New 80 mph wobble

[Guest Bigin]

After new Avons, progressive springs, and other maintenance items including swing arm bearing removal and service, I now have an 80 mph wobble that I never had before.

 

On a downhill it started as an oscillation then increased frequency before could react with the brakes but stopped when hauled down to 65 or so.

 

Cautiously ran up to 75 on another straight stretch but was uphill, and no sign of it to that point, but wasnt looking toy with that demon until rechecked everything on the bike.

 

The swingarm is as per manual assembly and torque values, and has no play, same with steering head bearings, front axle, rear axle etc.

 

This bike has never acted like this at speed until this maintenance project.

 

Always was a little saggy in the front with old springs and slighlty wallowing if pushed hard in turns but manageable, and had no high speed issues.

 

Now its on rails in the turns when pushed hard ( which leads me to believe everything is mechanically reinstalled), but top end is scary.That being sad, wondering if the increase ride height on the forks could cause this.

 

Like the Avons, cant be them, pretty sure anyway.

 

Any frame geometry techies out there that would know if raising the front end would potentially cause high speed wobble?

[Squeeze]

How much Pressure on the Avon's ?

[Guest Bigin]

Sheesh, should have checked the tires first. Told the tire man what to put in them and never double checked them.

 

Just did, the rear has 44, and the front has only 34 pounds, not sure about this particular brand but thats not enough in most, especially for a bike this weight and me on top of it = 1/2 ton on those 4 sqare inches.

 

Waisted you guys time except for another lesson about how important tire pressure can be.

 

Weather coming in here so wont be able to test ride for a while but thanks.

 

Will post again if that was not it but would be surprised if it not.

 

Thanks!!!

[oldandcrotchety]

Gee......I didn't even know there was anywhere here in Arkansas that you were allowed to go 80mph..........

[Guest tx2sturgis]

Just some generic suggestions...

 

Were the tires balanced? If so, did you lose a wheel weight? Tires maybe out of round? How about fork oil/air pressure...Have you serviced the neck bearings?

 

Maybe the swingarm pivots arent installed correctly...

 

Axles torqued properly?

 

Check everything.

 

 

[Guest Bigin]

Yeah did all that, except the first thing I should have checked-tire pressure. Was 34 pounds, should have had atleast 10 more in it. Will play with that and see if it improves. Thanks

[Guest Bigin]

Hey oldandcrotchety, havent you heard, it aint illegal if ya dont get caught, dont you know anythin about the law?

[Squeeze]

34 psi is 2.32 bar might be too less Pressure ... 40 might be a good Point to start with, adjusted on a cold Tire

 

 

Can the a elevated Ride Height cause a Wobble Scenario ?

 

Yes, it can. But i doubt that is the Problem you fighted with.

 

Just make sure you have the Steering Stem Bearings well adjusted and !!! the Pinch Bolts on the lower Fork Brace loose while adjusting the Bearing.

If the Pinch Bolts are tight during adjusting, you produce a tremendous Amount of preload on both upper and lower Yoke and this is NOT good.

 

Don't forget to bolt them down after the Bearing adjustment is done!

 

That all for now, i'm going to Bed.

[Guest tx2sturgis]

34?

 

Good age for a woman...bad pressure for a tire.

 

Not sure if that is low enough to cause a wobble though. Try around 36-40 on the front, 42 on the back.

 

 

[James Ardrey]

Suggested tire pressure on Avon venoms is 50# in back and 40# in front. Correct tire pressure is extremely important with the Avon venoms I understand. That is what I run and have had no problems.

[Venturous Randy]

Bigin, in the 90,000 miles I have put on my 83 with Bridgestones, Dunlops, Metzlers and Avons, with out a doubt, I enjoy the Avons the best....if I do not get much above 70 mph. The bike feels great to about 70 and the higher I go from there, the more squirlly the bike gets. A run to 100 mph scared the crap out of me. It seems that I am not alone with this concern with Avons on a 1st gen. After my 100mph run, I expressed my concern in the following post.

 

http://www.venturerider.org/forum/showthread.php?t=10048&highlight=wobble

 

The one thing that I did do that seemed to help my bike was to lower the rear tire pressure to about 43 psi from about 50 psi when hot. As I noted in that post, my wobble was a rear end wobble, not front end in any way. I wish I could tell you something to make you feel better, but I am afraid you have encountered the same concern that I have encountered

RandyA

[Rick Butler]

Bigin,

 

In my experience with 1st gen Ventures, a high speed decelleration wobble is almost always due to head bearings not being tight enough. The Yamaha procedure and specs will not get them tight enough. A good test is to put it on the centerstand and have someone hold down on the rear of the bike taking the front wheel off the ground. Center the wheel and gently push it off center. If it falls completely to the stops, it's too loose. You want it to move some, but quit before it hits the stops. And yes sometimes tire and pressures will have some effect, but it will always come back to the steering head bearings in the end.

 

And if you like to run fast (and straight) and be more stable, jack up the front and lower the rear. However in the Arkansas curves, you should let all the air out of the front and jack up the rear to quicken up the steering.

 

Hope this helps,

 

Rick

[Marcarl]

Another area of concern would be your motor mounts and frame bolts. When I went to remove my engine last fall I found all of them to be somewhat loose, not so loose as to be able to fall off or get lost, but loose enough to cause some play, and it wouldn't take much much for the scoot to notice that and start playing with you at 100 mph.

[GigaWhiskey]

I had washed out front springs and a sad set of tires. Then I had progressives and new matching Pirelli's installed. I do not know if that is what woke it up but I always had white knuckles at 80mph. That dreaded high speed oscillation/warble. The solid engine mounts darn near knocked it right out. I still got a little something but the white knuckles are now normal skin color at that speed.

[Guest Bigin]

Great info folks, thanks. Will check items suggested here.

 

Has anyone had a rubbing problem with the front Avon on the chrome mud guard bolts on the Gen 1?

 

Its slightly grooving the tire on one side from the bolt head that holds that chrome mudguard fender extension, and just touching the other side but not grooving yet, but it only has 34 pounds of air in it and needs a lot more.

 

Very tight fit, no adjustment on the fender that I know of.

[Marcarl]

Great info folks, thanks. Will check items suggested here.

 

Has anyone had a rubbing problem with the front Avon on the chrome mud guard bolts on the Gen 1?

 

Its slightly grooving the tire on one side from the bolt head that holds that chrome mudguard fender extension, and just touching the other side but not grooving yet, but it only has 34 pounds of air in it and needs a lot more.

 

Very tight fit, no adjustment on the fender that I know of.

Loosen the 4 bolts that hold the fender on at the forks, adjust the fender where it needs to be, and then while holding it, tighten the bolts. Also check the bolts that hold the fender extention on, don't just look at them but actually tighten them, fender extentions and car tires don't mix well.

[Guest Bigin]

Never realized could adjust that fender, will do thanks.

[MasterGuns]

Yes, I had to remove my chrome front fender splash guard when installing the Avon on the front. I saw that it was going to rub so I had no choice but to remove it. I even tried the stock black guard but the Avon is a little wider so I am just running without any fender extention on the front. Not a big deal; hardly noticeable.

[MasterGuns]

Loosen the 4 bolts that hold the fender on at the forks, adjust the fender where it needs to be, and then while holding it, tighten the bolts. Also check the bolts that hold the fender extention on, don't just look at them but actually tighten them, fender extentions and car tires don't mix well.

 

Heck, I wasn't aware the front fender could be adjusted. As soon as I can, I am will try it and see if I can remount the chrome extention. Thanks