Trying to keep the 640 low fender...

Discussion in 'Thumpers' started by sherpa, Jan 6, 2006.

  1. sherpa

    sherpa ...Robert

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    I know I'm late to the 640 party and you "old timers" are sick and tired of hashing around the same old issues...but humor a noob will ya...:lol3

    I've read all the old threads my eye's can take about the low fender issue...and several times I"ve come across mention of somebody heard of somebody else who raised the front fender 3cm or 1" or so... Here's one. I never have run across someone posting that they actually did the "low fender short lift kit mod".

    I'd like to try to keep the low fender...but I need a little education about forks.

    The manual of my 05 says the front forks have a travel of 10.5" or 275mm...well 275mm is actually 10 13/16"...so I'm gonna assume they are more accurate in the metric system and use the 10 13/16" measurement.

    I took some measurements with the bike on the centerstand and a jack under the skidplate to get the front wheel in the air.

    There is exactly 10 13/16" of stanchion tube hanging out of the upper fork tube.

    There is 10 13/16" of clearance between the low fender and the bottom of the lower triple...only 10 9/16" between the fender and the black plastic brake line retainer.

    I need to know what acts as the stop for fork travel. I assume there is something internally? There must be something to prevent the upper fork tube from traveling all the way down the stanchion, until the seal and retaining spring bangs into the lower axle clamp mount.

    I only have 550 miles on my 640, and that has only included catching some small air over waterbars and stuff...never felt the front bottom out yet...the "dirt line" on the lower stanchion is 1 1/4" off the bottom. I have bottomed the Marzocchis on my GS out...and there is still 1 3/4" of stanchion left.

    So I'm wondering if KTM's 275mm figure is a theoretical marketing figure, and the actual, useable fork travel is something less. Does anybody know how much of the stanchion tube is left as "free play" when the forks are bottomed out. I'd like to raise the low fender by that much...hopefully say 3/4"...

    Anybody doing winter maintenance, with the forks out and can give me a figure?...what am I not seeing here? :ear
    #1
  2. meat popsicle

    meat popsicle Ignostic

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    Heya Sherpa,

    Good thought to check clearances; I saw that the 950 folks were worried about an extra inch higher on the low guard too. Sorry if I am missing some nuance to your post; it sounds like you are hoping that there is more room to raise the stock low-boy than the published specs and your measuring afford...

    KTM website lists what you have already figured out:
    Suspension travel front/rear 275 / 300 mm (10.83 x 11.81")

    So you are thinking you have less than a half inch of additional clearance (6/16th) - probably not enough considering the other fun? (longer crossover brake line?) I know you will have fun making the Al tabs to raise the bugger! :D
    #2
  3. Rad

    Rad Done riding

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    Those limp dick 950 folks; I will forward them one of the many emails I get about add'n inches :patch
    #3
  4. rallybug

    rallybug Local Yokel

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    Because you don't need them, Rad? :evil
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  5. sherpa

    sherpa ...Robert

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    My measuring seems to show me that if the spec of 275 mm is accurate... parts are going to go bang when you reach full compression.

    I wouldn't think they would design things to go bang...so I'm questioning the accuracy of the 275 mm specification.

    If 275 mm is inaccurate, and the front forks only travel say 250 mm...then I could raise the lower fender by that 25 mm...

    Does that make more sense ?
    #5
    ialad likes this.
  6. grimmboy

    grimmboy Chris Grimm

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    If its as softly sprung as the rest of the 640's it needs stiffer springs, once installed there would probably be no bottoming issues.
    #6
  7. meat popsicle

    meat popsicle Ignostic

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    Hm... above you stated that 275mm is 10 3/16 and you measured 10 9/16 between the fender and the brake line retainer (bracket) at full extension, so you should have 6/16 of clearance with the stock setup right? Again, I am measurement challenged... I measure thrice and cut, well, usually once :D
    #7
  8. sherpa

    sherpa ...Robert

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    Yeah...I don't know how this "950 Front ended" 640 compares with the other's....seems okay to me so far, but then I'm only 180 lbs...

    What year do you have grimmboy?...lets get together for a ride sometime and compare our 640's..
    #8
  9. sherpa

    sherpa ...Robert

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    Boy...now I know why it's referrred to as the Art of Communication...:rofl ...look again...it's 10 13/16"...not 3...:deal...which means the low fender will most definitely hit the bottom of the lower triple clamp...if there is 10 13/16" of front fork travel.

    I don't think there is 10 13/16" of travel...I think the manual's 275 mm spec is incorrect...I would just like to know by how much that spec is off, so that I can know how much I can safely raise the low fender...
    #9
  10. meat popsicle

    meat popsicle Ignostic

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    :rofl The Art of Reading actually

    My bad... but I have a solution for ya. Put a bit of gum (or something very sticky yet removable) on the brake line retainer and go out for a ride (slow). When you get to the first stop sign slow until you are almost stopped and JAM on the front brake. I can bottom out my forks this way (I do it to trigger traffic lights here :bluduh).

