[Spitting Bull]

I find that when the fuel in my tank starts to get low, the tank seems to amplify engine-noises.  I get a very tinny noise which sounds like clattering valves, but the sound diminishes quite a lot if I grip the tank with my knees.  By gripping and releasing I can almost switch the sound on and off!  The tank isn't loose, and there's no problem noise when the tank is full, just that lovely thump-thump-thump.  I think the near-empty tank is just acting like a big, tin drum.

If I got some of that sound-deadening material that they use in the engine-compartments of cars - looks like half-inch thick felt - and if I glued a layer of this to the underside of the tank, would it make any difference?  What do you think?.

Tom

[c1skout]

I would think that might do it. You don't want to get that stuff soaked in oil and caught on fire though, don't ask me how I know.

[oldsalt]

Check out www.earsc.com.  The outfit is E-A-R Specialty Composites.  I've used some of their products in the design of material handling equipment.  Read vibratory conveyors.  Besides being self-distruction devices they are capable of making a lot of noise when a "hard" product is being conveyed.  A layer of "acoustical foam" adheared to the outside of the conveying surface really works to dampen the steel surface.  [Properly, it damps; Dampen is what you are doing when you put water on something].   Will it have a salutary effect on the RE tank if's is applied to the bottom surfaces?  I have no idea what will happen.  However, E-A-R makes foam that can withstand considerable radiant heat.       

[dogbone]

There is an antislosh foam used in fuel cells that may work. My 99 Bullet has the same vibration, I have covered the frame under the tank with a piece of old innertube, it helped. I usually ignore it, but a good leg squeeze on the tank will quiet it down

[Thumper]

I took a strip of white packaging foam (the kind that seems to be halfway between styrofoam and cushion foam, sort of translucent) and glued it to the frame backbone for the tank to sit on.

This was to support the tank while waiting for a replacement tank after the weld on one of the rear tank brackets broke. The tank only had one rear bracket left and it started to make a lot of noise.

Matt

[geoffbaker]

If this is noise being transferred from the engine to the frame and the frame to the tank, you might consider adding some rubber washers and or rubber type cement to the two bolts that hold the tank on. By reducing even slightly the vibration being transferred you may reduce the noise considerably.

You might try thinner, longer bolts in a rubber sleeve as well. You could make the sleeves yourself just using thin rubber.

I would think this might be more effective than spraying or adding anything beneath the tank - which would simply stop sound waves radiating from the engine below through the air to the tank, and not affect noise/vibration being transferred from metal to metal contact.

[Chasfield]

Tom

Is there any unwanted contact between your tank and the tower nuts that hold the rocker boxes in place?

My tank was being eaten into until I made some adjustments.

Have a look at my "Fuel Tank Clearance" post in Bullet Classic Models.

Chas

[Hack]

In the world of high end mobile electronics they have a variety of self adhesive sound deadeners, many of which are designed for high heat applications.  "Dynamat Xtreme" is one example. 
http://www.sounddeadener.com/Dynamat/Xtreme/index.htm
Applying it to the underside/nonviewable portion of the tank should help eliminate resonance.

[Kevin Mahoney]

One thing to look at is the engine steady strap ( the piece that goes from the rear of the head to the stud that mounts the rear of the tank. If they get loose it can sound like your engine is about to come apart,.

[Foggy_Auggie]

Make sure the bolts are tight at the front and back of the tank.  But don't strip the threads...

[Spitting Bull]

Thanks all, for yourconsidered advice.

Tom

[LotusSevenMan]

Tom

Has your tank got the screw - on or sticky pad knee pads? I have the rubber screw on ones and don't get this problem you mention here. Maybe these damp the sound???

LSM

[Spitting Bull]

LSM - sorry for the delay in replying to your post.  Ive been working in France/Belgium for the last 10 days so only just saw it.

My tank is the standard UK Classic one, painted finish and no knee-pads.

Tom

[jest2dogs]

A few years ago I saw a sound deadening material used on automobile body panels. It was about 1/8" thick and was like a heavy, "leaden" vinyl. I don't recall if it was self adhesive or if it would be resistant to engine heat, but it came in panels the size of a placemat and it was black. I found it in a local auto supply shop.

But I think Kevin is onto something with the head steady. I'd look there first.

-Jesse

[PhilJ]

I have been meaning to do this for a while now. Whelp, I did it today.
Mine is an 500 Classic AVL. I went to Lowes and got the Acoustic Tile. I waited tile the gas ran low so I didn't have so much to drain. Then measured and cut the tile and "contact cemented" the panels in place after painting the exposed portions flat black.

It took me longer than it would have 30 years ago but who's counting ! So after completion I put a pint in me and the bike so we could now fill up and check tank capacity (3.8 gal) the noise comparison. This puppy is now quite. The valves aren't near as noisy as I first thought. And after fill up it sounded like an overhead cam jobby doo.

Over all I'm very pleased, but of course if I had it do over (and I will) there is an area I could have done better on had I not been in such a hurry for my pint and the gin an tonic.