Shaking/wobbling of frontend at deceleration, does yours to?

[robber57]

I already mentioned it in another post but the problem seems to be serious enough to make a special topic on it.

My SH has a problem which seems to be getting worse over time/km's .
If i let go of the handlebars at 70km/h(45 Mph) and let the bike decelerate at aprox 60-55 km/h (38-35 Mph) the handlebars/front end starts shaking/oscillating from left to right in violent way,the moment i grab the bars it will go away like nothing ever happened.

If i can manage to hold a videocam and still grasp the bars quickly enough i will try to make a video of the problem, but safety first , i will not risk my life for a video...

You might say: dont let go of the handlebars duh! , but every once in a while i want to do so to for instance adjust my helmet, close a zipper or something similar, its not that strange to do so imo.

The other comment may be: bring it to the dealer and he will fix it.
Well...
It's 4-5 years old so no warranty and in general; the amount and level of knowledge of dutch dealers is, to put it mildly CRAP.
Only exception are BMW dealers but they wont touch a honda and even a scooter to begin with.
Some telephone calls and explaining the problem and what i already tried to solve it to 2 nearby dealers revealed the following: ehhhhhmmmm..... - bring to us and we will see...
The last time i did such an act i ended up with a €700,- bill and still having a bad ignition.
The other dealer said " it comes with the type of bike (scooter), learn to life with it. ( like my signature)

When i got the bike it had some 600 km's (400 miles)on it and was like new and either i didnt noticed the problem or it was not there but as time and km/miles go by it seems to be getting worse.
The problem was only at aprox 60 km/h but now it will also go nuts at 30 km/h.

I already tried some variables like tire pressure,wheel balance(static),take of the mirrors and or luggage/top box, lowered rear spring tension,checked the steering stem bearings for free play/tolerance but to no avail.

My first question to fellow SH owners: would like to try and test if your bike has the same problem?
You might say " i appreciate my life and i am not in the mood to end mine-so screw you" but it is not that bad.
You just dont completly take your hands of the handle bars but place them very loosely around the bars, if you have the same problem the front end will at first start gently shivering at aprox 60 kmh-38 Mph and will get worse the longer you let it decelerate, if you firm your grasp on the bars it will disappear.

In the other post i already mentioned it: i am not the only one, on several fora (german/austrian/belgian) i read about the same problem,all these topics neber ended with a solution.
And its not only the/my SH which suffers the problem, i have head numerous bikes which had this problem and most of them i was able to solve it by trying other tires , changing the suspension or correcting steeringstem bearing tolerance.
Goldwings also can/may suffer from it: http://www.goldwingowners.com/forums/sh ... php?t=2917

Something which i found to be , at least curious if not suspicious is the short list of "ricambi" (spare parts) on the Italian honda website for the SH:
06430-GBJ-K20 1 freni Kit pat./gan.post. € 31,19 Brake pads front

06455-GCS-026 1 freni Kit pat./gan.ant. € 41,40 Brake pads rear

06911-KGF-020 1 telaio Cuscinetti di sterzo € 61,86 <<<Steering stem ball bearings)

17210-KGF-901 1 alimentazione Filtro aria € 15,16 air filter

22123-KRJ-900 1 trasmissione Rullini € 16,62 variator rolls

23100-KGG-911 1 trasmissione Cinghia € 38,29 belt

31500-KW3-505 1 elettrico Batteria GS € 74,99 battery cheap

31500-KW3-676 1 elettrico Batteria € 122,76 battery "maintenance free"

98059-58916 1 accensione Candela NGK € 10,32 sparkplug


Why o why are there steering stem ball bearings on the spareparts list? , normally , if well lubricated and adjusted stem bearings last a lifetime ....


Please post your results.....

[bigbird]

Check again, in no particular order, front tire wear pattern, front brake rotor to pad free play (there should be no grabbing), tire balance, steering head free play.
It may be worthwhile to actually remove the front wheel, check the wheel bearings, retorque the front fork pinch bolts, and install and balance a new front tire.
If you don't have a service manual, get one for the specs to do all this.

[Gripper]

Odd that you should post this problem just now. I have owned my SH150i now for just over 2 months and have about 900 km on it. I just noticed the same wobbling effect when releasing both hands from the handle bars. I didn't take now of the speed I was going but I will do next time and let you know. Of course, I'm still under warranty so I would very much appreciate knowing if there is something that the dealer should be doing to fix this inside the warranty period.

Keep me posted.
Paul

[robber57]

I have a service manual so checking on spec's is not the problem, the problem is that i cant find anything wrong.
The front tire is at 2500 km still like new, you have to look carefully to find wear, measuring with a caliper i dont see more then 0.1 maybe 0.2 mm wear so that is negligible , the rear tire has a little bit more wear but also negligible, the wear pattern, if any is even distributed, spinning the wheel it is as stable as a new tire gets no wobbling or other funny effects.
Wheel bearings are absolutely like new, no tolerance.

I am at the point of completely taking the front end apart but that is definitely not a job for a sunday afternoon, certainly if i find any problem for which i may need parts, so i first have to get my Derbi GP1 out of the garage and make it work.

The only thing i haven't done till now is have the front wheel dynamically balanced on a wheel balancing machine.
When i was racing i always did my own tires, replacement, cutting slicks to intermediate and static balancing and it has never failed me doing speeds up to 300 km/h so i cant imagine that there would be something wrong with it if the static balance is ok.
Problem to have a dynamic balance is the only shop capable is at 40 km's and the forecast just told me it's going to freeze and snow the next coming week...

