High speed wobble... :O

Dear KZ Riders ,

For the first time on a track test (for fun) when I've reached over 115 mph until top speed 130 mph. The steering started to wobble but not a tank slapper, slowly waving.

At 60 mph, i noticed its easy to get it wobble just by pushing a gently each side (less than 1/4 inch) alternately ... could this because bad steering bearing? I don't feel any play at all in the steering that's why I'm asking?

EDIT: feeling like it's too sensitive (steering) over 60 mph... or maybe it's just me :laugh:

regards,
laurent

I'd check things out in this order:

1. Tires (they can look good, be mounted & balanced right, and have correct pressure and still cause high speed wobble - this happened to me).

2. Swingarm pivot bushing/bearing play (lift rear wheel off ground; disconnect shocks; see if you can twist swingarm at all - you should not be able to)

3. Steering stem bearings (lift front wheel off ground and see if there is any fore and aft play - too lose; also see if handlebars can flop to either side with zero resistance - too lose; there should be only very slight resistance but they should not be sloppy

4. Rear shocks

Ed

Double posted - thanks Comcast.

I copied this from a post from Jeff Saunders(owner of Z1 enterprises)

Motorcycle Wobble Causes

There's a LONG list of potential area that can cause this.

These are not in any particular order
Wheel bearings
Steering bearings - repack grease, check tightness
Swing arm bushings/sleeves/bearings - replace is worn, repack grease
Fork springs aging - check spring length
Unequal fork oil - if seals leak, then your damping can be ineffective
Rear shocks aging, damper leaks - if you have oil leaking from the seals, the damping is toast.
Worn Tires/Mismatched tires/tire pressures/wrong size tires
Wheel alignment - don't trust the chain adjusters - I visually align the wheels.
Bent rims/broken spokes - get the wheels off the ground and spin them - check for runout / damage
Front disc warped - check for runout

Steering & swing arm bearings are very common problems, but so are tire issues (pressure/mismatch) and wheel alignment.

thanks guy, i will check these

btw, i think the steering bearing is taper on the KZ750-R1 1982 (GPZ) ... do i need special tools to change this?

thank you very much


regards,
laurent

I had wooble but reduced it by adding a fork brace from .. to fast from the past,,, they have a full range of fork braces

I had wooble but reduced it by adding a fork brace from .. to fast from the past,,, they have a full range of fork braces

Isn't the second purpose of the wheel guard to act as a fork brace ?

Thanks for the site but unfortunately they don't have a fork brace for my model KZ750-R1

regards,
laurent

Thanks for the site but unfortunately they don't have a fork brace for my model KZ750-R1

Nevermind found them it was on another page

www.fastfromthepast.com/servlet/the-556/...asaki-KZ750GP/Detail

When money flows again, this and a new set of rear shock are a must!

New set of tires + maybe steering bearing and swingarm but i need to check like 650ed told me


regards,
laurent

I had a similar experience in my newly build that as you thought was steering head... Turned out to be something entirely different...

1) Raise the front end so front tire can spin freely.
2) Remove front fender for optimum view over top of tire/rotor.
3) While standing directly above tire/rotor, spin and see if either is warped....

Ah, sonsabitch there it was, rotors were rubbing on warped spots...

Just a thought...

What you describe is more commonly called a weave, and on the GPZ750's the most common cause is overtightened steering head bearings (tapered bearings).

Interesting tidbit about a weave.

One of the cycle mags decided to do a top speed shootout to determine the fasted street bike. They fully expected Terry Kizer's (Mr Turbo) turbocharged ZX11 to win, but had to shut it down a little over 200 mph because they couldn't keep it in a 12 foot wide lane at that speed due to weave.

That bike had been on well over 100 (800 comes to mind, but not sure) dyno pulls as a development mule for the ZX11 Turbo kit, and the frame was tweaked. At least that was their determination as to the cause of the weave.

Boggles the mind :woohoo:

i used to get into a tank slapper at over 100mph. pretty scary stuff. :woohoo: it turned out to be the front tire out of balance.
personally, i would put the fork brace on the very bottom of my wish list. it would only rely be a necessity ,for a track bike. as for aiding a wobble, i would rather get to the source of the wobble than try to tame it.

I had a similar experience in my newly build that as you thought was steering head... Turned out to be something entirely different...

1) Raise the front end so front tire can spin freely.
2) Remove front fender for optimum view over top of tire/rotor.
3) While standing directly above tire/rotor, spin and see if either is warped....

Ah, sonsabitch there it was, rotors were rubbing on warped spots...

Just a thought..

Good tip OMR thanks, i have a dial indicator i will check the run-out with that. My eyes, even if they are young play tricks on me sometimes

What you describe is more commonly called a weave, and on the GPZ750's the most common cause is overtightened steering head bearings (tapered bearings).

Thanks stell weaving is the correct term! However that doesn't make sense logically! I'm not saying that you are wrong but would be a loose steering easier to vibrate than a overtightened one thus creating waves?


My are tires are due, they are Dunlop GT501. I think the date code say its made in 2001 :ohmy:

regards,
laurent