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Old 03-03-2013, 07:20 AM   #1
Boon Booni OP
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640 Adventure Fork Stiction

I've been cluttering up the index for too long on this, so I'm starting a thread on it.

Picked up a new to me 2002 640 Adventure back in October. She's got 28,000 miles on the clock. It's got 48mm 2 bushing USD forks. Noticed on the test drive that the front end was stictioning up a bit. PO said the forks had been re-built/re-valve about a year and a half prior. I don't know if he'd changed the oil since then.

Brought the bike home, and set about re-sealing and re-greasing as much of the chasis as possible (and fixed and oil leak or two on the motor to boot).

I took the front end off and before removing the forks I checked them with a plate glass to see if they were properly aligned.



They were a little out of alignment, but nothing horrible.

I proceeded to tear the forks down to the valve stacks, drained the old oil which had a a bit of metallic flakes in it, but didn't look horrible either.

Found one of the rebound valves corroded and stuck cleaned it up. Bushings looked OK to me, (but that's not something I have a whole lot of experience examining), seals seemed OK so I cleaned everything up and re-assembled the forks. (re-used all the seals and bushings) Poured in some fresh Maxima 5w racing fork fluid and set the air gap.

I got no pics of the initial fork re-build.

Took a while for parts to come and time to come and temperatures to be nice enough to spend hours in my under-heated garage but finally got everything back together. Made doubly sure that the axle wasn't binding in the right side fork clamp. I'm able to move the clamp along the axle a few mm in each direction.

The rebuild definitely made a difference. When I first got the bike, 2-3 pumps and the forks would feel like they ground to a halt. Now the stiction didn't feel mechanical or as potentially damaging.

Got my first 200 miles on the bike last weekend and could still feel the front end stictioning up. When I last re-built my Vstrom, the front felt a little sticky on the new seals for the fist few hundred miles, but freed up nicely after that, and I was hoping the same for the KTM, but no.

This is what I'm finding at the moment...



This is with me on the bike. Zip tied a brazing rod to the brake line and used the decomp cable as a marker. The top zip tie is pulling all the way up on the bars and letting the suspension settle. The lower zip tie is pushing down the bars and letting the suspension settle. That's just over 1" between them. As a comparison, my V-strom has the width of just 1 zip tie between the two marks.

Anyhow, spent some time out in the garage last night. I removed the wheel and double checked the fork tubes were parallel. First with the plate glass again, and next with this fellow..







This was the first go around where I was only able to get about 5" between the two measurements because of the base, but I re-jiggered it so that I was able to get about 9" between the two measurements. What I found was that the top of the measurements was about 0.01" tighter than the bottom. So the bottom of the forks splayed out a little from the top. I checked and re-checked these measurements for repeatability and accuracy. I had about 0.001"-0.002" deviation on repeated measurements.

IMHO 0.01" over 9 inches is not a lot and probably within the tolerance of the slop in the bushings but it's more than I'd measured on the BMW you can see in the pic.

So my next step was to see if this mis-alignment could be the problem. I re-installed the front wheel, and pumped the front end to verify that things were still binding up. Then jacked the front up a little and removed the fork springs.



I re-installed the caps and ran the forks through their complete travel. They moved smoothly all the way up and all the way down. The weight of the front wheel alone is enough to pull the front down completely.


I tried intruducing a bit of stiction by forcing the right clamp over on the axle and locking it in.



So by forcing some sitction into the system, I can cause the wheel to lock into place. But as soon as I release the clamps on the right side, the whole assembly slides down on it's own. And once I re-tighten the right clamp everything moves up and down freely.

I then removed the front wheel and moved the sliders by hand. Both of them move smoothly, and the left side will drop on it's own due to the weight of the caliper. The right not so much. When moving the sliders slowly by hand they will stutter. There's a light catch and grab going up and down and it's never in the same place. I popped the dust seals and the catch and grab decreased, but is still there.

My next step will be to remove the caps and run the sliders through their stroke again. This should eliminate any possible internal hydraulic hiccups.

Might be a few days.

Any and all comments or questions welcome.

