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Triple Clamps - How bent is bent? Sticky forks...

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Greetings all hoping to get a handle on a sticky fork situation.  

 

A bit of history: Being new to dirt riding, I picked up a used 2012 KTM350excf after a year's use by previous owner.  The PO was fast, and large (ie +100lbs over me). I think the bike was raced, but not sure.  When I got the bike the speedo was cracked.  Found out later on that this was due to a hit with a tree.  There are no obvious signs of bent forks or bent anything, but more on that later.

 

Not knowing how dirt bikes are supposed to handle, I stumbled along learning the ropes by hitting the trails. I found myself struggling all the time, like I was fighting the bike and the bike was winning. I can't keep up to my buds, going fast gets me out of sorts in a hurry - loss of control feeling.  To compare I just recently managed to try out a buddy's `13 350excf and wow I was stunned.  Suddenly I wasn't overcome by fear and general sense of jitter at speed.  I could rip down the same trail 25kmph faster and feel more confident.  I wasn't as tired after 15mins of hard riding. We weigh the same, his bike is completely stock.

 

At that point, I realized my bike's suspension was not right for me. I assumed the bike had been re-sprung to heavy springs, and possibly re-valved also.  `The journey begins...

 

Aside from how glorious his bike felt on the trails, comparing the two bikes side by side in the driveway I saw differences. My buddy's front forks seem to move effortlessly and not stick anywhere on gentle prodding. Standing beside his bike with no rider, I could gently push down on the front of the seat, and see his forks compressing and rebounding when I let go. Sweet.  My forks however don't do that.  In fact, if i push on the same spot nothing happens. Forks don't compress. I have to really hammer down to get some movement started.  In another scenario - if I grab the front brake and pull backwards to extend the forks, when I release the brakes the forks 'stick' fully extended. I have to push down on the front to get them to move - once moving they return to a normal free-sag location.  From there down they seem fine.  Point is, I see a real difference in behavior between two supposedly identical bikes.  My OCD mission is to try to get my forks behaving smoothly, as they should.  If I can get there, I just might be able to keep up to my mates :)

 

What I did:

- I started with new springs front a back, and new bushings, oil, and seals - RaceTech springs, OEM fork rebuild kit for seals and bushings

- Lubed seals

- Checked fork action without springs with cartridge disconnected, seem fine; left fork is a touch stickier than right but not too noticeable; outer tube slides down inner tube smoothly

- tried to check for bent forks by rotating with a homemade run-out gauge - seems ok (but testing not super accurate)

- verified fork action off the bike - compress and rebound seem smooth with no stiction, both forks seem the same

- forks appear to be in great condition - no scratches, dings, obvious bends, etc etc.

- Check stem --> seems fine with no binding when rotating bars

 

Mounted forks and wheel:

- ensured fork alignment was correct, using the various techniques found online

 

Still same problem. Forks sticky top 3" as described above.

 

Next:

- checked for bent axle on glass - fine

- Pulled triple clamps and checked for gaps on glass - this is where I found slight gaps, no idea if the gaps are bad enough to warrant replacement

 

Can someone look at the pics below and tell me if the gaps are bad enough to do something about? What is ok? Is there any tolerance on allowable gaps?  Should there be no gaps, period?  I would expect a perfect lower and upper clamp to have zero gaps. However I don't have my hands on one and can't compare.  The surface I used to test is flat.  Gap shown by sliding paper until stop.

 

 

Lower clamp left side showing no gap:

2014-08-15 10.59.04.jpg

 

 

Lower clamp right side showing slight gap:

2014-08-15 10.58.56.jpg

 

Upper clamp showing gap while pushing down on one side (ie very very slight wobble):

2014-08-15 10.57.37.jpg

 

Upper clamp showing gap at rest:

2014-08-15 10.57.46.jpg

 

 

 

Any tips appreciated - at my wits end. Based on gaps above, should I look at new triple clamps?  Hate to shell out with no improvement but that is part of the game with D.I.Y.
Edited by shawzy

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You should edit out the first two paragraphs to make your post more concise and to the point.

