Harold Bawlzangya Racing

KYB twin cartridge forks revalve for woods riding

It has been a while since I’ve added anything to this page or made an update.  I’m finally getting around to making some over-due changes.

I’ve removed the Restacker graphs and Excel charts with the various re-valves I’ve made over the years.  I did this for two reasons – I needed to free up some space and it wasn’t very helpful showing all the combinations I tried and didn’t like.

Some things I’ve learned . . .

I can’t tell the difference in making a single shim change from one re-valve to another.  Especially when it is weeks or months between rides.  I have lost count of the number of re-valves I’ve made where the only difference was a single shim.  Looking back on it, that was all wasted effort, time and money.

I’ve made the most progress on zeroing in on the right shim combination when I’ve done two things:  Make drastic changes and compare one re-valve to another as quickly as possible.  So instead of increasing the float .1mm, I would try .3mm.  Or instead of removing 1 shim on the mid-valve, I would remove 3.  These drastic changes removed any doubt on the impact of that change.  It then became easy to say that adding float made the forks better/worse.  Or that softening the mid-valve made the forks better/worse.

Comparing re-valves quickly while the feel was still fresh in my mind was a little more challenging.  If I’m lucky, I might ride once a month.  But it is more common for several months to pass between rides.  That makes it nearly impossible to remember what the forks felt like with the last re-valve.  My solution was to create a test course of obstacles in my back yard.  I used big rocks (10-12″), bricks, logs and some old 6″x6″ landscape timbers to test the type of conditions I would encounter in the woods.  This allowed be to hit these obstacles a number of times, pull the forks apart and make a change and hit them again within 45 minutes.  The one thing I couldn’t test with this set-up was how the forks felt at higher speeds.

Float – a little or a lot?  The one thing that I consistently read about re-valving forks for the woods was to increase the float.  Therefore most of my re-valves used higher than stock float amounts.  No matter what I did, I just couldn’t get the kind of feel I was looking for.  There is no doubt that a fork with a large float will absorb the trail trash very well.  But to me the feel of the fork was “mushy” and disconnected from what was happening.  There were also circumstances where the forks became harsh.

One day I finally decided to try a new approach of  a very tight (by off-road standards) float combined with a very soft (by MX standards) mid-valve.  This was the combination I had been looking for!  In retrospect, it makes sense why those large float re-valves just never felt right.  With a high float, you need a reasonably stiff mid-valve or base-valve to provide any level of bottoming resistance.  So when the float “runs out”, the stiff mid-valve comes into play and things get harsh.

This low float/soft mid-valve combination gives enough feedback to know what is happening, but I’ve never experienced any deflection or harshness.  Having a soft mid-valve working all the time provides a more consistent ride.  I think the only drawback is that the mid-valve shims may wear faster, but time will tell on that.

The next time I pull the forks apart I will post those stacks.

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As I learned from my other revalve, I won’t be getting it right on the first try.  After just 2 revalves on these TC forks, I was quickly missing how easy and clean it was to work on the OC forks.  So I used some extra parts from the OC forks to making bleeding and rebuilding the TC forks easier, cleaner and with wasting less fork fluid.

I used THIS INFORMATION  / SMART PERFORMANCE INC. procedure to bleed the cartridges.

The first area I tried to improve for myself was getting all the air removed from behind the mid-valve when filling up the cartridge.  The procedure has you install the cartridge rod first, fill up the cartridge and then bleed off the air that was trapped under the mid-valve.  I was probably doing something wrong, but it felt that I had to work a lot longer to get all the air out.  And even then I though I could still hear air bubbles when cycling the cartridge rod.

My solution was to extend the cartridge rod so I could fill the cartridge first and then drop the mid-valve into the oil – similar to how you rotate and drop the base-valve into the cartridge to expel the air.  Again I turned to some spare parts from a set of KYB OC forks.  In the below picture I’ve already cut down the cartridge rod.

