[speedypostman]

Hi forum!

Since the techs at the local Kawasaki dealer are now "spooked" by my bike, I figured that I would come to the people who really know their stuff.

I have a 1991 ex500. I bought it last year and when my buddy rode it home, he noticed that the front end would wobble crazily if you let go of the bars. We both figured it was due to the age and condition of the tires.

New set of tires later, the front end still wobbles if you let go of the bars when the bike is moving 30 mph +.

I took it to the shop to have them take a look at it. They replaced the fronnt wheel bearings, rebalanced the front wheel, checked the head bearings (all within spec), put a heavier weight oil in the front forks, removed and rebalanced the rear end, checked the rear swing arm bearings, tried a new tire on the front end, and 10 days later, had no clue what was causing the problem.

ANY thoughts? It rides fine at speed but only displays the wobble when presure is removed from the bars.

 

[ZX-2R]

TRY A FEW THINGS

First, Get a friend or two to observe, then stand over the bike not running and in neutral. lift UP on the bars to extend the forks then with the front brake on force the front end all the way down with just your full weight and have your friends observe.
Secondly,put it up on the centerstand, have someone set on the bike and hold the rear brake and handlebars and have someone try to push and pull the front tire forwards an backwards, then while the bars are being held firmly in place try to twist the wheel back and forth...all this looking for play. Weak forks, weak fork-springs...(I had a buddy witha problem similar to this that had just installed a brand new set of fork springs in his Yamaha YSR-50...only to find out after tearing it apart on the third time for our inspection that he in fact had only installed one of the two new fork springs. Ther ewas no way to tell with all of the static proceedures that it was the problem...only riding it showed that thre was something seriously wrong.) After we put the good spring in and went through the rest of the instructions again...and the problem was finally solved!!!)
Third, have the centerstand down and have a heavy prson lean all the way forward and twist/pull the rear tire back/forthand then twist (push-pull) from side to side...looking for loose suspension, worn out swing arm bushings, alignment...heck you could even find a bent wheel, or even worn cushions...(between sprocket and wheel).
Lastly, get on the bike and ride at the speed where this is happening and have another biker ride behind you, in front of you, even beside you if he/she has to, to see what is going on.

 

[Dave 96TA]

Another possibility is that the front or rear rotors are warped, causing unbalance. The smallest difference in weight can make a big difference on the road.

 

[speedypostman]

Thanks for the replies so far.

The 91 ex only has front rotors.

The shop said that the front and rear were to spec and were not able to find any play in either. I had read on another forum that it could be the rotor but how can you test for that?

When they balance a tire, do they balance it with the rotor on it?

If it is indeed the rotor, would it get worse with use? i.e. the hotter the rotor, the more wobble that it would create?

Thanks again!
Doug

 

[Dave 96TA]

Well the rotor is just metal, it can do all kinds of things at opposite ends of the temperature spectrum. If they're used a lot and get hot without a proper cooldown they can warp. If they're hot and you drive through some water or wash the bike, they could possibly warp. If they're bolted on too tight, the surface can deform. All kinds of reasons. You should be able to check for warpage by removing the rotor and laying it flat or spinning it and looking for deformation.

 

[Aikata]

They should balance the wheel with the rotor on because that's how the wheel will be spinning on the bike.

The only way I could see the rotor warping more is with consecutive excessively hard braking and no time to let the rotor cool down.

You say it only displays the wobble when pressure is removed from the bars? So, your typical riding style is to press on the bars?

What a strange thing for a motorcycle to do...

 

[ZX-2R]

heat

Most of the time heat will continue to warp the surface once it has started to warp. I had this problem on my car and my truck. Suggestion...Ride the heck out of it using the front brake only to yor driveway then have something like a jackstand handy and a scribe or a ruller nd put the bike aon the centerstand and rotate the wheel looking and checking for warp of the front brake rotor. On cars and trucks they are vented and can be turned no hte bike you may just have to replace it...but that would be cheaper than an accident an what ever it takes to get rid of the wobble... Also you can balance the tire on the front with it in place if you follow the Maintenance manual proceedures...just spin it and mark it several times...if it keeps settling to the same spot add weight and keep rotating till it no longer stops at the same place...you said that AFTER you put the new tire on this started..so it could be ballance but check it VERY carefully to make sure the bead is correctly centered on the rim...just 1/16" off and you will get bounce and wobble...

 

[jonesie619]

Hi forum!
...the front end still wobbles if you let go of the bars when the bike is moving 30 mph +.


ANY thoughts? It rides fine at speed but only displays the wobble when presure is removed from the bars.

Ummmm don't let go of the bars???

 

[fhqwhgads]

Speedypostman - any luck diagnosing your problem?

I posted a similar thread a couple weeks ago. Since then, I have checked just about everything you did: wheel balance, rim and rotor trueness, head bearings, swingarm bearings. I haven't replaced tires yet - I noticed this started happening AFTER I put on a fresh pair of Bridgestone BT-45s (which, by the way, have been excellent except for this wobble issue)...

I think this may be what's going on with both of our bikes:

http://www.mecc.unipd.it/~cos/DINAMOTO/vibrations/vibmode.html

Questions specifically for Speedypostman:
- What kind of tires are you running?
- What tire pressures are you running?

Questions for anyone who cares to answer:
- Have you had a similar issue on an EX500?
- Did you find any combination of tires (e.g. Bridgestone BT-45, Michelin Macadams, Metzeler ME330/ME550, etc.) and pressures that mitigated it?
- Did you find any other suspension changes (such as spring rate changes or fork oil levels) that made it better or worse?

 

[dustyattic]

Desperate times call for desperate measures. If you are desperate, here is an option. Personally, I would try it myself but I don't recommend it unless you are sure of your abilities.

If you are going mad wondering about the front brake rotor being warped, why not just remove it temporarily as a test? Remove the front wheel, take off the rotor and keep the caliper in place. Replace the front wheel and go. Make sure you dont squeeze the front brake lever because its likely your brake pistons will push right out and you will lose your brake fluid and the wheel will sling it all over the place, remove paint and taste funny. I wouldn't go into any kind of traffic and I wouldn't go fast. I estimate you will only have about 20% of your normal braking ability with the front brake disabled. I'm sure a lot of people will poo poo the idea as wreckless and stupid, but if you go slow in a safe, open area its a sure way to exclude the brake rotor as a problem.