 

So, your forks feel good off the bike.  If your forks slide smoothly into the triples without having to really force them then the triples are probably fine.  If it's really difficult to slide one or both forks into the triples then there may be an issue there. 

 

Once you get the forks on the bike and you set them at the same height just slightly tighten one of your top clamp bolts on each side.  From here you want to flip the axle around and slide the big end into the fork lug and make sure it slides in.  You're checking to make sure the end hasn't be mushroomed and will allow the axle clamp to float where it naturally wants to rest.  If it slides in ok then flip the axle around and slide it in normally.  You should be able to slide the axle into place and tighten it.  You shouldn't feel any real binding.

 

Assuming that's all fine then tighten all your triple clamp bolts to a lower torque than what you've been using.  Try using around 12ftlb top and bottom.  Put the wheel on, slip in the axle and tighten it down to around 40ftlbs.  Then tighten the left side pinch bolts to around 10ftlb.  Then go to the right side fork lug and tap a small flat head into the gap.  Make sure you can freely move the lug left and right a few mm without issue.  If you can then remove the screw driver, grab the front brake and press down on the front end 4-5 times.  Then tighten the pinch bolts on the right side to about 10ftlbs.

 

See how the above works for you.

Edited by kan3

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kan3 thanks for the tips.  I thought to provide as much background as possible to help my diagnosis, perhaps my thread title should be changed.  

 

I tried your suggestions. Axle flip --> no problem, axle slides through easily.  Alignment procedure - done as you described.  To verify I tried a slight wedge-in and wedge-out off the 'zero' position and it made it worse both times. Pretty confident alignment is fine after repeating your procedure above.  Did not help my issue unfortunately.  Loosing the pinch bolts on lower clamp didn't help either - dropped to 10ftlbs.

 

Your statement "If it's really difficult to slide one or both forks into the triples then there may be an issue there".  To slide my forks in, I have to rotate them as they do jam.  I can't slide them in without rotating them back and forth. In fact to get them off I had to spray WD40 all around lowers so they would rotate.  If this is not normal, please elaborate as to what you consider normal.  If I recall, my Kawasaki street bike forks didn't exactly 'slide-in' either without some rotation and that was from new, but other than that I have no other reference points.

 

Appreciate the help

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They should slide in by hand with no lube needed , sounds like it could be bent

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If they are slightly bent, when I torque pinch bolts I wonder if this is stressing the forks enough to make them stick as I describe. I hope to swap forks this weekend with my bud to see before I drop coin on new clamps. New clamp is around $400 from what I see out there. Nervous to buy used.

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Often you can get used take offs

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OK have an update. Turns out the triple clamp may be a red herring. I inadvertently installed stiffer springs by mistake.

All along I thought I was comparing 2 bikes with the same springs. Not the case.

Here is how I got here:

Went on Racetech site and looked up my ride. Racetech states a stock spring rate of 0.46kg/mm (4.5 N/mm). OK great, I ordered those. I loved the feel of my bud's stock ride so I figured it would be perfect. Their built-in spring rate calculator suggested 0.44, but I opted for the stock weight of 0.46.

However, looking at owners manual, the stock spring rate appears to be 0.43 kg/mm (4.2 N/m). The manual suggests a spring rate of 0.45 kg/mm (4.4 N/m) for up to a 210lb rider! In addition, the manual suggests a spring rate of 0.41 kg/mm (4.0 N/m) for my weight range.

Why Racetech suggests 0.46 kgf/mm as stock for my 350 excf is not clear to me. This translates to a 250lb rider according to the manual. Recommended spring rates differ substantially I am not quite sure where to go. Might try going with rate of .42 and see what happens. Gamble at this point. I know rates are subjective and everyone may have different preferences but wow this delta is huge.

Wish I saw the spring rate info in the manual before I ordered springs. Regardless I'm sure Racetech will make it right. I've had really good experiences with them in the past and they know their stuff.

I will attempt to swap the springs to a lower rate and try this all over again. I will post my results.

