YZF400 Headshake

[m2g4b]

I OWN A 1998 YZF400 AND I GET TERRIBLE HEADSHAKE AROUND HIGH 3RD GEAR AND BEYOND. I HAVE HAD THE FORKS REBUILT AND AM USING THE STOCK SETTINGS FOR THE FORKS. I AM AROUND 165 POUNDS AND RUN A FRONT AIR PRESSURE OF ABOUT 17 POUNDS. ANY HELP ON THIS SUBJECT WOULD BE GREATLY APPRECIATED.

[Ramrod]

Try running 11-12lbs. pressure! 17 is way too high.

[sirthumpalot]

I get the same thing with my '01 when on strait flat ground. I'm also about 160# without gear and use the stock suspension settings. Tire pressure doesn't seem to affect this for me. I've read that a few people have used a steering stabilizer with much success so maybe this is worth looking into. I don't know if playing with the clickers would help or not. At the track where I ride there is only one strait long enough for me to notice the head shake and it doesn't really cause much problem so I haven't put any effort into trying to get rid of it myself. Hopefully someone else here will have better suggestions for you.

[m2g4b]

OKAY, THANKS SO FAR, ILL TRY SOME OF THESE THINGS THIS WEEKEND. AS FAR AS THE STEERING DAMPNER, IVE HEARD THAT TO BUT I AM TRYING TO FIX IT ON A BUDGET FIRST. AND ABOUT MOVING THE SHOCKS UP IN THE TRIPLE CLAMP, I AM ABOUT 5'10" WILL THIS CAUSE TO MUCH "BULL DOZZING" IN THE CORNERS OR HAVE YOU HAD THIS PROBLEM, MINE ARE FLUSH WITH THE TOP AT THIS POINT. THANKS FOR ALL THE SUGGESTIONS!!

[dirtbikebd]

As far as "bull dozing" I haven't had any problems with that, BUt I am 5'5". My friend has ridden it, and he is aroound 5'10" and he hasn't had any problems. I would try bringing up the forks a little, like I said not too much, or you will get that. I did mine where there is about a 1/2 an inch on the top. On my forks there was an engraved line and that is where I lined them up

[Merfman]

The very *first* thing I'd check is race sag. Dial it in

to around 4". My 98YZ was very sensitive to sag and

headshake.

[MX_Tuner]

Merf, what the heck are you doing here?

What he said. Check the sag first, make sure it is at least 100mm with you standing on the pegs, not sitting on the seat.

Moving the forks up in the triple clamps will steepen the steering head angle, making the headshake worse, not better.

What weight oil was used in your forks? What was the oil level set to?

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MX Tuner

[dirtbikebd]

I had bad headshake when I first got my 00 YZ426. To a recommendation of a friend, I moved the front forks about a 1/2 inch up in the triple clamps. The tops of the forks were almost flush at the top. I did help with my headshake, still a little bit, but much better than it was. But don't go to far because it will cause other problems. There is a happy medium. Hope this helps

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<A HREF="http://profiles.yahoo.com/techmanbd

'00" TARGET=_blank>http://profiles.yahoo.com/techmanbd>

'00 YZ426F

[This message has been edited by dirtbikebd (edited October 09, 2001).]

[This message has been edited by dirtbikebd (edited October 09, 2001).]

[Merfman]

Originally posted by MX Tuner:

Merf, what the heck are you doing here?

What he said. Check the sag first, make sure it is at least 100mm with you standing on the pegs, not sitting on the seat.

Moving the forks up in the triple clamps will steepen the steering head angle, making the headshake worse, not better.

What weight oil was used in your forks? What was the oil level set to?

Uh oh, busted. I figured you'd felt a tremor in the force by now.

My lovely wife bought me a '01 426 last year. I don't race much

any more so this bike is a perfect "dual sport" for me. OTOH,

I have raced it twice, taking a 1st and 2nd while doing so.

And, regarding the headshake, what Tuner said. I can't

imagine what's causing headshake on this bike with the forks

even with the clamps unless it's the sag.