Stay tuned for the next installment of As the fork turns...
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Old 03-03-2013, 10:03 AM   #2
gunnerbuck
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Do you bleed the air out of the forks at regular intervals? I find that I have to do this once a day when I am racking up the miles... What kind of fork seals are installed in them?
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Old 03-03-2013, 11:07 AM   #3
Boon Booni OP
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Quote:
Originally Posted by gunnerbuck View Post
Do you bleed the air out of the forks at regular intervals? I find that I have to do this once a day when I am racking up the miles... What kind of fork seals are installed in them?
I only have about 300 miles on the bike since I picked it up in October, 200 of which came last weekend so I don't know about bleeding the forks on a regular basis. They do have bleeder valves and I did release the pressure before starting this examination . I also removed the bleeders completely so I could move the forks through their stroke with the caps on.

I called Neil the owner of Hitchcock industries who was the last one to rebuild the forks. He installed KTM oem seals in 2011. I don't think he swapped the dust seals (not on the invoice) and he said since he didn't replace the bushings he would have inspected them to verify they were in good shape.

Neil's opinion is that it's possible the lower bushings are worn. That it's not uncommon for mud to get under the seal and damage the lower bushings.
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Old 03-03-2013, 11:53 AM   #4
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Just a question, have you ridden the bike with a full tank yet?
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Old 03-03-2013, 12:19 PM   #5
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Just a question, have you ridden the bike with a full tank yet?
Yep, started the day off with a full tank.
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Old 03-03-2013, 12:29 PM   #6
gunnerbuck
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During the coarse of a day of riding the forks may build up pressure inside, you'll know when it happens because the forks feel harsh, almost like stiction on the compression... Anytime I get this feeling I'll pull over, put the bike up on the centerstand, elevate the front wheel and press the bleeder buttons... Almost always you get a hiss of air as the pressure is released and it returns to zero...
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Old 04-02-2013, 08:08 AM   #7
Boon Booni OP
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Progress!

Need to upload the photos, but I replaced all 4 bushings, forks seals and dust seals.

With a quick and dirty fork installation stiction has decreased to under 1/2 an inch and it doesn't feel like a mechanical binding at all.

Photos to follow...


Word to the wise, if anyone tells you all KTM 48mm forks are the same, don't believe them.


With that in mind..



KTM Fork Maintenance Kit R140.20

... this appears to be a very good deal. $80 for enough parts to rebuild both forks. Dust Seals, Seals, Bushings, and various inner bits.

I was building a kit for myself with individual parts and was well over that price with seals and bushings for just one leg.

At least it's a good deal if you don't mind modifying your old bushings.
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Old 04-02-2013, 08:57 AM   #8
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It does look like this kit comes with SKF seals, I have not had much luck with them holding up... I believe my original 03 fork seals were marked NOK, were built somewhat tougher and gave a couple of years of service {25 K miles}...
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Old 04-02-2013, 10:05 AM   #9
Boon Booni OP
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Quote:
Originally Posted by gunnerbuck View Post

It does look like this kit comes with SKF seals, I have not had much luck with them holding up... I believe my original 03 fork seals were marked NOK, were built somewhat tougher and gave a couple of years of service {25 K miles}...
According the the parts guy, SKF are now Oem equipment. The seals I removed were marked NOK.
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Old 04-02-2013, 03:56 PM   #10
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Quote:
Originally Posted by Boon Booni View Post
Word to the wise, if anyone tells you all KTM 48mm forks are the same, don't believe them.

....


At least it's a good deal if you don't mind modifying your old bushings.
To follow up on this thought.

Took the usual 2 weeks or so to get the kit.



Everything looked great. The consensus seems to be that SKF seals aren't as good as the original equipment, but I was told that SKF is now original equipment so we'll see how it goes. Aside from the color, they seem to be nearly the same design as the NOK seals that came out.



But upon dis-assembly of the first fork I find this.







The new "leading" bushing is 8mm shorter than what came out of my forks. Guess that's what the +8mm in the part number means.

LEADING BUSH 48X52X12+8MM

The top bushing is the correct size. Think think think.. Do I want to re-use the bottom "leading" bushing? No, I'm in here to replace those bushings and that's what I'm going to do.



Chop chop, grind grind and I've modified the old bushing to become an 8mm spacer for the new bushing. I split the old bushing down the middle, and grind out about 1mm from the inner diameter of the old bushing. I make two 8mm spacers out of one bushing.


Even though the kit came with a few internal bits, I decide I'm just here to to the bushings, so everything goes back together.




Use electrical tape to protect the seals..



I notice that removing 1mm from the inner diameter of the old bushing would allow the top bushing to slip inside of it. Because of this I decide to locate the spacer below the "leading" bushing so as not to damage the top bushing the next time I've got to slide hammer the seals back out.

