"Bad" noises from the shaft drive on my GS650G Katana

[Jmavatar]

Hi guys!! Greatings from Switzerland!!

Since I bought the bike(a couple of months ago) I noticed some vibrations/noises on the bike at 4500rpms(mostly in 2nd and 3rd gear).
Then I heard that those vibrations are quite normal on those engines. But know the noise is higher. And now I realized that the noises came from the shaft drive.

The noises appear always between 4200 and 4700 rpms. Is like a steel piece is moving free inside the shaft drive. But why just at those rpms?

The bike change gears perfectly and very smooth. But when I accelerate and run over those 4500rpms, the noise appears.

Any tip? Solution?? Idea???

Thanks a lot!!!

[TheCafeKid]

First, double check that your final drive oil is at the proper level, and clean and fresh. Then, if that doesnt seem to have anything to do with it, remove the wheel and have a look at the splines inside the hub, also the "pumpkin" splines, you may also have to check the drive shaft, ujoint and, depending on how far up the noise is coming from, the drive and driven gears. The rear hub spline going out is a common issue on the mid 81-and on 850-1100G/GL but I hadnt heard of it happening on a 650. I suppose its possible.

[Dave8338]

Are you sure that it isn't a harmonic transfer from the engine to the drive shaft? Have you synched the carbs? It makes a HUGE difference in vibrations, especially those that are hard to track down.

[Jmavatar]

Thanks guys!!

The carbs were cleaned and syncronised. Also new oil in engine and in shaft.

The extrange thing is that those metalic noises appear just around 4500rpm. Allways the same. Most ofen in 2nd and 3rd gear. This is what it make the thing tricky.

And I am 99% sure the noise came from the shaft drive. The noise is like a metallic pice just start to move in the drive shaft cage at 4500rpms. And after those rpms it doesen't move more.

So extrange is this??

[Dogma]

What else in the general area of the shaft drive might be vibrating? Something near the fuse panel, or maybe one of the stands banging on the frame? The fact that it's at specific revs, and not specific speeds makes me think it can't be the shaft drive.

[psyguy]

you are probably referring to the noise while driving, not stationary?
if so, it can be that the noise is happening in all gears but you can't hear it due to the engine/wind noise while riding in other gears.

i wouldn' be surprised if it WASN'T the shaft drive but just some resonance or engine noise (especially as it is related to RPMs not speed).

but if you want to inspect the shaft, etc, follow the cafe kid's advice

[Jmavatar]

Hello again after holidays!

Thanks a lot guys for your tips.

Y spend one evening with the bike and I made some tests. Now, it seems that this metalic noise came from one cilinder of the right side(if I disconnect the spark plug) it doesen't sound.

Finally I can afirm that this noise happen in all the gears, even without any gear. Bur ALWAYS at 4200-4500rpms. In the other rpms not noises at all. Extrange, isn't it??

Anybody knows what to do??


Thanks a lot!!!


V'sssssssss

[gs_schmuck]

Hmmmm, could be a bad bearing on that piston. Bummer. If you're lucky it's only a bad cam journal.






.

[mike_of_bbg]

Unplugging which cylinder makes the noise go away? What kind of noise is it? Metallic you said. Knocking? Grinding? Rattling? Pinging?

My cam chain tensioner rattles pretty well when the bike is cold from 2500-4500 and the sound is pretty bad. Just putting a finger on the knob (not turning it) makes the sounds stop. Then again, I doubt that would stop by unplugging a single cylinder. Something to look at though.

I'd try running a compression test, then pull the valve cover and check the clearances and conditions there. Yours is an 82?

[psyguy]

well, you've traveled some distance to diagnose the noise first from the shaft now to a cylinder

if the noise is clearly related to a single cylinder then i would suspect a bad conrod bearing but i think what you would hear would be a KNOCKING metallic noise and would also be apparent at lower rpms and the sound would speed up as you increase the rpms.
try confirming if this is hapening at all.

the only other thing i can think of that would give such symptoms, as i said earlier, would be a resonance - and if related to only 1 cylinder - i can only suspect a loose exhaust pipe flange bolts/nuts.

anything to do with the valves or cams i think you would hear all the time even if you take any plug out.

keep us informed

[Jmavatar]

Hi guys! Thaks a lot for thw tips!

