5k rpm vibration

My 82 xj650j feels like its vibrating accelerating past and decelerating at the 5k mark. I know there's been some previous talk about this but I was wondering if anyone found a for sure solution to fix this problem.

 

Carb synchrinization eliminates most of it. The buzz is a nature-of-the-beast thing.

 

I recently added bar weights to my bike, helps a lot with vibrations, the engine is solid mounted so.... Yeah

 

Also, just to ask, at 5000 in top ger on the highway? Or in all gears, if only on the highway it could be a harmonic vibration if the bike has a lot of highway miles at roughly that RPM not the motor.

 

It vibrates in all gears at 5k. It seems to go away once the rpm's are above 5k but vibrates on decelerating and getting down to 5k also. It didn't Used to do it before I broke an exhaust manifold bolt. And removed the exhaust and re-installed it.

 

I appreciate all the help

 

Maybe the exhaust is touching the frame somewhere and causing it... Idk?

 

Other than that you randomly picked up a fuelling issue at the same time

 

I will definitely check the exhaust and let you know. It seems like I caused it somehow. I never had this issue before I broke the exhaust manifold bolt and removed the exhaust pipes. Ive removed the pipes before and reinstalled them with no issues. i could run the bike pretty if hard if I wanted too without any issues.

 

What exactly are bar weights? Im not familiar with them.

 

The 5k ‘harmonic buzz’ is a documented phenomena- not a vibration as much as a sensation. I feel it in my left foot peg the most.

 

I guess you could call it a buzz but it sure feels like s vibration. It resonates thru the whole bike and thru your body.

 

You guys are the experts I'm new to this bike. So I appreciate what ever info you have to offer.

 

I'll check back gotta work tomorrow.

 

Bar weights are long shafts of steel with rubber plugs not the ends just bigger than the metal that slide into your handlebars, some (like mine) also have 1 or 2 o rings in the middle.
The idea is that when the bars try to vibrate and cause carpal-tunnel syndrome instantly, the weights try to, and seem to very well, counteract that vibration and minimize it.
I'm not a scientist for the expaination, but they did seem to help.

 

Anyone wants to buy me a set of grips, I'll cut em off and post a picture of the weight... Lol!

 

I was looking at my bars, stock grips... could I cut a hole in the end and mount the weights or does it require new grips?

Just a comment... I always thought of this as "My bike vibrates at 65mph but it's surprisingly not as bad above that". I wasn't even thinking of engine RPM and thought it was just part of having an old bike, tire balancing, etc. I just watched the tach on my way into work and sure enough it's 5K. In large propulsion diesels and gas and steam turbines (my background) there's something called "barred speed". It's the speed at which the engine gets in the harmonics zone and will eventually shake itself to bits if you try and operate it there. The design engineer's job is to ensure this happens outside any range that the machine could be operated at in doing it's job, and it's the operator's job to transition through this speed as quickly as practical.

Since my speedo redline is 55 mph as was the speed limit in 82, I just wonder if the design guys took some liberties and figured "65mph is fine as they are not supposed to be operating there anyway..."

Things I'm distracted with on a Saturday at my desk.....

 

The cap at the end of the grip holds the weights in, you have to replace grips, or I guess a blob of silicone, but that's ugly.
Emgo sells a foam type soft grip for like $15 also reduces vibration a bit, plus they have cool gold Eagles on the chrome end caps!

 

I Won't get a chance to look at possible issues that could be causing my problem until sunday night after work. I was just trying to compile as much info as possible based on everyone's experience and expertise to help me in solving my problem. The bar weights are interesting. The strange thing is I didn't have any vibration or buzz at any rpm before I broke a manifold bolt.

 

The Seca 750 bars have a steel plug welded into the right end of them. It's heavy enough to act as a bar end weight, so you'll only need one weight for the left side.
I filled my (aftermarket) bars with butylene rubber caulk to dampen the vibration, which is something you can do to the stock bars. Use a lenght of vinyl tubing so you can start the fill on one end and retract the tubing as you go to make sure that all of the bar is filled.