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Next step was to screw the mid-valve post on the threaded end and insert the dampening rod into the other end.

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This next step would normally be done inside the cartridge, but it is easier to see what I’m trying to accomplish without it.  I’m just sliding the actual cartridge rod onto this ‘jig’ . . .

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When the two pieces are together, I essentially have one long cartridge rod.  The purpose of this should become clearer in the next set of pictures.

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So now I can secure the end of the jig into a vice.

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And then slide the cartridge over it.

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The next step is to slide the jig and cartridge rod together so the mid-valve extends out of the cartridge.

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So now I can fill up the cartridge (not all the way to the top) with fork oil and get oil behind the mid-valve.  The next steps just involve dropping the mid-valve down into the cartridge.  Or put another way, extending the cartridge rod out of the cartridge.

To do that, I’ve been using a dampening rod to push the mid-valve down while I pull up on the cartridge rod.

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As the mid-valve drops below the oil level, I rotate the cartridge around and tap it to release any air bubbles that may be trapped in the ports of the piston.

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As you push the mid-valve down/slide the cartridge rod out, eventually the rod of the jig will come out, exposing the cartridge rod.  At that point you can grab it and pull it out all the way.

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Then it is on to the bleeding process.  This procedure is messy and can potentially waste a lot of fork fluid.  Here is what I’ve put together to contain the expelled fluid so I can re-use it.

I’m not sure what the actual name of this part is from the KYB OC forks, but it is a ‘nut’ that screws on one end of the cartridge rod, opposite of the basevalve.

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I then aluminum soldered it to a scrap piece of aluminum plate.  I drilled a drain hole at the bottom so fork oil wouldn’t get trapped.

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Then I bolted it to a bottom of a bucket.

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Just screw the cartridge rod into the fitting and begin the bleeding process . . .

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The next few pictures show the oil that I had been wasting before.

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I’ll then pour the fluid through a coffee filter into a clean container to be used for filling the outer cartridge oil level.  I’m not trying to clean dirty/old oil, just trying to get any debris that may have gotten into fresh fork oil.

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I’ve done several revalves and will be going back and filling in those details.

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12.18.11 Update

Went for a TEST RIDE with the below settings and it wasn’t completely terrible.  The forks weren’t compliance enough of small chop and when traveling around 5-10 mph, the forks didn’t seem to move when going over rocks or ruts.  Instead the front wheel just seemed to follow over the obstacle.  I think I’ll try opening up the float a little and further soften the MV.

(chart removed)

 

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12.21.11 Update

I’ll be testing the below shim stacks on my next ride.  As I was making these changes, I had a thought about my oil volume.  Since my forks are roughly 5% shorter than factory, I should be using 5% less oil for any given setting.  Last ride I used 300 cc’s of oil and had good bottoming resistance.  So this time I’ll try 285 cc’s and see how compliance and bottoming is impacted.  I realize I’m making a number of changes at once, but I’ve done some additional research and have come across some information that gives me some additional confidence to make multiple changes at once.

(chart removed)

 

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I went for a ride on 1.1.12 with this set-up and it worked well. Much better on washboard type bumps than the prior set-up.  Only bottomed once, but wasn’t totally surprised by that since I tested out a low oil level.  I think the extra .05mm of float and softer mid valve played the biggest role in the improvements.

(chart removed)

 

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On the 1.7.12 ride, I tested the above set-up but with .3mm of float.  It was slightly better on small washboard bumps, but was too soft everywhere else for my taste.  So I’m considering the 1.1.12 stack my ideal conventional set-up.

I’ve been following a couple of recent posts (this one and that one) on Thumpertalk related to the SPI DDT set-up for offroad riding and thought I’d try that set-up again.  First thing I did was set-up this spreadsheet so I could calculate the amount of shims I would need to coil bind the small DDT spring to limit the blow-off.  I added .4mm of shims below the collar and with the below shimstack, my blow-off limit was reduced to .62mm.