[Wenzel4nv]

My Sh150i wobbles also. It has 2500 miles on it now and I just can't remember it having a wobble in the first 400 to 500 miles. I have been able to change the speed at which it begins to wobble by a little by changing the air pressure in the tires. I even changed tires. Not because of the wobble, but because I had another purpose in mind. It made no difference the wobble is still there.

When I asked my dealer about it ( his reply was " Don't let go of the handle bars".) I also removed my Givi windshield and made some test runs. No change, it still wobbled. I have read that many scooter and motorcycles have this fault, but I sure don"t remember having this problem on any of my other rides.

Have a good day riding

Wenzel4NV

[robber57]

Thanks Bigbird ,Gripper and Wenzel4nv for your input.

I have been reading up on the problem, thanks to the internet and all that knowledge just one click away.

If you care: http://www.associatepublisher.com/e/s/s ... wobble.htm , its a bit mathematical but if you read between the lines you get the point, there are also some great points on how to recognize or overcome the problem.

There seem to be two different problems regarding wobbling of the front wheel, one is called Shimmy and the other is called Death (speed) Wobble, i don't think any explanation on the last is needed in regards the effect.

It seems that Harley Davidson even had a class action suit in 2002 against them for speed wobble, i cant find the related article but you don't have to guess what probably happened to an (or several)unfortunate HD rider.

What the SH is suffering from is Shimmy and not speed wobble.

Death (speed)Wobble explained in 19 seconds: http://www.youtube.com/watch?v=LZ1srcQMa_
Other descriptions are tank slapper,(high) speed wobble.
It is the situation where the whole bike starts pivoting around a imaginary point somewhere around the center mass point of the bike, that is , in most cases, where the rider is sitting.
It often comes to this effect at high speeds and is therefore often lethal, i can remember a case in Holland where some 20-25 years ago suddenly riding a motorcycle became the new fashion and especially the "low rider" type became very popular, models like the Kawasaki Ltd 450 (due to the low saddle very popular amongst women) where imported in huge numbers even from the usa to follow demand:


Bikes like these are prone to this problem, your leaning way back, your torso is behind the center of mass, the relatively large front wheel dangles at the end of a 3 meter front fork which has no stability and can easily flex and most often the rider would put luggage or (even worse)saddle bags at the rear end which increases the problem.
A few people where killed in solo accidents and after a media campaign in all the motorcycle magazines the "low rider" model was out of grace.

However, the problem on the SH is Shimmy.
To explain what is happening the term "nutation" comes in and since it is difficult to explain: http://www.youtube.com/watch?v=hVKz9G3YXiw
Observe the circular motion the gyroscope makes when the weight is added and the guy pushes the gyro off center.
If you have ever held a spinning bicycle wheel at the axle in your hands you know what it is; if you try to move the spinning wheel gently you notice the gyroscopic effect, the wheel will resist to movement.
If you overdo it ,the axle ends( and the wheel) will start making a circular motion in your hands and you loose control and will have to let go of the spinning/nutating wheel.
Other view: To demonstrate to motion of a front wheel in a shimmy hold a bicycle wheel by the axle in your outstretched hands (not spinning) and move your hands in the motion of pedaling a miniature bike. If the wheel was spinning while you were doing this the wheel would be in nutation.


Well that at least explains what the problem is but doesn't give an answer how to solve it on the SH.
As i have read of numerous SH having the problem and most of them noticed already at low mileage i think wear most likely can be excluded as a source of the problem.

At this point, i find the steering stem ball bearing "issue" at the italian honda site (see topic start) the most likely regarding wear, if you over tighten a corner-contact bearing it will develop small pits in the bearing race and small dents on the balls and this can already occur after a few hundred miles.
That would not be wear but an assembly fault at the factory and its not the first time something like that happens.
Loosening the bearing after the damage is done is mostly useless, the pits and dents are there and don't go away and already may cause weaving of the front end which can easily progress to shimmy.
If there is no shimmy to begin with this problem usually shows itself as steering which pulls to one side if you let go of the handlebars, my SH didnt have this problem and after re-adjusting the stem i re-checked and this still didn't occur, but the simmy was still there.

I checked the service manual months ago and after reading the procedure to "adjust" the steering stem i was dead certain it was overtightened and this proved to be true, i had to unwind it for aprox 1/4 turn to get it right, i was quite certain it would solve the problem , but it didn't.
What is right? for angle-contact bearings the rule is; there has to be some free play/slack in order to let the steel balls rotate slowly so every time the bearing rotates the balls end up at a different location on the bearing race, in the ideal situation 0.00000000000001 mm is enough, practically it means you loosen up the bearing to the point you notice some (minimal)free play, its a tedious job and patience is required to do it right.
Also; it helps if you can do it without the whole cable bundle,frontwheel,fender and other stuff dragging on the steering stem.

For conical bearings the procedure is different; these absolutely require some tension to function properly and because they are under tension conical bearings have a slight dampening effect(which can eliminate/reduce shimmy), they also can manage more force and abuse.
Thats why often contact bearings are replaced by conical bearings but its not always possible, conical bearings are usually larger in size, if i can get hold of the measurements of the original sh bearings i will try to find if conical bearings can be fitted.

What i am actually hoping for is a sh owner still under warranty who will have it fixed at the dealer and post the result here , would save a lot of work and cost, the stem bearings are some 80 euro in holland and replacing them is a bunch off work, the 80 euro i can live with but loosing a saturday and sunday finding the problem is still there just doesn't make me eager to commence....