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Front End Shake

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Hey guys,

I just picked up a KTM 450 SX-F and took it out for my first ride on Sunday.  Love the bike!  I do off-road riding, not track.  The power is incredible and the handling is awesome.  The only complaint I have is that on a gravel road or pavement in 4th gear I get this violent front end shake.  I'm not sure I would classify it as "head shake" or not.  It's not side to side, it's more like a harsh vertical vibration in the forks.  I've been told to check my bearings which I have yet to do.  I'm wondering if anyone can give some suggestions what to look for?  I haven't set the suspension up yet, but definitely plan on doing so.  Please help, I love the bike and can't wait to get out riding again!

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Sounds like the front wheel balance , mx bikes are not balanced and at high speeds you can feel the effect of this (the rim lock ) not sure if you can balance the wheel in any way ?

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Sounds like the front wheel balance , mx bikes are not balanced and at high speeds you can feel the effect of this (the rim lock ) not sure if you can balance the wheel in any way ?

 

I balance my dirt bike wheels, it takes a little more weight due to the rim lock...

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yep...sounds like it's out of balance.

 

do you have a rim lock? probably...and when the tire was mounted, it was probably not balanced to compensate since many people don't bother to do that for dirt riding. but, when you ride it on pavement like that...yikes.

 

rather than add a bunch of weight to balance mine, i put a second rim lock 180* across from the factory one. it automagically balances the wheel/tire...i never need to add weight to balance them (the rim locks balance each other, and i think they are so heavy, they sort of overwhelm any other minor imbalances--or something, works great in any case). just another option.

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Sometimes it helps to have an uneducated opinion on such a thing.  I am sure these guys are right.  Think about a truck.  When the wheels are out of balance the truck will shake something awful.  What a great solution to such a disappointment on a new bike.  Maybe the dealer squirted some tire repair gunk in the tube?  Just something to think about if the wheel doesn't balance out.  Oh ya...make sure they balance the rear out as well...it might feel like the front only but maybe not.  Congrats on a perfect bike and that would be my top choice for a 450cc too!

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What's the best way to determine if it's out of balance? Can a guy tell if you throw the bike on a stand and spin the tire or something? I've also been told a tire can be out of balance if the spokes aren't tightened correctly and evenly?

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What's the best way to determine if it's out of balance? Can a guy tell if you throw the bike on a stand and spin the tire or something? I've also been told a tire can be out of balance if the spokes aren't tightened correctly and evenly?

 

best way is with a balancing stand, but if you don't have one of those, you can try doing it on the bike.

 

back the brake pads off so they do not contact the disc at all (maybe even pull the pads just to be sure).

 

now, your wheel should spin very freely and easily and consistently with no resistance, crunchiness, variation in drag, etc. should spin on its own for a good long time. (you won't get it as friction free as on a balancing stand, but maybe close enough). assuming that is the case...

 

spin it and pay attention to where it stops (probably with the rim lock at the bottom). do that repeatedly and see if it always stops in the same spot (e.g., with the rim lock always at the bottom). if it does, that point at the bottom is the heavy spot. add weight directly across from that until it stops at random spots. (note, though, that if your wheel bearings are causing too much drag, the wheel can stop at random spots even if it is actually way out of balance.)

 

as for the spokes, yeah, that could cause a problem but is much less likely. my method for checking them is just to flick them all with my fingernail and listen to them. they should all sound about the same. if you have one that "clunks" while the others all "ping", that clunking one is loose.

Edited by LittleRedToyota

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try lowering your forks if they are dropped down to help turning it will give u head shake as well

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We'll, I picked up some stick on weights and spin the tire on a stand without the brake calliper and sure enough, the rim lock stopped at the bottom every time. I placed some weight straight across the rim from that and it got better, but was still shaking pretty bad. So I took a chance and stuck a bunch of weight across from the rim lock on the rear tire as well. It seems way better, but I haven't had a chance to rip in it. I will post results when I get the chance. Thanks guys!

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Steering stem could be torqued to loose or vaguely tightened. Rolling it foward and hit the front brake if it jerks, that may be your issue. Ive found when my front master cylinder is loose it also causes this but in a far less dramatic action

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Tighten crown nut. The one under triple clamp. So bars bounce back one inch when pushed hard to the stops. Yes over tight is ok

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