Dumbfounded with headshake problem

[cecilio64]

First off, I apologize for the length of this post, but my mechanic and I are dumfounded by this headshake problem so I want to post as much info as possible. This is my street only bike that has never been down or seen the track. Here goes;

bike: 2006 VFR Vtec no ABS bought new in 2007 in the US, moved to Spain late 2010

problem: head shake on deceleration, with hands off the bars, around 160 Kmh and from 90-75 kmh (I know you're not supposed to ride hands off, but we all do it some time and the bike NEVER did this before) from what everyone says and from my own experience this is one of the most stable bikes built.

done so far: new tires, rebuilt forks, checked spring length for damage during shipping to Spain and everything is OK, checked and repacked steering head bearings, replaced front wheel bearings.

result: deceleration hands off headshake at 160 kmh is gone and headshake is down to 3 or 4 back and forths between 84-79 kmh. Also, found out the other day that this only happens when the bike is straight up and down not if it's on an incline. Also tried a different brand of front tire, new also, to see if it was the tire/brand, but problem is till there.

I believe my mechanic has taken this on as a personal challenge and I'm wondering if I should just live with the result. But, it bothers me too. Anyone experience something like this? Any ideas would be appreciated. Thanks in advance

 

[phild1203]

Normally the first thing that comes to my mind is neck bearings...

Not to be insulting, but after you checked the neck bearings did you adjust them to spec?

 

[steve p]

Hey Miguel, headset bearings is the first thing that comes to mind also and either over torqued or under torqued. I'm sure your mechanic has already checked this though. Tire, air pressure, bent rotor, loose axle, again, I'm sure your mechanic has checked all these things. Keep up posted.

 

[Matt]

have you made any geometry changes? stock sized tires? what's on there now, what what stock?

headbearings, under / over torqued as mentioned, fork height, / rear ride height.

has the bike ever been down? sure the triples are straight? forks go in and slide out very easily? certain wheel balance is spot on? can you try different front wheel? as said, rotors and wheels perfectly straight? check them with a micrometer and magnetic base.

 

[kawaholic]

another vote for head bearings out of adjustment. does the tire have a centerline groove that runs the full circumference of the tire? i had the same problem with my concours running a dunlop d205. are you sure you have the right profile tire? the reason i ask is i had a problem when i switched from a 110/80/18 to a 120/70/18 on my concours. the book calls for a 120/70 and it had the 110/80 on it when i got the bike. i didn't have any problems with the 110/80 but i did with the 120/70. i found out after the fact that dunlop made a special sized 120/70 for kawasaki. unless you bought this one specific model you really needed to put a 110/80 on due to the width of the rim. maybe the tire you have on there is being "pinched" a little causing it to have more of a "pointy" profile?

a few other things to check would be your swing arm bearings and your motor mounts.

hth, tom

 

[cecilio64]

Thanks guys
Bearings were checked and all good, repacked and adjusted to spec. The tries are new, even tried a new different brand to see if it was the brand. Dunlop Qualifiers are what is called for and what was on there before this all started. Nothing was changed geometry wise or other when this started happening. The forks have been serviced, everything cleaned, legs are straight, springs checked compressed and free to be within parameters. I don't know if I can find another wheel but will try. Balance and rebalanced and the headshake is still there. Front wheel bearings were replaced. I will check with mechanic about using a micrometer, but if the rotors were bent wouldn't the problem be constant, especially when braking? and not just at a specific speed when decelerating? I'll have to look at motor mounts and swingarm bearings. The mystery continues

 

[Blinky]

Do you feel a pulse in your MC while braking? sometimes the lever will pulse if the rotors are out of whack.

 

[gkotlin]

Check swing arm bearings and rear wheel bearings. Clean the caliper pistons. Perhaps only one is dragging or the pad is worn on an angle. Check that the rotors are not warped. A warped rotor could be hitting the brake pad as it rotates and causing shake. I'd wonder if the issue happens when applying the brakes or just under deceleration without the brakes. That might help narrow down the area of concern.

 

[sobottka]

add fork pre-load and/or compression to give the front more support when weight is transfered to the front during decell. ...or raise the front of the bike by lowering the forks in the triples ...and keep your hands on the bars!
....whats a v-tec?

 

[dbarufaldi]

Assume this is a VFR? If so, I suggest the following (own a 98 myself).

The ball-bearings in the headstock are notorious for developing an on-center notch after enough miles. Even if they are packed and re-torqued, it will produce odd handling characteristics, including headshake. With the bike on the centerstand, you can sometimes feel it if you move the bars back and forth slowly, with the wheel off the ground. Most of the guys on the VFR lists seem to go with roller-bearings in the headstock, as have I, and it's much better.

