Author Topic: Strange resonance/vibration at 4000rpm (Read 6402 times)

GooseMan · « **on:** June 21, 2007, 11:55:53 AM »

Last saturday I went for a long ride with some friends. I noticed about halfway thru the ride that my bike seemed to develop this strange resonance at exactly 4000rpm, up till about 6000rpm.

Its as if something on the bike was vibrating at that exact rpm range...not more, not less, and in every gear. It's REALLY annoying.

The only thing I've done to the bike right before was wash it, but thats about it. I figured after I had the tank off and half the bike dissasembled for the valve job, I would have cured this resonance...but its still there!

Has this happened to anyone else? Any ideas for finding the source? It's driving me nuts!

Banditmax · « **Reply #1 on:** June 21, 2007, 12:20:42 PM »

Mines always had it i think. It did rattle at 4000rpm when my cam chain tensioner blade was worn back to the metal too.

pmackie · « **Reply #2 on:** June 21, 2007, 12:27:00 PM »

Check a couple of things, especially if you recently noticed a change:
1. Check all the engine mount bolts. You could have one come loose.
2. Check all you exhaust bolts, starting at the cylinder head and working back.
3. Have a good look at you chain and sprockets.

duane · « **Reply #3 on:** June 21, 2007, 04:40:23 PM »

When motorcycles vibrate it will happen at certain places in the rev range i.e 7000 to 10000 RPM's (as on my VFR). What you are describing sounds common. With the little Bandit's, others on this board have described the same thing, but it seems to happen at different places in the rev range, depending on the bike. Mine begins at 5.5k to 6k. I believe this is the nature of inline fours where the engine is a stressed member.

interfuse · « **Reply #4 on:** June 21, 2007, 11:36:16 PM »

I've always thought it was from improper jetting... depending on how my carb is setup the vibes switch rpms.

duane · « **Reply #5 on:** June 22, 2007, 12:52:32 AM »

Quote from: "interfuse"

I've always thought it was from improper jetting... depending on how my carb is setup the vibes switch rpms.

Well, that's a state of tune. The first thing do when chasing buzzes is to tune-up your engine. I'm a vetran of this game because I owned a Concours for many years and they buzzed alot. It became a black art dealing with that bike and it's buzzing.

After it's tuned properly, pmackie touched on this, go to the engine mounting bolts and etc. That's a whole nuther thread.

GooseMan · « **Reply #6 on:** June 22, 2007, 01:53:52 PM »

I dunno...I've had the bike for a month now, put 2000km on it, and never had any weird buzzing...and now, all of a sudden, its starting to buzz....I dont think its coming from the engine, its like, something seems loose and is rattling/buzzing with the engine. I'll check all the bolts and everything...hopefully I can find out what it is!

turbofb · « **Reply #7 on:** June 23, 2007, 12:56:51 AM »

Inline 4's have a natural secondary vibration that cant be helped.Thats why most larger 4 bangers (over 2.0L) will have a balance shaft or two.Smaller engines have less mass and the vibration can usually be tamed with mounting and chassis modifications during the design phase.
Both my bikes are 4 bangers and both have stressed member engines.....and they both have their little buzzes.The big FZR is much less noticable though since I still have all the rubber isolators on the pegs,forks and clip-ons.The Bandit's buzz is not very intrusive since its such a small engine,but its noticable due to the solid mount bars and pegs.

As stated,check your tank,engine/chassis bolts,suspension pickup points,head bearings,wheel bearings,kick/center stands,ect......anything that can move and vibrate,will have a resonance at some RPM/MPH.......

JamesBanditVV · « **Reply #8 on:** June 23, 2007, 04:12:33 AM »

mine does the same, it buzzes from the same revs as yours, but i was swaying towards cam chain chensioner as i got a stethascope and had a route around the engine for the noise ans seemed to locate it to that area

andrewsw · « **Reply #9 on:** June 26, 2007, 01:15:26 PM »

there's definitely a couple points in the rev range where the valve train and cam tensioner make some noise and I think that's normal.

But if you've got a sudden new noise, that's probably not normal. How about valve adjustment?

GooseMan · « **Reply #10 on:** June 26, 2007, 02:10:04 PM »

I just did the valve adjustment!

It's weird because it started happening a little while before the adjustment, so I figured it would go away after the adjustment, and after taking apart a lot of the bike and putting it back together (I figured maybe the tank was loose or something)....but its still there

How hard is it to adjust the cam chain tension?

Banditmax · « **Reply #11 on:** June 26, 2007, 02:32:29 PM »

Cam chain tensioner isnt adjustable. although you can check its working have a look at the manual.

andrewsw · « **Reply #12 on:** June 26, 2007, 07:52:36 PM »

Gooseman reminded me that he

Quote

... just did the valve adjustment! Wink

yup. we talked about that... heh.

cam chain tensioner: there is (or should be) a little black rubber plug on it. you can remove it (with a fingernail or pocket knife or whatever). Inside is a tiny slotted screw head. Clockwise locks (and maybe retracts?) the tensioner. Counter-clockwise frees it up again so the spring can push against the chain. The chain runs over a guide inside the engine between the cylinders. You can get wear in the guide or the spring in the tensioner can fail, either of which would cause some noise from that area. AIUI, if the spring is bolloxed up, you can pull it apart and trim off the busted end and it will still work, but I've not done it.

PitterB4 · « **Reply #13 on:** June 26, 2007, 09:38:52 PM »

Did you synch the carbs after the valve adjust (which I believe is SOP)? My little B4 was really picky about the synch of the carbs. Anytime she seemed a little rough, she'd purr like a kitten after the synch. 'Course... I was always f-in' around with stuff, too.

(Must leave the Kawi totally stock... MUST leave the Kawi totally stock....)

andrewsw · « **Reply #14 on:** June 27, 2007, 01:59:52 PM »

Pitter B4 thinks he can

Quote

... leave the Kawi totally stock... MUST leave the Kawi totally stock....)

heh. yeah right.

gotta second the carb-sync. And I love my $3 differential-manometer*. It gives spot on carb sync in nothing flat.

*clear tubing with colored water. works like a champ, unless you're way out, in which case it just sucks up all the water. I've heard oil is better, but I think its to slow and not as precise as the water is. .02