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This is what the mid-valve looks like in Restackor.

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Below are all three stacks I’m using.

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I didn’t have the right OD shims to put under the collar, so I ground a few larger shims down.  A little difficult to see, but there are .4mm worth of shims under the 7.3mm collar.

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Small DDT spring.

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Larger DDT spring

The pressure from the springs makes it impractical to install the shims and then the piston.  The easiest way to install the shims is to build the stack with the piston turned upside down.

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While holding the springs in place insert the rebound holder stem into the piston.

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Once the piston is on, hold it in place with light pressure from locking vice grips. Then you can build the rebound stack as usual.

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It will be another week before I have a chance to ride this set-up.

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2.9.12 Update

I recently got a set of 2011 KX450F forks to work with.  I was able to go on THIS RIDE to test the 2011 forks against the 2007’s with the DDT set-up.  With the 2011 forks, I didn’t make too many changes to the base valve – just pulled a couple of face shims and then clamped it on a 14mm shim.  The mid-valve received the most changes, I didn’t keep much of the factory stack.  Instead I mirrored the midvalve stack from the CRF450 and made some other changes to be more woods friendly.  This is what those stacks looked like:

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After being able to compare the 2 forks back-to-back, I liked the 2011 forks enough that it is time to start shortening them to fit the 2-stroke.

The .48 springs in the 2011 forks are much heavier than what I’ve used on the KX450F or the KX125 forks in the past, but the forks felt so good that I don’t want to change much at all.  So instead of using shorter springs, I’m keeping the factory springs and will be approaching the shortening a little differently.  I’ll be moving up the spring perches to lower the forks.

The first step involves cutting off the spring perch stop.  The factory stop is crimped so it cannot slide down over the circlip. Once the stop is cut, it can be pried open, allowing it to slide off the circlip.

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I ordered replacement stops and clips from Suspension Direct.  They shipped same day.  I received these a few days later.

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Since I didn’t have any way to cut a new groove, I had a local machine shop do it.  I’ll be lowering these forks 13mm, that will give me 5mm above the triple clamp as a starting point.

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Next step will be to cut the cartridge rods.  The rods from the ’11 forks are a little different.  With the ’07 rods, I was able to shorten then on the end the rebound adjuster bolt threads onto. But with the ’11 rods, this section was machined narrower than the diameter of the threads.  So this end won’t work.

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I will have to work from the end that the rebound piston holder threads onto.

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The set-up I’m using on the table saw.

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The first operation is to reduce the diameter of the rod a bit.

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Ugly looking. . .

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Looks better now.

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Cutting the rod, make sure to thread the tap on first to clean up the threads that are cut.

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Both rods cut down.  The one on the top has the diameter reduced at the very end.  That is necessary to get the rod to seat fully in the rebound piston holder.

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Everything cleaned up with the rebound piston holders tightened down with red loctite.

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The new style midvalve on the left and the older style on the right.

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Got the shims all cleaned, measured and laid out in order.

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This first shim limits how much the stack can deflect into the new style midvalve.  I believe the MX set-ups are using two .25 shims to limit deflection.

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The next three shims flex instead of the 2 x 17.30 shims that are usually used in the old style mid-valve.  The KX450F set-up used 2 x 20.11 shims.  My first time riding these new forks I used a 20.11 and a 17.11 taken from the CRF set-ups.  The three shims I’m trying now fall in between those two configurations.

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The next set of shims controls the amount of traditional float provided. I’m using ~.20mm of float again.  With the old style spring loaded mid-valve, I used feeler gauges to check the float.  But on the new style I was having a difficult time using a feeling gauge, so I measured the thickness of the shim stack vs. the working height under the piston.

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And then there is the traditional stack that is used on regular midvalves.  I’m using the same stack I had from the 1st ride.  That stack was my best woods combination from the ’07 forks.

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Below are the stack configurations I’ll be using.  The only change is on the mid-valve.

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