Also, on my bike, I get headshake on decel under only one condition - when the bike is overloaded (3 46liter Givis, loaded). This leads me to believe you may want to check the rear shock and rear spring. You don't say how many miles are on the bike, but if it's north of 10K miles, the rear shock is probably shot. If you're more than about 150lbs, the stock spring is probably too soft. These will produce sag and, IMO, produce headshake. ONe clue is that it only happens on the level, not a downward incline. This may be because on the level, there is less weight transfer to the front tire. The unweighted tire is more likely to shake. You have linked brakes, I think, so I'd be interested to know what happens when you decelerate, and then touch the rear brake pedal, which will apply some front brake without touching the bars. It produces the weight shift without the steadying effect of your hands on the bar.

Lastly, in addition to checking that the front forks are straight, have you checked that they are aligned?

Dan B

 

[Matt]

good info Dan!

one more, are you torquing the axle, bouncing the front end to settle everything BEFORE tightening the pinch bolts at the bottom? trivial, but at this point it could be something little.

I still think head bearings are worn, in a way that won't be seen in a visual inspection. I'd replace them.

 

[cecilio64]

Yeah, sorry. V-Tec is a VFR model. I posted this in a VFR forum and copied it to here to get more ideas. Headshake happens during deceleration without braking.
Mechanic has checked swingarm, rotors, pads and pistons. Forks were lowered and I will talk with him tomorrow about the rear shock and maybe replacing the steering head bearings with roller bearings. We'll see what happens. And I really appreciate the input trying to figure this out. I don't have a whole lot of friends here yet to talk this over with and brainstorm, I do appreciate it.

 

[sobottka]

cecilio64;182034 wrote: Forks were lowered

as in you lowered the forks in the triples and raised the front end? having the front too low (either from geometry or too soft of springs) will cause this. if you raised the front, then i got nothin for ya set-up wise. dbarufaldi touched on something that makes sence, that is getting headshake from overloading the bike, but in this case, look at the front of the bike. a too softly sprung shock will not have these symptoms on decell, when more of the weight is on the front end.

 

[dbarufaldi]

sobottka;182059 wrote: as in you lowered the forks in the triples and raised the front end? having the front too low (either from geometry or too soft of springs) will cause this. if you raised the front, then i got nothin for ya set-up wise. dbarufaldi touched on something that makes sence, that is getting headshake from overloading the bike, but in this case, look at the front of the bike. a too softly sprung shock will not have these symptoms on decell, when more of the weight is on the front end.

I agree that raising the forks/lowering the front end makes the bike turn in more quickly, but will produce more headshake tendency than stock - that's the trade off, stability or quickness. That said, I raised my forks maybe 5 or 7mm, and don't have headshake without a big load.

How much change did you make in the forks?

Dan B

 

[cecilio64]

Yes, forks were lowered in the triples. I'm thinking the shock could be a good place to check, and one of the few not gone over yet. Got to look at it. Have ridden a lot of the 15,000 with my wife, Sonia. Running out of ideas and might just live with it and see if it gets worse and more "obvious". And I know, don't ride hands-off....

 

[cecilio64]

Raised the forks about 5mm. But all this was done after the problem started. Everything that was done so far has limited the headshake to between 83-78 kmh. So going in the right direction, just wish we could get rid of it completely.

 

[cecilio64]

Spent about 3 hours yesterday at the shop tweaking things, going out and trying them then coming back and talking with my mechanic. Probably did about 10-15 trips down and back the same stretch of road outside of town by the shop. Decided to live with the limited headshake for now. As I add preload (compressed the springs) the shake was shorter and less intense. But, I'm close to the limit now. I know from talking with Marshall that it's best to be somewhere in the middle of your adjustment range to let the spring work the way it's supposed to. So, I'm thinking that the springs are shot and too soft for me. 4 years of riding too soft springs coupled with them being compressed for the 2 and half months it took to ship the bike to Spain I think have toasted them. Because, when I turned the bike over to the shipper this wasn't happening and when I unpacked the bike here it started. The shake is not a problem, as long as you know it's there and keep your hands on the bars, no problem. Even hands off it's manageable. I picked up the bike today and told my mechanic I'd be back in a month or two for stiffer springs and to refresh the shock. Thanks to everyone for their insight and help. I really appreciate it:adore:

 

[daddyfriedrich]

My VF750S had exact same issue. found out the front forks were ever so slightly at different heights, which was binding the axle. Mine would wobble when going through long right hand sweepers. I have my forks exactly 38mm protruding above the top of the handlebars. i used a micrometer to measure, not a ruler. I also loosened the fork brace and "planked" the forks to make sure they weren't twisted. All my wobbles went away. Decel wobbles have a lot to do with trail. Hope this helps.