I have read a lot about the GS500 having the fuel tank resonate. My bike is an 08 GS500F with a little over 6,200 miles on it. Over the weekend, I replaced my fuel tank, due to a dent in the original one. After I went to the gas station and filled up for the first time, I began to notice this annoying resonance that develops almost exactly at 2500 RPM. It gives off a sort of rough vibration through the whole bike when you are both accelerating and decelerating past the 2500 RPM mark.
In my case I don't feel like the resonance is coming from the gas tank...although I noticed after I replaced the tank; and it never did it before with the other one. It really almost feels and sounds like it coming from the engine, but the bike is smooth at all other engine speeds. If anyone has any ideas please let me know. This resonance is driving me crazy. Thanks.

Off-topic, but if you have a dented tank, I would be interested in buying the old one, assuming it's rust free. Would be good to have a spare for the race bike, and I don't need a pristine tank. What year?

Regarding your original question... I haven't heard anything about vibrations or resonance in the fuel tank. The first question I ask when tracking down this kind of problem is whether the issue seems to be related to wheel speed, or engine speed. Does it go away when you pull the clutch in? Does it change frequency when you shift? All of these will help tracking down the problem.

When you changed tanks, did you install the rubber trim, and the rubber cushion for the forward tank mount? If either of those are missing, you might either get some play, or some metal on metal vibes.

my bike was like that when i first got it because it was missing the rubber trim on the bottom edges of the tank. i didn't take note of the rpm.

noise did not completely disappear with the new rubber trim but its really hard to notice without paying mind to it.

A few things.
Rubber bumper at front - is it on the frame? It slips over the frame and the tank slips into it. If there, maybe you put tank on top of it and not slide the tank forward onto it?
There are 2 rubber bumpers under the tank. They usually get lost. Are they there? If not, take them from old tank or make bumpers stacking up some pieces of neoprene foam, window neoprene sticky back stuff or something else.
Seat catch: is that properly installed with the rubber bumpers?
Bolts: is it bolted tight to the frame?
Trim: well, iffy there. It is more decorative than anything else. It might touch at the front. New tanks only have it at the front, older tanks have it going all the way around. Be safe. Like burning1 said, put it on if not there.

The 2500 rpm is probably the resonant frequency of the tank with gas in it. That RPM should go up and down as the tank gets more or less gas. Like a glass with water - ringing frequency varies with amount of water in it.

I am going to try to answer a few of the questions. First it has no relation to wheel speed. I can play with the throttle stopped in neutral and find the spot where I start to get the noise.
Now, I just went and verified the installation of the tank. The tank is slipped into the rubber cushion in the front that is attached to the frame. I did transfer the 2 rubber cushions on the bottom of the tank from my old tank. There is a small piece of rubber trim on the front edge that seems to only be decorative. The seat catch has rubber cushions on it where it bolts to the bottom of the tank. As far as I can see there is no metal on metal. Everything also seems to be well tightened down.
I did try to rev it with the tank lifted off the frame, and I think I was still getting the sound. This leads my to believe it could be unrelated to the tank. The sound doesn't really sound like metal on metal.
Just as a point of reference, I have recently replaced my stator cover, changed the oil w/ new filter, installed T-rex no-drill frame sliders, and cleaned the air filter. I don't think any of these things could be contributing but I just thought I would put this out there.
By the way I have some new pictures of the bike that I need to post now that it is all done, and everything is replaced. And in regard to the tank I will PM you.

Quote from: adidasguy on October 10, 2011, 12:25:16 PM
A few things.
Rubber bumper at front - is it on the frame? It slips over the frame and the tank slips into it. If there, maybe you put tank on top of it and not slide the tank forward onto it?
There are 2 rubber bumpers under the tank. They usually get lost. Are they there? If not, take them from old tank or make bumpers stacking up some pieces of neoprene foam, window neoprene sticky back stuff or something else.
Seat catch: is that properly installed with the rubber bumpers?
Bolts: is it bolted tight to the frame?
Trim: well, iffy there. It is more decorative than anything else. It might touch at the front. New tanks only have it at the front, older tanks have it going all the way around. Be safe. Like burning1 said, put it on if not there.

The 2500 rpm is probably the resonant frequency of the tank with gas in it. That RPM should go up and down as the tank gets more or less gas. Like a glass with water - ringing frequency varies with amount of water in it.

I took the rubber trim off the front of my gas tank because it kept falling off. It's a really shoddy seal. I don't have any resonance issues at all. My major thing is only when I decelerate hard my front cowl shakes. Probably a loose screw somewhere.

Let me know what you guys think of this. So I installed the T-rex frame slider kit. It replaces the front engine mount bolt. The ends of the new bolt touch up against the inside of the side fairings. Could this be causing the sound? I can see that it has definitely been hitting on the plastic.

Quote from: mlutz9004 on October 10, 2011, 06:04:44 PM
Let me know what you guys think of this. So I installed the T-rex frame slider kit. It replaces the front engine mount bolt. The ends of the new bolt touch up against the inside of the side fairings. Could this be causing the sound? I can see that it has definitely been hitting on the plastic.

Very possible. Take off your plastics and see if it vibrates still. If it doesn't, you have your answer.

You could slip a piece of rubber, felt, leather, or something else to dampen the contact there and see if it goes away - or changes.

Just pushing on various parts of the tank with your fingers will dampen the vibration. Touch stuff till you can make it go away on command. Should really help localize the problem.

And yeah, Resonance; going to go with something being a little loose. Or something touching that shouldn't. Or missing spacer/zip tie.

if the bolt is to long you dont want it touching plastic as the plastic flexes when on the move.(trim bolt)

I had the same problem a while ago, turned out to be the rudder bumper thing under the front of the tank was missing. I found a lump of rubber that i cut to roughly to size, and duct-taped it into place. Problem solved!

Problem solved. It actually had nothing to do with the gas tank as I suspected. It was all in the frame sliders. There are spacer sleeves that go over 2 of the bolts on the crankcase cover. One was slightly loose which was causing a vibration resonance.

Nice catch. Glad it worked out.

Sent you a PM on the tank BTW. Let me know whether or not that going to work for you.

Isn't 2500 RPM a bit low to be accelerating anyway?