The bike is from 82/83.

But is not easy to detect where the sound came from, because also in the back of the bike(near the shaft drive) the noise is quite high(it seems the noise travel from the motor to the back side through the exhausts)

And is a really disgusting noise, probably a "Rattling" noise. Also it produce a vibration in all the bike. If needed I can try to upload a sound record of it. And the noise came (99%) from the cylinder nr. 4. It disappear once I disconnect this cylinder plug. I am sure that the noise take place only in those rpms. Sure.

The noise happen either with the motor cold or warm(in this case the noise is higher). And if I pass through those 4200-4500rpms accelerating a lot, I can't hear any noise or vibration.

If the problem is the cylinder bearing... this will cost me a lot of money in the garage! What a pity. In this case I should change this bearing or shouldn't became into a bigger problem??

I forgot to mention that the noise is (or at least this is what it seems) higher since I carburated the bike and adjusted the iddle needle. The iddle works perfect at 1000rpms.

[psyguy]

it produce a vibration in all the bike.

that sound bad as about the only thing that i can think of that could cause the whole bike to vibrate (especially from only one cylinder) would be a bad conrod bearing.

were you able to tell if the noise "speeds up" as you go from 4200 to 4500 rpms?

it may also be that the other bearings on the crankshaft are not that good but that at 4500 rpm they come into a resonance with each other and accentuate the problem. (this would actually be my best guess...)

now, i'm not an expert and would hate to see you take the engine appart and find nothing wrong with the conrod bearings

what do you guys think???

[49er]

Hi guys! Thaks a lot for thw tips!

The bike is from 82/83.

But is not easy to detect where the sound came from, because also in the back of the bike(near the shaft drive) the noise is quite high(it seems the noise travel from the motor to the back side through the exhausts)

And is a really disgusting noise, probably a "Rattling" noise. Also it produce a vibration in all the bike. If needed I can try to upload a sound record of it. And the noise came (99%) from the cylinder nr. 4. It disappear once I disconnect this cylinder plug. I am sure that the noise take place only in those rpms. Sure.

The noise happen either with the motor cold or warm(in this case the noise is higher). And if I pass through those 4200-4500rpms accelerating a lot, I can't hear any noise or vibration.

If the problem is the cylinder bearing... this will cost me a lot of money in the garage! What a pity. In this case I should change this bearing or shouldn't became into a bigger problem??

I forgot to mention that the noise is (or at least this is what it seems) higher since I carburated the bike and adjusted the iddle needle. The iddle works perfect at 1000rpms.

I doubt that it's a bad big end. A failing big end bearing will be heard when the engine is under load, throughout the rev range. During light acceleration and decel, it won't be audible. The fact that the noise disappears when #4 plug lead is disconnected would appear to indicate that the problem is related to that cylinder. However, you shouldn't have noticed an extreme vibration, if it was a big end failing.

My initial diagnosis from your first post was that the universal on the drive shaft was suspect. It could even have been the mount bolts at the flange coming loose. The easy way to eliminate these possibilities is to check the amount of backlash present at the rear wheel. If it is more than 1" movement, you need to investigate further.

If the backlash checks out ok, leave the spark plug lead on #4 and place a long screw driver against the cylinder and your ear to listen for knocking sounds when the engine is reved through that range. If you can't hear it there, place the screwdriver on the engine case at #4 and listen. If it is a big end, you will hear it pain as day.

I still think that the vibration you mention, is more likely from the drive shaft.
When you disconnected the spark plug, besides the noise disappearing, did the vibration go too? If it did, then a bad big end is more likely.

[BassCliff]

Hi,

I had a funny rattling noise on my bike for a while. It was always around 3400 rpm. I rode like that for a week, touching various parts of my bike to see if I could stop the rattle. Finally I looked under my tank and saw one of the horns had come loose from its mounting and was flopping around on the valve cover. I found a new nut and bolt, problem solved.


Thank you for your indulgence,

BassCliff

[SqDancerLynn1]

If it was a bearing it would get louder as the rpm increased,