 

Well I removed the exhaust and reinstalled it making sure everything was tight and secure I even added new bushing to the rear exhaust mounts. I also added new bushings to the fins of the engine. It seemed to help but the buzz is still there about 5k. I guess my next option is too check the valves??? Any thought?

 

Did you do this already?

 

I was wondering about carbs I noticed it running a little different. I haven't synced them yet because it was running so good and the bike would come unleashed at 6k.
It seems strange that I never had vibration or a buzz before I broke an exhaust bolt? One of the nuts came loose and the other one must have broke due to pressure and stress.

 

The carbs can come out of synchronization over time. It's worth having a look.
Even a bit out of synch enhances the buzz, but won't affect performance enough to notice.

 

Ill have to try that I've never synced carbs before ill have to locate some gauges and try it any advice on syncing them? It doesn't sound too hard to do.

 

Duuuuuude.... Do It!
Big difference.

Believe there is a good rundown in the DIY area...

 

Thanks I appreciate the info. Ill give it a try.

 

There is an inherent buzz/vibration/resonance around that rpm....

Sometimes it easiest to stay just above or just below it.

Also, though, the first thing I would check---would be the clamp that holds the right-side chrome heat shield/trim onto the collector box by your right foot. They are notorious for having the front ring break, the the shield itself will buzz like crazy around that rpm. Easiest way to tell.... When you're at the rpm and your buzzing away, just turn your toe in against it and see if it stops

 

Ok thanks I will

 

same exact thing on my 82' XJ650. they are just a bit buzzy at that range - and I HAVE tried to fix it. Now I just do what other people do and just avoid that RPM range although it is annoying to have to do that - especially since we are missing that 6th gear. Same RPM range (except mine is 4,800-4,900 RPM's then again at 5,200 - 5,400 RPM's. I've tried a lot of things - lead shot in the handlebars, vibranators, etc. what helped the most was dual density grips which are made to absorb vibration (Pro Grip 724's is what I bought) and then I put Grip Puppies (foam grip over them). Very nice feel, I like the wider diameter of the grips with the Grip Puppies on there. I think the only thing that could stop it since it's coming from the engine (harmonic distortion) would be a counter-balancer. I've been meaning to replace the rubber engine mounts since they are old and hard but I still doubt it would do much. inline fours have an "inherent second order vibration that can't be eliminated no matter how well the engine is tuned"......unless you have a counter balanced shafts

 

wait.....you never felt any vibration until you broke an exhaust bolt ? I have three of these bikes, and hogfiddles has probably had hundreds, they do vibrate ever so slightly in that RPM range. and when I say vibration, it's not something you can see, you may feel it a little in footpegs and after a while in that range my hands will be a little numb. my bike is synched and tuned and runs great, I don't think any amount of tuning will get rid of the harmonic distortion created by a running engine

 

I have/had/will have again a 82 Maxim 650 as well. I rebuilt almost everything on the bike excluding the bottom end of motor (look at link in sig). Had the exact same vibration around 5k and tried almost everything to track down. Felt it most in the seat and the gauges would rattle but otherwise nothing felt out of place. The only thing I did not do was replace the rubber motor mounts. Could be the issue but never got around to it before the bike was wrecked. I just lerarned to avoid the range as I rode.

 

Fellas....that vibration was there when the bikes left the factory.

 

I just pulled the bike out of the shop about 2m ago where it sat for about 13 years ago when my dad bought it and there sat for 13yrs. After I got it going I ran it over 6k a few times and no buzz at all. Then I didn't run it too hard until recently where I would rev it over 6k here and there. Then one day I was coming up the hill and bang I heard the exhaust nut and stud bounce off the front fender then of course I had an exhaust leak. When I got home (which was only a 1/2m away) I checked and the other existing nut was backed off. Once I fixed everything and took it for a test drive the buzz was there and still is.

 

It's possible I just never felt it before but Im sure I would have questioned the buzz.

