Chassis vibration over 120kmh

Hey folks,

I need to consult our experts, I have an odd vibration that Stacey developed on the last leg of this summer's 16-day tour of the UK. Stacey is a 98 5th-gen with about 22k miles on her.

The symptoms:
Over roughly 120kmh there is a pulsing, low-frequency vibration that increases in amplitude, but NOT in frequency, as speed increases from said 120kmh. In a poor attempt to describe it in writing, it's a "zzzZZZzzz...zzzZZZzzz...zzzZZZzzz..." and so on.

At 110kmh, it's not there. At 120kmh it's a "hmm, that's odd". At 140kmh I can see the mirrors following the vibration. At 150kmh the instrument panel also starts to shake (not extremely, but it's visible). I did not test it any further, for obvious reasons.

I can feel it in my feet and my hands, although it does not seem to come from the front end, I'll explain that in a bit. There is zero negative effect on braking and handling, as far as I've tested, it's simply there.



The tests thus far:
- Tire pressures, chain slack, proper brake function, steering head, wheel bearing smoothness, all ok.

- Forks are set to factory 9mm setting, fork oil was replaced last summer.

- As mentioned, various speeds, and the vibration changes in amplitude but NOT in frequency.

- No change with gears or engine speeds, I tried all the same speed ranges in 4, 5 and 6 with no difference.

- cleaned the brake rotor bobbins, this did improve braking a bit, but didn't affect the vibration.

- Followed the FSM for checking swing-arm and steering head bearings with the bike on the center stand, I can't feel anything the FSM says I should feel if there is a problem. The steering bearings swing butter smooth from side to side and have zero vertical play, and the swing arm is also rock solid.

- While riding, I put my hand on the triple tree and the forks, and did not feel any vibration at all coming thru those parts, it seems to come more thru the pegs and bars. I did my best to turn around and look down at the rear wheel as well, no shaking or vibration that I could see, although I couldn't really inspect closely.



Ideas:
- Wheel bearing smoothness was done with wheels mounted. Is it possible a bearing is failing, but isn't failed enough yet that I can feel it while rolling the wheel?

- Could this be a symptom of a failing rear shock? I know with our bikes these parts eventually wear out, and that would explain a pulsing and/or the comes-from-everywhere vibe, similar to a car with a hopping wheel caused by a dead shock.

- As with the wheel bearings, is it possible the steering bearings are starting to wear, but aren't yet worn enough to feel with the basic tests?

- Other ideas?



Thanks, folks, all input is appreciated.

 

Check steering head bearings.

 

I know it is counter intuitive, but have you looked at your chain to see if it has a pronounced tight spot?

I don't believe a failing shock could cause anything like you describe.

Most likely, have you lost a wheel balance weight?

 

at the speed (over 120) that it is noticeable, pull in the clutch to disengage the engine.
If it still is buzzy, I'd get the tyres rebalanced & then be looking at the head bearing.

 

My vote is for chain.
Rotate it to different spots and check chain slack.
Also check front and rear sprockets for wear or lose bolts.
If all ok check rear wheel bearings.
Steering head bearings won't do it, wheel balance would be a constant vibration that will change with road speed.
A shock could do it, but it would have to have virtually no oil and no damping whatsoever.

 

Thanks for the input so far, guys!

I'm away from home this week, but I'll have time Monday to check all these things. Some info per the posts:

- I did check the wheel weights, it looks like all are still attached, but that doesn't mean one hasn't fallen off and its glue spot been covered by road grime so I can't see it. I'd assume as mentioned that an out-of-balance wheel would be frequency dependent, but I'll check again anyway.

- A side question regarding the steering head bearings, as I mentioned before, i suppose it's possible they could be wearing, but not yet over the detectable limit with the FSM tests. If they're found to be loose, let's suppose by confirming with a torque wrench, can they be retorqued? Or is it at that point a replacement item, like a wheel bearing?

- Also, a dumb question in regard to the rear shock, I really have no idea what a dead one feels like, can anyone offer some insight in terms of riding feel? Stacey doesn't seem the least bit affected by the vibration, as I mentioned she rides just like she always has, and I like spirited riding. Maybe the rear shock is just fine.

More info on Monday, thanks again guys!

 

Ok, next update. I meant to check in LAST monday, but sometimes life makes plans without prior notice.

I checked the chain and sprockets today, and I don't want to be too optimistic yet, but I think we found the problem. As a side note, up til now, I've never had a motorcycle long enough to have to do a chain (or to have a problem with one), aside from adjusting slack.

