HELP. Major head shake.

[JDS 07 S4Rs]

Ok, I thought I would post a problem I just found on a bike that I purchased the other day. I knwo that there is some great knowledge here.

I got a smoking good deal on a 06 ZX636R. Ins Write-off. Minimum damage. Small dent in frame.
Took it for a good workout the day I bought it. It "did" handle great. I put it through the gears, a few times. Redlining it to 5th gear. IT Goes.

Anywho. I strip the bike down. It is going to be another tracker (yes,, I am hooked on Track :-) It had Bridgestone Battleaxes on it. I replaced them with Michelin Power Race. Brand new, front & back. I also increased the front & back shock spring compression, & played with the Rebound & cmpression damping.

So, tonight I just got it all back together, take her out for a rip. & it develops the worst headshake I have encountered on a bike since 1974.
I was shifting from 2nd to 3rd,(front wheel was very light when it started with a small wiggle, & then violently started shaking,,holy "F", I thought I was a gonner.
I did it one more time, & it started to wiggle, so I backed off I put it in the garage. It was just getting dark(no lights on bike)


It cant be the Michelins, can it ? I just read another thread. "Hypurone" had a similiar problem on his S4RS with Michelins.

Things I have changed. Knocked off over 20 Lbs in useless cosmetics. New tires, played with suspension.

Any sugestions,, anybody ?

[derby]

 I also increased the front & back shock spring compression, & played with the Rebound & cmpression damping.

so you just willy nilly started turning knobs?

did you change the geometry when you put it back together? raise the rear? lower the front?

[darylbowden]

Any sugestions,, anybody ?

Yeah, don't change settings if you don't know what they do.

Take it to your local suspension guru and have them sort it out (preferably someone familiar with the 636), none of us are going to be able to give you answer that is going to solve that problem - at least not over the web.

The tires, while they may change the geometry slightly, should not be the sole cause for massive headshake.

[JDS 07 S4Rs]

I know what the knobs do. & I set them each identical on both forks. It wasnt a track bike when I bought it. There is a total 2.5 turns on rebound, mine are set 1 full turn out. Same on compression damping

No, I never changed the geometry.

NOTE: I just did a little investagating. There are no weights on either of the rims, wtf. This is a 1st. Has anyone ever had tires & rims that didnt need weights ? How the "F" could he not balance the tires,,,arrrr

U guys make me laugh, do either of you do any wrench twisting?. Dont take that the wrong way. I just like to play. My suspension was bottoming on the front under braking. What would U do? Adjust, or take it to the Guru ?
If I would have known I was almost going to get tossed, I would have taken it to a Guru,, "F' that was scary.
Anywho, I will look into these missing weights.

[darylbowden]

I know what the knobs do. & I set them each identical on both forks. It wasnt a track bike when I bought it. There is a total 2.5 turns on rebound, mine are set 1 full turn out. Same on compression damping

No, I never changed the geometry.

NOTE: I just did a little investagating. There are no weights on either of the rims, wtf. This is a 1st. Has anyone ever had tires & rims that didnt need weights ? How the "F" could he not balance the tires,,,arrrr

U guys make me laugh, do either of you do any wrench twisting?. Dont take that the wrong way. I just like to play. My suspension was bottoming on the front under braking. What would U do? Adjust, or take it to the Guru ?
If I would have known I was almost going to get tossed, I would have taken it to a Guru,, "F' that was scary.
Anywho, I will look into these missing weights.

Sometimes wheels don't need weights, not often, but occasionally.

As for my suspension, no I don't make the beast with two backs with it 'cause I don't know enough about how to properly tune it.  I have a good relationship with my track mechanic and he takes my input and then makes the necessary tweaks.

Anyhow, if the geometry is mostly the same (aside from the new tires I mean) and you know enough about suspension that you didn't mess up anything, then I would say the wheel weights are a likely culprit.

[sqweak]

they've both raced.  i'll let you figure out if they know what they're talking about or not.

Take it to guru.  Just like daryl and gm2 told you the last dozen times you fiddled with suspension and couldn't figure out what was wrong.

[tufty]

Fyi, you changed the geometry when you put the Michelins on.

It sounds to me that in your zeal to change the suspension you did something combined with the new tires that it doesn't like. Get the suspenders set up by a pro.

[Jester]

There are no weights on either of the rims, wtf. This is a 1st. Has anyone ever had tires & rims that didnt need weights ? How the "F" could he not balance the tires,,,arrrr

One of the rims on my Monster is perfectly balanced fwiw.  Happens, but like Daryl said, not often.

[JDS 07 S4Rs]

I know the guys know what they are talking about. Thats why I posted on here. But, I am not a kid that just picked up his new toy. Hmmm, ok. ya I am a kid, but a old one

The Michelins can change the Geometry !!!!,,,,,,hmmm. How so. Are they taller ? I never touched the Compression or rebound on the back shock. But I did increase the spring tension. Baised on sag. If the Mich's are taller, & I put more height on the rear, in theory,I could have drasticly changed the geometry, hmmm.

One a side note. It may be a good thing that the Kawi doesnt have a height adjuster 

I have another hr to play B4 the guy who install the tires opens his shop. I need to find out about these weights. This time full leathers go on.

[derby]

1) tire changes can result in geometry changes due to the difference in rolling height.

2) if you only touched compression/rebound on the front, it's possible the front and rear are "out of balance".

3) if you increased the preload on the rear, you possibly increased the rear ride-height, changing the geometry. more rear ride height = steeper steering angle = twitchier bike.

now, if it was fine before, what changed?

how fresh is the suspension? old oil? are the springs correct for you? it could just be some old, worn out suspension that needs a rebuild, or you could be over-preloading the bits to get to your (compromised) sag settings. or both.

[JDS 07 S4Rs]

Well. I survived. I changed the Rear spring tension back to where it was. &. "No more headshacks" Just a twitch/wiggle shifting from 2nd - 3rd at redline. Thats what initiated the headshakes last night. I think my riding position may have factored into this equation. I was sitting to far forward,, maybe ?

Hard for me to grasp that such small adjustments make such a big difference.

Ok guys, one of these days I will get the bike set by a pro. Which likely means a dif rear shock, & dif springs in my forks.

Cheers   

[derby]

Hard for me to grasp that such small adjustments make such a big difference.

there's a reason they measure these changes in millimeters.

Ok guys, one of these days I will get the bike set by a pro. Which likely means a dif rear shock, & dif springs in my forks.

on the shock, you may be able to get away proper springs and a rebuild w/ fresh oil... often the biggest issue with those is the crap fluid the put in at the factory that's basically worthless after it gets hot.

[ducpainter]

Well. I survived. I changed the Rear spring tension back to where it was. &. "No more headshacks" Just a twitch/wiggle shifting from 2nd - 3rd at redline. Thats what initiated the headshakes last night. I think my riding position may have factored into this equation. I was sitting to far forward,, maybe ?

Hard for me to grasp that such small adjustments make such a big difference.

Ok guys, one of these days I will get the bike set by a pro. Which likely means a dif rear shock, & dif springs in my forks.

Cheers   

never heard of a forward riding position inducing headshake.

[myssrhl]

If during a gear change try "GP" pattern...

A lot less "up set"

[gm2]