 

I don't know, I could easily see not noticing it running around town on it - my brother and I switched bikes for a couple of hours while riding this summer and he couldn't feel it at all in the handle bars - exact words "I don't know what you're talking about" - then I told him to go gradually get up to 4800 RPM's and stay there and pay a attention to the foot pegs as you come into that range, then he conceded that he could feel it. I agree with K-moe, the buzz was there when they left the factory. I wouldn't be trying to solve it at all but on long rides the hand numbing is annoying to me.

I have an extra set of handlebars so I think I'm going to try Bar Buzz Kill and also heavy bar end weights. NOT to stop the vibration mind you (because that's coming from the engine) but to absorb/counter it

 

problem solved

 

As we say in programming, “Not a bug— it’s a feature!!”

 

I just met up with a guy today that has an 83 Seca 750... he's not on this list at all. When we were comparing notes on our bikes I think it was the third thing he mentioned as "going on" with his... described everything here perfectly.

The exhaust thing listed above makes me wonder... we've been talking about engine mounts and everything else, maybe it's the pipes coming off the front and then to the collector that only has one bolt holding the whole thing down there.

My bike has the vibe but I also replaced every gasket in my exhaust from front to back. I also never-seized every bolt and gasket. Maybe once everything is loose, the collector / pipes are free to vibrate... with a decent size moment arm to that one bolt and then you are stuck with it. That would agree with the "It wasn't there before disturbing the pipe(s) and gaskets," etc. There was enough corrosion at every bolt / joint to keep everything solid and once disturbed that was it.

I might even suspect that the harmonics was the reason for the stud parting in the first place.

 

could be right, i don't notice it with a 4/1 pipe

 

just curious if anyone has tried either rubber butyl or the Bar Buzz Kill product in the handle bar and whether it had any effect at all. I can say the somewhat expensive "vibranators" that I bought didn't do anything for me. Since we are just trying to absorb the high frequency vibrations generated at specific RPM's I could see some sort of rubber bar-fill coupled with some heavy bar end weights deadening the bars significantly. We are planning a long trip out West next summer so I'd like to do what I can regarding my hand numbness problem (and no....I'm getting a new Harley like my crew is trying to convince me to do)

http://www.gripnripracing.com/index.php?id_product=109&controller=product
http://www.hvmp.com/7-8-Universal-s/23.htm

 

correction
.....and no, I'm NOT getting a new Harley my crew is trying to convince me to do

 

That was going to be my next question. Do the folks with 4-1 get the same thing?

 

I filled my bars with butylene rubber caulk. It does dampen the vibration at the bars, but it's not eliminated (in part due to my having aluminum bars instead of the stock steel bars).
Between that and a pair of gel-padded gloves I can ride all day without aggravating my various injuries. My hands get tingly, but not numb. In my case my ulnar nerves are easily pinched at the shoulder, so I'm not entirely sure how much of the tingling is from the bar vibration and how much is from posture.

I do think that adding bar-end weights might just dampen the higher-frequency vibrations entirely, but haven't bothered to try that yet.

 

As a data point, I had the 5k buzz too, then I replaced my exhaust with a 4-1 after rust made it the best route for me. I didn't do it as a troubleshooting step for the buzz, but I did notice following the replacement that it was gone. I also did a full carb cleaning and tuning as part of that, so it's possible I got my synch better or my tuning more spot on. That being said, it seems to be /gone/ with the 4-1.

 

My mission in life is now to create a clamp / damper for the front pipes and see if it works....

 

The right amount of mass in the correct place might just do it.

 

I'm thinking start with a couple pieces of flat stock and some glass braided material like the gaskets on my hi temp kilns here at work. Just for a ride and proof of concept. Then if it works consider making something that looks nice...

View from above:

 

Nooo. Just think about this. If it vibrates from the exhaust pulses with engine running it will rattle if you hit it with a mallet. So get a rubber mallet and tap the pipes, one at a time, listening as you go.
Whatever gizmo you expect to fit, it will look dreadfull, don't do it