First, the front sprocket was absolutely drowned in a lovely mix of chain oil and collected grime, I know now to add that basic cleaning to my maintenance schedule.

Second, as Cadbury and OZVFR mentioned, after cleaning I checked chain slack at many points, and sure as sh1t, I've got several millimeters of variation at various points. I don't fully understand how that's even possible, but if I had to guess, maybe some links just got so packed full of grime that they bound up...anyway...

As another point, and a newbie question for chain/sprocket work, I can move the front sprocket on its shaft a bit - is this normal? The bolt is tightened to spec (the rear sprocket bolts as well), but I can rock the front sprocket maybe half a millimeter, and shift it axially about the same amount along the output shaft. Hard to say exactly how far it moves, but it's plenty enough to see and hear.

So, I'll put on a new chain and sprockets and report back after testing.

Thanks again for the support, guys!!

 

Update. It isn't a chain issue. What a disappointment.

Installed the new chain & sprockets, tight spot is still there. This time (I'm an idiot for not thinking of this earlier) I noticed that the tight spot appears at a specific rotation of the rear wheel. It seems to be a bent axle, failing bearings, or both, but at this point I don't want to assume anything. So I'll get the rear axle torn down some time soon and keep digging. Any additional info?

Thanks, guys.

 

Update. Need some quick feedback, guys, I'm in the process of tearing the rear axle down. The service book (page 381) says "remove drive flange assembly" and "remove axle/brake disc assembly". I had to use a deadblow like a maniac to get the outer half of the drive flange off, and without a gear puller I've got pretty much zero chance of getting the inner half off cuz there's no contact surface for said deadblow. Does the manual simply forget to state that pressing tools are required for these steps? Or do I have an abnormal condition?

Thanks guys.

 

I know some people have had a real headache trying to do this.
No special tools are needed, but years of use and neglect make the assembly stick like shit to a blanket.
You just need to beat the crap out of it.

 

HAH!! That's a new one, thanks for the laugh :cool-new:

Thanks for the feedback, good to know I didn't just miss an obvious step. I'll pick up a couple pry bars so I can get between the surfaces. A bit of dry ice on the shaft may help, too.

On another slightly productive note, after getting the first half of the drive flange off with the shaft rolling freely, there are distinct crunchy noises coming from the bearings, and I can tilt the axle a bit in its housing, which I assume shouldn't happen even when partially disassembled.

 

Update, something is wrong, feedback welcome.

Spent too much time today fighting the drive flange, this thing might as well be welded in place. First we let some citric acid solution soak into the splines cuz there are heavy deposits on everything, then we had two big pry pars on two sides of the flange, and in parallel were hammering on it from various experimental angles with a deadblow. Not the slightest motion, and at some point stuff is gonna start breaking if we keep fighting it. Hopefully we haven't already warped the aluminum flange. See photos.





Anyway, if anyone has experience with this, please chime in, it has to come apart some how, and not breaking stuff would be preferable. What exactly is Honda's interpretation of "remove drive flange"?

Thanks, everyone.

 

Hey folks,

For anyone interested in how this issue has turned out, here's the newest update.

So the rear bearing assembly was definitely effed in some way, specifically how is still unknown becuz we never could get it apart. It took two people, a three-claw gear puller and a bench vice to get the chain drive flange off the axle, and it fought with screeching agony the entire way. We most certainly bent it pulling it off, but it didn't matter becuz the splines were visibly pitted and corroded. The only hydraulic press in all of effing Frankfurt (another story altogether) was at the local Honda dealer, he made a valiant attempt at pushing the axle out of the bearing hub and only succeeded in moving it about 3mm and then rolling the threads of the shaft nut over the axle. It's assumed that the inner splines and bearing surfaces look the same as the flange splines did. Over the winter I may get curious and use a dremel to cut the tabs off the bearing hub so I can slide it out the other side without having to remove the axle, it's toast anyway.

So I found a good used, complete 5th-gen swingarm on ebay and put it in. New chain & sprockets, new-used wheel bearings, and by coincidence a new rear tire becuz the existing one found a nail (the original was in good shape, most likely not part of the problem). I also checked the front wheel bearings, they're in good shape. Only the seals were a little worn, so I threw in new ones.

100% of the vibes through my feet and butt are gone, now I have a light pulsing vibe (maybe a third as strong as before) thru the bars over about 150kmh, which the local shop says is probably the front tire. It doesn't look severely worn, but there's some scalloping that they speculate could have been caused initially by the vibrations, and they're pretty convinced that when I replace the front tire the last of the vibes will be gone.

Thanks for the pointers thus far, folks, when the fresh rubber is on I'll report back.