviously part of the PHASE 4 fork. This is, the Double Bottoming System (DBS). This is the integration of a hydraulic end-of-stroke oil lock that also incorporates the factory bumper bottoming system by engaging a fixed amount of the bumper stop before the bottom of the hydraulic stop is reached. This is done by shaping the spring guide and lock nut to bring the top of the RSP cone in contact with the bumper stop. For most of the forks I have built up the engagement is set to 3mm.
Here is a photo to show how these assemblies came together.
So that’s it.
Beyond this is the need for others to build up the same fork, or use components of this design with other designs. For example, if a tuner wanted to swap out the existing factory cartridge valves and offer their customers the additional advantages of the bottoming system they could simply use a kit as such.
In other words, the backfill and DBS option should allow the professional tuner or DIY the ability to expand and build out their fork line without having to go to such extremes as adding or building in all the blow-off circuits.
However, if it were desired, an entire kit as such could also be acquired. This photo shows all the parts used to completely build-up a pair of PHASE 4 forks.
Now, in the spirit of ThumperTalk and the fact that all of this was really derived from the help of others, this fork design is free to anyone who wishes to built it except those that wish to build them for profit. If you have the machining and mechanical assembly skills, I have no problem with providing all the drawings and specs that one would need to go at it. Consider it the equivalent of an open source code. Besides, the more the merrier.
However, I can already tell you that if you had to go out and purchase all the required springs, the RSP cones, the material and machine labor, you’re looking at a hefty price tag. I built three prototypes and each pair was about $600. However, if I purchase and have stuff made in quantity the price comes down significantly. I have yet to figure this out but if there’s enough interest I’ll be more than happy to make it happen.
Lastly, I have mentioned that I am not in the suspension business per say, in that I don’t do the work as so many other readily available shops do. However, this one is a bit of exception simply since it is such an amazing fork. If you have the money and the need, but not the skill or the time to deal with it, I can take in about 10 to 15 forks over the next month. Again, I’ll have to work over a price but I think it can be done for about $375 for the pair. Additionally, this fork has an endless array of configurations for shim stacks and blow-off rates so there is really no end as to how you can tune it and what you can use it for.
Lastly, I guess it is intuitive that for those that always dreamed of the perfect woods and MX fork, this is it.
Now, I own and use one of the three prototypes. The other two have gone out to two other TT members, one of which also has a set of KYB TCs to make a comparison to. Both are advanced and worthy riders and hopefully will have the time to chime in and provide some additional opinions other than my hype.
Let me know if you have any questions.
SPECIFICATIONS
GENERAL
Name: KYB PHASE 4
Type: Inverted Dual Configuration – telescopic KYB – open cartridge – 46 and 48mm
Application: Motocross, Supercross, Woods, Desert
Travel: 11.5 - 292mm
Fluid: KAYABA FR01 Racing Suspension Fluid
Fluid Capacity: 596cc minimum
HYDRAULIC DAMPING
MID-VALVE
Stem: 43mm stem – 303 stainless or titanium– standard porting
Piston: 2 or 4 port 32mm KYB – standard or polished porting
Stack: Configurable up to 14 shims – single or multi-staged
Lift: 24mm limit plate with adjustable shim stop
Blow off: Adjustable compression spring. Rate = 318inlbs/56N
Blow off shims: 0 to 6 – .5mm (.020”) increments
Maximum Blow off rate: 37.77lbs/168N
BASE
Stem: 37.8mm stem – modified KYB base - aluminum
Piston: 4 port 25mm KYB – standard or polished porting
Blow-off shims: 0 to 6 – .5mm (.020”) increments
Stack: Configurable up to 14 shims – single or multi-staged
Lift: 24mm limit plate with adjustable shim stop
Blow off: Adjustable compression spring. Rate = 318inlbs/56N
Blow off shims: 0 to 6 – .5mm (.020”) increments
Maximum Blow off rate: 37.77lbs/168N
REBOUND
Piston: 2 or 4 port 32mm KYB – standard or polished porting
Stack: Configurable up to 14 shims – single or multi-stage
CARTRIDGE VALVING
Type: Multi-port spring loaded one-way check plate
Back Fill: Double sided 6 port – rebound lockout with .33inlbs/.06N clamp spring
Strike Plate: 6 port 303 stainless or titanium
SPRING
Accommodates all standard Kayaba and aftermarket spring sets
Air/Oil: Minimum/Maximum Fluid Level: 130mm/80mm
Spring Pre-load: 10mm preset – adjustable with 2.2mm ring plates
BOTTOMING CONTROL
End of stroke: Double Bottoming System (DBS) with modified RSP hydraulic lock 866 taper plus rubber damper - 3mm engagement
SETTINGS
Base Compression: Standard KYB needle by-pass – 14 settings
Rebound: Standard KYB needle by-pass – 14 settings