    Where's the gum? :evil :ear
    #10
  11. sherpa

    sherpa ...Robert

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    Yeah...I sorta tried that the other day...but I couldn't get them to bottom out..guess I need to try harder. The Marzocchi's come with an "O" ring on the right stanchion for tuning purposes...instead of the gum trick...I've actually used chalk on the stanchion before to get the same info.

    I was hoping maybe someone had their forks off the bike and disassembled for maintenance...and could give me a conclusive measurement.
    #11
  12. sherpa

    sherpa ...Robert

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    Hey... does anybody have a low fender they want to donate to science...or sell real cheap .:deal




    So meat popsicle...when you do your Jam on the brakes/bottom out routine...is there still a dirt line at the bottom of the stanchion?...measure it for me will ya....
    #12
  13. meat popsicle

    meat popsicle Ignostic

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    There has to be one somewhere that someone doesn't want... probably mostly overseas (EU and down under talk about the high fender mod alot).

    "dirt line"??? :poser I am going for my inagural ride this weekend (I hope) since August 5th when I was T-Boned by an old fella in a pickup. You musta missed that story.

    Plus my 2003 has WP forks so they probably won't tell you what you need to know about your Marzocchis... sorry man. Somebody will show up with an 04/05 and the info eventually.
    #13
  14. bikemoto

    bikemoto Tyre critic

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    G'day sherpa,

    There is no free-play in the fork travel/clearance. My bike in its present form can and does bottom the front guard into the triple clamps. The mudguard has some big scratches and lots of paint flaked away from hitting the bolt heads under the triple clamp.

    According to my measurements, in standard trim, there is something like 18mm more travel than clearance! I've exacerbated that issue by 25mm (pulled the forks through the clamps to balance the Emig lowering links in the rear)...so there is around 40-odd mm too little clearance!! I've also backed off the compression and rebound damping (all the way) in order to get some compliance from the front end. This will also let the fork travel further through its stroke and increase the tendancy to bottom out.

    Remember this front end setup was not designed for the 640; it was ported from the 950. When brand new, I had the guard rubbing on the tyre, possibly because the wider 2.15" rim was fitted after the guard was designed (for a 1.60" or 1.85" rim).

    The '05 640 Adventure has stronger fork springs than previous years.

    btw a simple fork travel measuring device consists of a cable tie around the stanchion (like the o-ring but you can retrofit it).
    #14
  15. sherpa

    sherpa ...Robert

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    Thanks for the confirmation on several bits of info. warewolf...:thumb....my low guard has been rubbing the front tire too...I'll be going to the high guard soon.
    #15
  16. Renazco

    Renazco Formerly AKA Boejangles

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    I have a low fender if you need it, It's been experimented on already but should suffice for your lab work. It's your if you want it just pay shipping..
    #16
  17. AntWare

    AntWare Lost In Translation

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    I noticed the new 990's have a slightly raised front fender so it looks like KTM has addressed this problem somehow. At first glance it looks like it mounts up the same.
    Maybe one of the lads over in U'rup could confirm it.

    IIRC, they've gone to two independent brake lines as well.
    One problem with raising the stock mudguard is the crossover line.
    #17
  18. meat popsicle

    meat popsicle Ignostic

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    Is there some way to restrict fork travel internally? Sorry, I am not a fork guru by any means, but it seems reasonable to think that one could add some spacers to shorten the travel before the (whatchamacallit) "fork stop"?

    Just thinking out loud...
    #18
  19. sherpa

    sherpa ...Robert

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    Sounds great...I can PayPal you some money anytime your ready...just let me know.




    Here's my thinking about the low/high guard issues at present...subject to change at anytime though. :D

    The low guard works better at keeping shit off me and the bike.
    The low guard MAY allow more airflow and thus better cooling.
    The low guard can become clogged with sticky mud causing front wheel lockup.
    When you do get the front clogged with mud, the cross over brake line makes removing the guard a PITA.
    The low guard can bottom out on the lower triple clamp under full compression...although the guard is a very flimsy thing which wont harm anything by hitting the lower triple.

    So...I might try the mods below for awhile prior to converting to the high guard.

    Raise the low guard by 5/8" giving me a total of 1 1/2" of clearance to the tire. That's with the supplied Sahara 3's... will probably be less with knobbies.
    Replace the cross over brake line with a second line direct from the master cylinder.
    Modify the black,plastic, brake line guide that now sits below the lower triple clamp. I'll need a second one of these on the right side for the second brake line. This thing is held on by four bolts...overkill...I'll cut away the center section leaving me with one per side with each held on by 2 bolts...this will give me another 1/4" of clearance before things go BANG.

    The only thing that gives me concern about keeping the low guard...is the issue of The Perfect Rock... getting caught in there and causing the front wheel to quickly lockup unexpectedly...resulting in me taking a little flight over the bars. Has this actually happened to anyone on a 640? :ear I'm not as concerned about taking flight in the mud, because mud buildup takes a little time and gives you plenty of visual warning.

    See anything I'm missing? :ear
    #19
  20. turkish

    turkish Long timer

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    It never happened to me in 30,000 miles with the same front-end on my 950. Rocks would get up in there, but they'd be spit out. Besides, that fender isn't all that strong and anything big enough to jam up and spit you over the bars would probably rip the fender apart first.
    #20