[m2g4b]

Okay, as far as I remember, we used standard 5 weight fork oil does that sound right? and as far as the level, somewhere in between the book specs. Now about race sag? I have no clue what your talking about, please explain...

thanks

[m2g4b]

okay, more info... as far as I can remember we used standard 5 weight fork oil, does this sound right? and the oil level was basically set at the midpoint of the book specs. Now as far as race sag, I have no idea what your talking about, please explain further...thanks

[MX_Tuner]

Gee, my wife bought me a push mower.

m2g4b, try raising the oil level in your forks. Get an infant medicine syringe and add 10ccs per leg. You want to run the oil level a little on the high side to prevent the forks from dropping too much.

The sag setting procedure is outlined in your owners manual. Basically this is the difference between a measurement from two reference points (one on the rear axle area and the other near the back of the seat/rear fender- you just need two points that you can measure from over and over). One is taken with the bike on a stand and the other is taken with the rider (that would be you) ont eh bike. To get teh most accurate measurement, stand on the footpegs and have someone balance you. This means you'll need two helpers. One to measure and one to hold you and the bike upright. You need to aim for 100mm (4") as the net difference between teh two measurements. This can make a huge difference in about a dozen different handling trais (both good and bad).

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MX Tuner

[YZ400Court]

Have you checked the steering head bearings too see if they may be too lose? Also, as they are attached to the oil resivoir, they get really hot and the grease tends to not last long. The result is dimpling of the bearing races. This can cause dramatic headshake. To check for dimpled bearing races, put the bike on the stand (front elevated). Slowly turn the bars side to side close to center. If you feel sort of a stop in the center you know the bearings are shot.

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Pretend it's flat and give it the gas.

[m2g4b]

Thanks for all the information people, I'm sure I can get something to come about after checking all the things mentioned.

Thanks again!!

[Merfman]

One note.. Tuner recommends using a syringe to check

and/or change your fork oil level. That works but I prefer

making the following:

Take a 2" (?)PVC endcap, drill 3/8" hole in the top, off

to one side. Add a small grommet. Insert a straight piece

of rigid tubing, I used copper. Measure whatever oil height

you need from the top of the tubes, from the bottom of the

endcap to the end of the tube. (So when it's inserted into

the forks it's sticking down into the tubes that distance)

Add a syringe to the end of the tubing. Draw out the excess

fluid until the syringe won't pull any more up and voila',

your oil level is correct.

[bbeakley]

Alright, I'm a chemical engineer not mechanical so I'll need a little help with your oil height jig. Please elaborate on the location of the syringe and the procedure. Also, do you have the non measured end of the tubing extending into the end cap at all or is it flush mounted? Please help as this sounds like a cool jig, but I just don't get it.

[MX_Tuner]

I have a similar set up to Murf at home but I meant use the syringe to add oil at the track/trails to dial in the oil height.

At home, I have a vacuum pump with a long metal tube. I use a clothes pin to set the tube depth in the fork.

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MX Tuner

[Merfman]

bbeakly... here's my setup...as best can be done in ascii

anyway...

---+

PVC|

| V rigid tubing

----------|++++++++++

----------|++++++++++ Plastic tubing to syringe

^dist ->|

-----+

Fill your tubes with oil to within an inch or so from the top.

Bleed the cartridge by slowing pulling it up and down.

Measure "dist" from the bottom of the PVC endcap to

the end of the rigid tubing. I have my fluid set to 90mm

from the top of the forks, tubes collapsed, spring out, so

my "dist" is 90mm. Place the endcap over the end of the

fork tube, hold in place and use the syringe to extract

excess fluid.

Does this help?

[Merfman]

crap, that drawing looks like sh*t. sorry.

Lemme try to describe in words...

Imagine the endcap sitting on the fork tube, open end down.

The rigid tubing extends downward into the fork 90mm,

measured from the inside of the endcap to the end of the

downward extension of the rigid tubing. That's your oil

height. I put some clear plastic tubing over the top of the

rigid tubing and attached a syringe to the end of the clear

plastic. The syringe is used only to extract the fluid. If

it still isn't clear, let me know and I'll post a picture of my

jig.

[bbeakley]

My pea sized brain understands now. Thanks for taking the time to explain. I'll give that a shot at my next fork oil change.