Bad vibes at 5500rpm

**tkent02** · 03-14-2008, 08:07 PM

Originally posted by Skyboy8950

Whether in neutral or any gear, at 5500rpm, I start to get some intense vibrations. There is no vibration before, but when I get to 5500+, there is definitely vibration.

This started after I replaced my headgasket. When I replaced the head gasket, I also re-shimmed the valves. I believe only 3 were off, and not by much. It vibrated before and after re-shimming. I also synched the carbs. It vibrated before and after synching. I adjusted the fuel mixture. It vibrated before and after adjusting the fuel mixture.

At this point, I don't know what is going on. For some reason, I want to think that it has to do with chain tension and at 5500rpm, the chain likes to slap around a little bit. I have no reasoning why I think that, and that is probably not the reason.

If you have ANY suggestions, please let me hear them. I would love to get rid of the bad vibes!

Is this at any RPM above 5500 or just certain RPM bands?
If it started with the head being removed, what did you disturb?
Perhaps the cam chain is off by one tooth on one cam or the other?
Cam chain adjuster get too tight or too loose somehow?
You sound like you know you did the valve clearances correctly, what about the synch?
Might try resynching it at a different RPM.
Is it still running correctly other than the vibrations?

**Skyboy8950** · 03-14-2008, 09:08 PM

Thanks for your reply,

It is vibrating at everything above 5500.
I don't think I disturbed anything. I removed the chain tensioner and installed it again. As I see it, there is no adjustment on the tensioner. Simply push the spring in, lock the screw and nut, install tensioner, loosen nut and screw slightly, hear the noise, then lock the screw down again. Is this right?
The bike runs super great otherwise. If the cam chain was off by one link, I would think the bike would run very poorly. I double checked the specs and what I did when I reinstalled the cams. The sync, I used the Carbtune at 2000rpm and was very satisfied with the way that turned out. When adjusting the fuel screw, I found a range that made the bike run its best and set all carbs to that.
Tomorrow, when I fire it up, I will re-sync the carbs. Thanks for all your questions. I hope my answers have shed some light on the problem.

**1980GS1000E** · 03-14-2008, 09:17 PM

I don't know if you tried this, but loose motor mounts can definitely cause vibration.

**tkent02** · 03-14-2008, 09:25 PM

Originally posted by Skyboy8950

The bike runs super great otherwise. If the cam chain was off by one link, I would think the bike would run very poorly.

Not necessarily. If you are off one in the direction of the two cams being timed farther apart, it could pull more like a tractor, if the cams are closer together, you get a narrower powerband, perhaps more peak power at the expense of midrange. There is a lot of variation in how the cams are timed from the factory, not much quality control there from Suzuki. One tooth off is about ten degrees, a huge change, but it wouldn't hurt to check if you can't find any other problems. The GS750 I bought a while ago was off by one tooth from a previous "mechanic", it ran as well as could be expected given the other problems it had at the time. I can't remember which cam it was or which direction it was off.

**duaneage** · 03-15-2008, 12:01 AM

Check compression. If the valves are off your compression might be lower. ultimately I think your going to have to check the valve timing by opening the top and peering inside.

**Skyboy8950** · 03-15-2008, 12:43 AM

Well, there is a lot to consider here. Thankfully, pulling the cam cover isn't that hard, so I can probably get around to that. I have the specs on how to set the chain in my manual, but to verify, does anyone have the specs for my gs650gl? Also, I can definitely check the motor mounts. I didn't think of that. Thanks again for all the suggestions.

PS. I have noticed what I believe to be lower performance, so this leads me to think you are correct. But would that still explain my vibes?

**duaneage** · 03-15-2008, 08:09 AM

GL motor is the same as the G motor, no difference.

Vibration can be caused by on cam being out of sync with the other, changes cylinder pressures, or could just be something else. If you pull the cover you'll know.

**waterman** · 03-15-2008, 10:33 PM

I have noticed a vibration in my 650 around this rpm range also. I am not sure if it isn't just a resonance frequency of the motor; ie where all vibrations actually build up to vibrate as one. I had noticed some different buzzing and found that a set of highway crash bars were contacting the exhaust pipes which led to extra noise. I would check to see that the exhaust heat shields and other accessories are tight and not adding to the noise. On my 550, I have a loose front fender that rattles around at certain times.

The valve timing on these 650 is a little strange in that when you set up the exhaust cam the arrow needs to line up with the gasket area of the valve cover. The strangeness is that it doesn't line up well with the gasket, but will appear slightly under parallel. I have encountered where a previous owner had it set a tooth too high, with the arrow pointing parallel to gasket surface. I didn't check to see if there were 20 links between intake and exhaust cams, but bet it was off a tooth also. The bike ran okay, but didn't quite sound right. Please note, I am pulling this out of my head about the 20 links, I remember the chain drive 650 were one link less between cams. Please verify in manual, before using. Good luck sleuthing out problem and report back any solutions.

**Steve** · 03-16-2008, 12:09 AM

Originally posted by Skyboy8950

Simply push the spring in, lock the screw and nut, install tensioner, loosen nut and screw slightly, hear the noise, then lock the screw down again. Is this right?

Almost. :shock:

Push the spring in, lock the screw and nut, install tensioner, loosen nut and screw slightly, hear the noise, then turn the screw until it touches, and back out about 1/2 turn, then lock it down. Do not leave it tight or it will not be able to take up slack in the chain as necessary.

.

**Skyboy8950** · 03-16-2008, 10:14 AM

Waterman, so what you are saying is that both cams could be off by one link? Interesting. I didn't open it up yesterday because of rain (geez i want a garage) but today the sun is out in full force. When it comes to performance, in second gear, I can open the throttle up all the way and wait a few seconds until I have to shift. Not very zippy. I don't remember that before I replaced the head gasket. Also, the vibrations were not there before the replacement. I will hopefully report back with great news later. Thanks again everyone.

**Skyboy8950** · 03-16-2008, 11:59 AM

UPDATE!

So I pulled the cover, looked at the chain and its position. At TDC, the arrow points right where the gasket should be. If I move it one pin off, the arrow is too low or too high and therefore the exhaust cam is correct. I then counted many times the number of pins from one arrow to the next between cams: 20 as it says in the manual. The timing is correct and everything looks good. The next thing I am going to do is pull the tensioner and try that again. I'm pretty sure I did it correctly, but it never hurts to do it again.

Thanks again for the help. I'll keep you posted.

**Skyboy8950** · 03-16-2008, 01:38 PM

UPDATE AGAIN!

Ok, tensioner was installed correctly. I buttoned everything back up and when I did, I checked the motor mounts. One of them had one bolt completely loose, the other bolt was loose a bit, so I snugged it up. Tried to start the bike, no luck. Have to go get some gas. Then I will try again.

**Skyboy8950** · 03-16-2008, 02:36 PM

Prognosis: Negative

Got it started and took it out for its first ride of the year. Same as last year, vibes about 5000 or so on up. Motor mounts are tight, carbs synced, timing great, arg. Well, I'm going to be selling this thing in the next month, so I guess it will be someone else's problem. But I am still taking suggestions if you have any.

Thanks for the help.

**p_s** · 03-16-2008, 02:40 PM

Wheels balanced? Carb sync tool calibrated?

Bad vibes at 5500rpm

Bad vibes at 5500rpm

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