head shake!

[il_ragazzo]

ive swapped out for a gsxr 750 front end and noticed that while im accelerating at high speed ~80-90 the bike becomes less stable. but if im decelerating from ~90-80 its more stable. it's not a head shake quite yet but if i was to get on the throttle then hit a bump it will take it longer to work out the shake. if i hit a bump while braking then notting really happens and the shake is worked out imideatly.

my hypothosis.
1. when accelerating im moveing the weight off of the forks which is cause a slight geometry problem. This theory is reinforced by the fact that the bike is more stable when braking. I.E when more weight is on the forks.

corrective action would be to lower the front and raise the tail.

opinions? options to correct?

[squiggy]

Sounds like a definite steering geometry alteration.

Did you measure prior to installation the fork differences between the Kat's forks and the GSX-R's forks? I'm curious as to the differences.

So far I've measured and concluded is that the Kawi ZX-14 forks would be the closest in length to my forks so that the geometry would be as close as posible.

An advantage the Post's Kats have is the electronic VSS, no speedo cable to consider.

[Mikey Dank]

could it also be a damping issue? I know with front suspension stability there are two terms, don't remember both, I think one was rebound damping, can't remember the other. One is the force applied to the front tire for the tire to return to the ground after a bump and the other is the force required to lift the front tire towards the bike...idk, just a thought...

[suzukiray]

Do you have the bearing preload CORRECT on the steering head bearings? Ray.

[tobias]

lotta questions is all i have. is the tire/rim balanced? what year did it come off of , maybe that was an issue with the gsxr that year, um tire condition air pressure, are all you torques to spec, and do you get head shake when no hands up front?

[il_ragazzo]

all good question... the 94 750 gsxr forks are in the steering head CORRECTLY, and every thing is torqued down properly. tires are still in great shape and with correct psi. when i take my hands off the bars the bike is quite stable because it is decelerating. i haven't felt the bike shake its head, but when accelerating it feels like it could if induced properly. especialy if i have a passenger. the passenger would increase the rearward weight and reduce weight in the front making it even harder for the bike to work out the unstableness.

[The CyberPoet]

Questions:
(A) Did you change the fork springs on the GSXR forks to make up for the Kat's extra weight?
(B) Did you rebuild the forks (oil levels, seals) before installing them?
(C) What's the gearing on your bike (stock sprockets?)
(D) How old is the tire?

Cheers
=-= The CyberPoet

[il_ragazzo]

the 94 kat and the 94 gsxr are only 5lbs different in weight. the 5lbs of extra weight can be taken from my back pack.

i rebuilt the the forks before i installed them. no leaks nothing that i saw to be concerned with.

im running 15,47 on the pre 600 which is -1f +2r

the tires are in decent condition only 3-4k miles on them . i was checking for cupping but i couldn't find anything visual. (though it may be in the earlier stages.)
my last tire (Dunlap bias) cupped and made a horrible head shake problem for me... then i bought these metlezers and i love them.

could it be that weight distubution is the cause off my high speed instablity?
it never had a head shake. it just feels like it wants to.
-B12 shock raised the rear about 2 inches.
-gsxr clipons put more weight on the bar by lowering my riding posture by 3"

i do beleive kwebbel used a steering damper for his kat with roughly the same mods because he raised the rear of the bike. so if i lower the rear i should solve this .....kwebbel also moded the rear suspention. so that may be the cause of why he would have to buy a steering damper.

personally its not problem enough to me justify buying a damper becasue i feel i can find the right suspention setting to work it out. especially considering that i would only encounter the problem at extremly high speed if induced my myself or uneven pavement. (which i shouldn't be speeding on in the first place.)

some times i think aloud.... ^ thats one of those times... oh im now 23... 23 enigma time...

[The CyberPoet]

the 94 kat and the 94 gsxr are only 5lbs different in weight. the 5lbs of extra weight can be taken from my back pack.

Potentially flawed logic. Although the weights may be within 5 lbs of each other, the weight-distribution probably is far different (with the GSXR running a longer swingarm and putting far more of it's weight on the rear wheel). That could lead to a situation of the forks being overloaded on the Kat; you'll know by the degree of brake dive on hard deceleration.
BUT since the front suspension is only misbehaving while under acceleration (and my guess based on your gear choices, somewhere by peak torque), this shouldn't be the basis for the headshake issue.

im running 15,47 on the pre 600 which is -1f +2r

It's stock front. No Kat 600 or 750 shipped with a 16 tooth front.

the tires are in decent condition only 3-4k miles on them . i was checking for cupping but i couldn't find anything visual. (though it may be in the earlier stages.)
my last tire (Dunlap bias) cupped and made a horrible head shake problem for me... then i bought these metlezers and i love them.

The symptoms don't appear to be the tires either, or else it would occur while at neutral throttle -- you say it's only happening while accelerating.

could it be that weight distubution is the cause off my high speed instablity?
it never had a head shake. it just feels like it wants to.
-B12 shock raised the rear about 2 inches.
-gsxr clipons put more weight on the bar by lowering my riding posture by 3"

Raising the rear changes the geometry, making the angle of the forks steeper, which induces extra instability (or more nimbleness; it's all point-of-view on that concept). If the forks are shorter in length (or higher in the triple-trees), that would exacerbate the problem. The clip-ons would tend to amplify any instability because of your riding position and how it changes the leverage through your back (think Chi, as in Tai Chi).

i do beleive kwebbel used a steering damper for his kat with roughly the same mods because he raised the rear of the bike. so if i lower the rear i should solve this .....kwebbel also moded the rear suspention. so that may be the cause of why he would have to buy a steering damper.

I concur that lowering the rear downwards or installing a damper is called for. The last thing in the universe you want is the bike's front traction to go light at peak torque, which in theory could happen at almost any speed, depending on gear choice at the moment (because it's controlled by the engine's RPMs and throttle manipulation, not by the actual MPH).

Cheers
=-= The CyberPoet

[il_ragazzo]

ok ima start tinkering with it this weekend. raising clip ons and lowering rear. i think the girlfriend wants me to lower it anyways... she's alil short.
how much do u think i should lower it?

oh good call on on the forks. i hadn't thought of it like that...

oops, yeah meant +1F+2R

[The CyberPoet]

how much do u think i should lower it?

Until the head-shake disappears at all RPM's/all speeds...

Cheers
=-= The CyberPoet

[erok011]

what does it mean if when you take your hamds off the bars there is a small shimmy only sometimes?

[The CyberPoet]

what does it mean if when you take your hamds off the bars there is a small shimmy only sometimes?

Then you have a small amount of headshake only sometimes.
The rate it shakes at, the speed & RPM you're going factor into the reasons.

Cheers
=-= The CyberPoet