Everything all clamped up in my vise with nylon inserts.




Use home made driver to drive bushings and seals back into place..



Notched to allow clearance of the seal lip.





Used the new washer and snap ring from the kit.




Snap ring dropped into place with a satisfying snap.




Easiest way I've found to get damper assembly in place.




...and






Front feels better, still a little bit of stiction, but now it's below 1/2" between resting points.

I'm hoping it'll get better as the forks get run through their stroke a few hundred times.

I'm convinced it was the old bushings that were binding things up. The old top bushing was showing signs of wearing through to the copper underneath and the old bottom bushings had a few little bits of aluminum embedded in them.



As long as the SKF seals hold up, the kit is a steal as far as pricing on everything goes. But you've got to get some sort of spacer in there or there will be 8mm of play for the new bushings.

I don't have any sort of fancy milling machines. I marked the center line of the old bushing and used a dremmel cutting wheel to split the circumference of the old bushing. I used a bench grinder to get the thickness close to 8mm. Then I flat sanded the bushing until it was 8mm thick. I then used the dremmel again with a mini sanding wheel to remove the 1mm from the ID of the bushing to allow it to clear the fork tube. Didn't take too long to make them.
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Old 04-02-2013, 09:29 PM   #11
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Boon,
Nice work, been down the rebuild road a couple of times.

For a seal driver in a pinch you can use a piece of radiator hose to seat the seal. Yours looks much nicer.
bill
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Old 04-03-2013, 08:33 AM   #12
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Boon,
Nice work, been down the rebuild road a couple of times.

For a seal driver in a pinch you can use a piece of radiator hose to seat the seal. Yours looks much nicer.
bill
Thanks, I don't usually document my maintenance but I'd gotten a few PM's when I first described the various bits of work I did to the bike over the winter.

I got to tell you I thought I was was in "high cotton" when I found that fork maintenance kit online. I couldn't believe the price compared to the individual pieces (just the two bottom bushings alone are $100 for the pair from KTM). I was quite deflated when I first discovered that the bottom bushings were 8mm too short. I had called around and gotten the opinion that all KTM 48mm USD forks were the same, so I didn't expect to run into this problem.

Seems like the smaller bushings are used on the 950's and 990's.
DU-BUSH D48XD52X12DDL02
So I'm sure they'll work fine on the 640.

Unless the DDL02 is code for +8mm
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Old 04-03-2013, 08:55 AM   #13
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Try Honda SS-19 fluid, it helped with my stiction problem on a different bike.
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Old 04-03-2013, 09:00 AM   #14
gunnerbuck
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Quote:
Originally Posted by Boon Booni View Post
Thanks, I don't usually document my maintenance but I'd gotten a few PM's when I first described the various bits of work I did to the bike over the winter.

I got to tell you I thought I was was in "high cotton" when I found that fork maintenance kit online. I couldn't believe the price compared to the individual pieces (just the two bottom bushings alone are $100 for the pair from KTM). I was quite deflated when I first discovered that the bottom bushings were 8mm too short. I had called around and gotten the opinion that all KTM 48mm USD forks were the same, so I didn't expect to run into this problem.

Seems like the smaller bushings are used on the 950's and 990's.
DU-BUSH D48XD52X12DDL02
So I'm sure they'll work fine on the 640.

Unless the DDL02 is code for +8mm
The first 48mm forks used on the 640 A {01-02} were a little different inside, In 03 they changed them to more of a current design.. Then the 04 models {Europe} and 05 received the 950 forks with the big axle brackets and double disk hardware but the internals pretty much remained the same as the 03...

Did your forks have a metal spacer tube about 6" long on that slid on between the slider bushings? I did not see one in your pics, so maybe the 02 forks were not equipped...
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Old 04-03-2013, 02:05 PM   #15
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Quote:
Originally Posted by gunnerbuck View Post
The first 48mm forks used on the 640 A {01-02} were a little different inside, In 03 they changed them to more of a current design.. Then the 04 models {Europe} and 05 received the 950 forks with the big axle brackets and double disk hardware but the internals pretty much remained the same as the 03...

Did your forks have a metal spacer tube about 6" long on that slid on between the slider bushings? I did not see one in your pics, so maybe the 02 forks were not equipped...
Mine don't have the tube. I remember reading about the triple bushing forks? Didn't they use the tube to hold the middle bushing in place?
Is the current design triple bushing, or was that just a short run of forks?
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