Gas tank oscillating at high speed

[lukeman]

Has anyone else have the gas tank front wings vibrate at higher speeds?  80-100mph. 

The front wings of the tank begin to shake in and out during high speed which in turns causes the entire bike to shake.   I have everything secured properly, but the front plastic brace doesn't really make contact with the tank and seems flimsy anyway.  Maybe i'm missing something.

Just curious if anyone else had run into this? I was thinking of adding some rubber to the front brace to put some pressure on the plastic tank tips.

[Bixxer Bob]

The two frame spigots should have rubber buffers on the ends which locate snugly into the tank recesses, if that makes sense.  Sounds like yours may be missing?

[lukeman]

Yeah, those are there, the problem is that the left side of the tank is about a half inch away from there.  The PO had dropped the bike at some point, wonder if the tank is warped.

[Bixxer Bob]

Not talking about those, talking about these:

[matts23]

Mine has that gap that you are showing and doesn't move at all.   That isn't the problem.

[lukeman]

I'll pull off the tank this morning and have a look at it.  Something is wonky thats for sure.  Thanks!

[TigerTrax]

My money says the PO cinched down the rear bolt tight and the tank wasn't resting properly.... then
bolted down the top bolt.... and he had a tough time doing so.

[lukeman]

Took the tank off this week to have a look at things. 

Are the metal pieces attached to the turn signal section which gets screwed in near the forks under the instrument panel?  I could take off the pieces without removing the screws because they were not attached.  I couldn't even remove the screw because the metal pieces were turning in the slot where they were positioned. It seems to me that they should be pretty snug in there to so that the screw can be backed out or screwed in.  Having them attached would add more substance to the plastic tank it seems. 

[Bixxer Bob]

Maybe it's late, or maybe I'm being thick, but I didn't get your meaning. Any of it.

[lukeman]

Yeah I figured it might be a bit of a bad description.  So i've pointed it out below. 

Is the metal stud secured in the plastic piece holding the signals, or free to stay attached to the tank like this picture.  I can remove the tank without removing the screws which holds the metal stud in place.  Which basically means its not securing anything.

[Timbox2]

Somethings not right, all that should be left on the tank is the grommet. A screw goes in from the inside that holds the indicator pod in place, so yeah, think that metal bit should be still attached to the pod, or Mr Bodgett has been at work in another life.

[vince]

Somethings not right, all that should be left on the tank is the grommet. A screw goes in from the inside that holds the indicator pod in place, so yeah, think that metal bit should be still attached to the pod, or Mr Bodgett has been at work in another life.

+1 on what he said
Mine has that gap that you are showing and doesn't move at all

[metalguru]

Both my spigots have come unattached from the indicator pods mainly due to the tank changing shape. The tank has changed shape by 10mm on one side making the gap first shown between the fairing and tank. The lugs supporting the indicator pods have also deformed.
A good tip when taking the tank off is not to leave it off for too long.

I would be inclined to check the front wheel balance/bearings/run out as the oscillation must be sourced from vibration as the speed is not high enough for air currents and harmonics should not exist. The steering head bearings could contribute too.
Are the tyres in good condition?
Cupping, bulges, uneven wear could contribute, elevate both wheels to check by spinning and looking for anything out of round.

[Sin_Tiger]

  the airflow alone is not likely to create that effect.

[lukeman]

Ok here's an update.

I was able to improve the high speed stability to the point where the bars are still at high speed with hands removed or loose.  This has removed the extremely unnerving sensation.  Its made a huge difference.

As far as airflow being the cause, I agree that airflow alone wouldn't wobble the bike, but when it oscillated the gas tank plus the gallons inside it, it did.  I would have gotten some video of it (don't have a helmet cam), using one hand to give throttle at 85mph, while the left hand is filming and the bike is shaking didn't sound like a great time.  At high speed I can only compare what the tank was doing to sitting in a chair and moving your adductor and abductor muscles (thighs in and out) at a high rate. 
 
I took off the tank to check all the rubber bushings which the tank rides on, everything looked ok. From there I was able to epoxy the metal studs back into their seats in the turn signal plastic holder.   This allowed me to put the signals back on with the screws applying some stability to front two sections of the tank.  I'm not sure if everyone's tank is like this but the two front sections of mine are really quite elastic, able to be move inside and outside without too much resistance. 

I also added a felt pad (furniture) on each rubber piece at the very front of the tank to add a bit more pressure to the two wings of the tank. Overall the tank is rock solid now a hell of a lot more enjoyable to ride.

On another note. I think this bike has an alignment issue, driving a true straight line require the handle bars and triple tree to be point slightly left.  While doing this the wheel is pointed straight ahead.  I know the bike was dropped at slow speed on its right side by the PO, so I think something must have twisted. 

I'm not sure the best way to straighten it out.  Any ideas?  Was thinking I could loosen up the front end and twist it the other way.

Thanks for all the help!