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Headshake

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My sons kx85 started getting headshake again on landings and it progressivly got worse and worse. 2 weaks ago he got it bad after a landing and bit hard. Broke his collar bone. So i have alittle time now to try to figure out what is causing it. I moved his front forks up before ( staying within limits) to correct it after a fluid change and that fixed it. But it returned with no adjustments. He's only 12 and cant seam to tell me what the front forks feal like. Which I understand. I do own and ride a 05 kxf250. Any ideas would be more than i have right now. Yes I do wish i wouldv'e figured this out prior to the crash. And no one needs to tell momma about this question. LOL

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Make sure the preload on the steering stem bearings is not to loose.

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Usually a high oil height or stiff springs cause this problem. How much does your son weigh? What oil height are you currently running?

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My son weighs 85 lbs and I set the oil level per spec and was very miticulouse about it. I forgot i did change both steering stem bearrings and races, but again, was very careful not to over tighten. There is no play at all in the steering stem and the front will turn with no effert, actually it wil fall to the left or right depending on the floor level with the bike on a stand. Maybe I need to reservice the front forks and double check my method and maybe go with less oil ? I did shave his seat down , he's also short for his age.

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Usually a high oil height or stiff springs cause this problem. How much does your son weigh? What oil height are you currently running?

WRONG ANSWER! fork springs that are too soft cause headshake. Buy stiffer fork springs, or get him a steering stabilizer, I would reccomend the fork springs.

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Make sure the preload on the steering stem bearings is not to loose.

I agree, sounds like you might need to just tighten up the collar.

You still want some resistance when you turn the bars to each side.

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I agree, sounds like you might need to just tighten up the collar.

You still want some resistance when you turn the bars to each side.

🙂

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Fork springs that are too soft cause headshake when you are braking because the front forks are diving. If he's landing off the jump he's most likely accelerating and it's most likely accuring after the suspension unloads. If your son is 85lbs he's definately on the light side for the stock springs. Put in some .27's in the front and a 4.3 in the rear. The reccomended weight for a stock KX85 is 110lbs. Sorry but his springs aren't soft.

With that said, I would agree with the other guy's however and check into tightening steering stem collar it would definately help in this situation.

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Also check the rear sag, if its set too high this will effect the steering geometry of the bike and could cause headshake.

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is head shake when the bars start slamming from side to side. theres a field that i ride in sometimes that has groundhog holes and ill be flying across that thing laid out in 5th gear and all of a sudden my bars will start going from side to side, pretty much fully turned. never wrecked because of it, but i don't like going very fast in that field anymore.

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don't move the forks up through the triple clamps move them down as far as they can go for more stabilty, and soften the preload and slow down the rebound and soften compression on the rear shock

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It won't be the most economical route ....

But a stabilizer would be the quickest way to stop it.

I've been riding with one for the last three years for the same reason.

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go to www.racetech.com and see what spring rates they recommend using their calculators..or any ofthe other spring manufacturers.

Another thing to check on the steering nut is place teh bike on a stand so the front tire is off the ground and have someone hold the bike or your son sit on it 🙂, then grab both forks on the bottom and pull/push back and fork and see if you have any free play in the steering head. If you do you will feel it rock back and forth and make a knocking sound. If there is freeplay you can try tightening up the steering nut or you could have a bad bearing.

Saved the dumb question for last...your son isn't grabbing the front brake to get the front end down if it is too high does he...instead of using the back brake w/ clutch pulled in? If he is this can also cause head shake when he first lands due to the front tire not rotating. I have done that before and got headshake when I landed due to that reason.

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I was always under the assumption that if everything checks out(sag, clickers are not out of wack, seals not leaking and spring rate correct) that to cure headshake you either slide the forks down in the clamps(Make the top clamp flush with the fork) and turn "in" the the rebound adjuster.

Erik

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No he's not pulling in the front brake. But as far as im concerned there arent' any dumb questions to ask a 12 year old in this regard. His forks are set at the upper limit, high in the triple clamps, I will move the lower in the clamps. I wrote down all the things that you all suggested i try or check and Plan to spend the weekend on the bike. Lots of good information i sure appreciate all the advice. I don't understand a whole lot yet in regards to the front set up yet but i plan on figurring it out soon and appreciate the head start you all gave me. Plan on taking bike to track and getting one of the hot rod kids to check it out for me and help dial it in. There are a couple that are same size as my boy but seam like they were born on a bike. Thanks again.

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What are your sag numbers? This bike is a bit out of balance in stock form (stiffer in the back) and at 85 lbs. you may find that the stock rear spring is a bit stiff. What happens then is by raising the forks up more it will be a little more unstable.

I would make sure to get the right spring rate on the rear and then lower the forks in the clamps some. I have found that they work best with about 12-15mms sticking up out of the clamps.

doc

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I found this the other day:

HEADSHAKE / HARSHNESS:

FORK - Is generally caused by too much compression damping in the forks. Soften compression 1-2 clicks. Lighter riders for the size bike you are riding may find it necessary to change to softer fork springs. Too much rebound damping can also cause a “packing” situation in which the damping holds the forks down in a stiffer area of the travel than is needed. Soften rebound damping 1-2 clicks. Other causes can be : a) improper fork installation or binding of the fork. 🙂 improper shock set up which causes the fork to ride too far into the stroke.

Ziggy Tip: Too much air pressure in your front tire will cause some deflection and harhness feel to your forks. We recommend only 11-13 psi. of pressure.

Find more info here: http://www.factoryconnection.com/index2.htm Look at setup tips then troubleshooting.

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You know I started getting bad headshakes on this one landing, after I upped my front tire pressure. Guys were getting flats, so I put in a couple more pounds and voila, I started getting headshakes, thanks. I was going to start chasing suspension problems.

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