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OK have an update. Turns out the triple clamp may be a red herring. I inadvertently installed stiffer springs by mistake.

All along I thought I was comparing 2 bikes with the same springs. Not the case.

Here is how I got here:

Went on Racetech site and looked up my ride. Racetech states a stock spring rate of 0.46kg/mm (4.5 N/mm). OK great, I ordered those. I loved the feel of my bud's stock ride so I figured it would be perfect. Their built-in spring rate calculator suggested 0.44, but I opted for the stock weight of 0.46.

However, looking at owners manual, the stock spring rate appears to be 0.43 kg/mm (4.2 N/m). The manual suggests a spring rate of 0.45 kg/mm (4.4 N/m) for up to a 210lb rider! In addition, the manual suggests a spring rate of 0.41 kg/mm (4.0 N/m) for my weight range.

Why Racetech suggests 0.46 kgf/mm as stock for my 350 excf is not clear to me. This translates to a 250lb rider according to the manual. Recommended spring rates differ substantially I am not quite sure where to go. Might try going with rate of .42 and see what happens. Gamble at this point. I know rates are subjective and everyone may have different preferences but wow this delta is huge.

Wish I saw the spring rate info in the manual before I ordered springs. Regardless I'm sure Racetech will make it right. I've had really good experiences with them in the past and they know their stuff.

I will attempt to swap the springs to a lower rate and try this all over again. I will post my results.

 

 

hey friend,

id call a few places and buggem about what the right spring rate for your weight is.

like mx tech.....

 

also.

to further ensure correct alignment you can used the aforementioned procedure with a ratchet strap through the front wheel and attached to the handle bars, crank the bike down as far as you can get her

this will more truly align the fork lugs on the axle.

 

personally i take the top caps loose and that allows no spring pressure you can bottom the suspension and perform the fork alignment procedure... it doesnt get any better than that :]

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EnglertRacing - cap off idea to bottom out is brilliant.  Wish I thought of that! Does it get messy with the springs dripping fork oil everywhere?

 

Talked to Race Tech. They are shipping me 0.42 today, no questions asked. Brilliant.  They aren't waiting for my 0.46 to get to them first, much appreciated.  Hoping the 0.42 are not too soft, but if they are I can return those for swap 0.44.  As I get better at riding I may graduate to the 0.46 one day....

 

As to why Race Tech is claiming my KTM 350 exc-f has a stock spring rate of 0.46?  They pull springs off a factory bike and test them in their lab. So - perhaps they got one out of the factory with stiffer than normal springs, perhaps the calibration was off, perhaps they made an error and mixed springs with another bike - who knows.  Point is I wasn't able to convince them to change their web site to 0.43 (as per manual).  Too bad, as this is misleading.  

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What is your weight?  Those manual recommended spring rates are too low.  They're recommended rates from their calculator are a bit more inline.  Unless you're someone who soles rides tight single track.

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I am 150 lbs no gear. Owner's Manual recommends 0.41 at this weight. RT Calculator pegged me at 0.44, I opted one step down to .42 as a compromise.

I ride single track mainly and some fast double, and this is my second season so lots to learn still. If Race Tech offered a 0.43 I would do that but they don't. Others tell me the calculator tends to run a bit stiff.

I figure I will try the .42 out. If they turn out to be a wash i will swap out to 0.44. The .46 were too stiff for me after a short jaunt.

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Ktm often supply springs mismatched , eg one 0.46 and the other 0.44 , so if they tested only one spring they would get the wrong rate

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I'm not sure if they do it in purpose as every 450 my local shop had tested had 0.48 one side and 0.52 the other , seems like it was intended

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I guess that is one way to get a varied spring rate in between the rates installed, assuming one can average both rates together but I am quite surprised if this is intentional. If my 0.42 turn out too soft perhaps I will swap back to a 0.45 in one fork only :)

I thought a varied spring rate between forks would allow the front wheel to 'twist' as the load or force on the axle would differ from side to side. I see this as not good, and assume it would cause binding in fork action. I am just thinking out loud here, curious what reality is.

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