how long for dry tank to shrink back?

[BK_856er]

Finally seeing some measurable shrinkage!  Lost nearly 1/8" between the bumper mounting holes.

Did the Marine Clean treatment today.  Diluted 1:2 (cleaner/water) and sloshed 1.5gal in the tank for 15min.  Temps were ~75F and tank was warming in the sun most of the day.  Then I rinsed with 5 tanks of water which took another 30min.  The drain valve was awesome.  Wiped dry and put under the fan.  After it fully dries I'll add back the desiccant and seal it up for more storage.

The cleaner definitely took off some yellow on the fill neck area.  Cool.  I had previously washed with dish detergent.

What's the recommended contact time for the Marine Clean?  The instructions suggest overnight for varnished fuel tanks, but that's presumably for metal tanks and not nylon.  I didn't want to overdo it.  Curious what others have done.

BK

[ducatiz]

The next experiment involved adding a couple pounds of freshly activated desiccant, using the beautiful plug to seal the pump opening, in order to achieve very low internal RH.  Let's see what that does for a while.  My POR15 Marine Clean arrived today, so I'll queue that up next.  On particularly warm sunny days (this is northern California) I put the tank outside in direct sun where it gets hot to the touch for hours.  My goal is to get this b*tch shrunk down by ~May.

BK

Marine clean needs to be reduced with water to about 5:1 or more. 

Hair dryer is really your quick drying method.   Desicant will likely work but slow And it might be a test of the plastic vs desicant.  Best bet is something to move air Into and out of the tank.

You may find the PA6 is a stronger desiccant than the silica.

[ducatiz]

Finally seeing some measurable shrinkage!  Lost nearly 1/8" between the bumper mounting holes.

Did the Marine Clean treatment today.  Diluted 1:2 (cleaner/water) and sloshed 1.5gal in the tank for 15min.  Temps were ~75F and tank was warming in the sun most of the day.  Then I rinsed with 5 tanks of water which took another 30min.  The drain valve was awesome.  Wiped dry and put under the fan.  After it fully dries I'll add back the desiccant and seal it up for more storage.

The cleaner definitely took off some yellow on the fill neck area.  Cool.  I had previously washed with dish detergent.

What's the recommended contact time for the Marine Clean?  The instructions suggest overnight for varnished fuel tanks, but that's presumably for metal tanks and not nylon.  I didn't want to overdo it.  Curious what others have done.

BK

I would not leave the marine clean in for more than a few minutes at a time.  The tank will just absorb it too.  The point Is to flush the petrochemicals out.

2:1 is way too much.  5:1 Should be the max.  You're dealing with a tiny remnant of gas, not clumps of grease so you should go very light.

You don't want the tank absorbing the marine clean.

[BK_856er]

I'm experimenting with a few different techniques.  As an experienced research chemist I'll navigate this a little differently.

Not too worried about the Marine Clean absorbing into the tank in the short term.  The product comes as 90% water plus <5% KOH and <7% EGMBE + some nonionic surfactant.  Diluting it 1:2 or 1:10 for brief contact won't matter.  My interest was in removing any potential surface deposit (gum/varnish/aliphatic/hydrophobic/etc.) that could inhibit desorption of the water from the solid phase.

Nylon will not compete with a real desiccant.  I'm not using silica, but something similar.  The purpose is to decrease the internal relative humidity to a very low level to help drive the equilibrium.  I already tried continuous forced airflow for several weeks.

Passive shrinkage takes a lot of time.  Just playing with various techniques to try and accelerate that shrinkage.  It'll never be "fast" due to the mass of the material and the physical processes, but maybe I can make more happen in the window of time I have.  I wish I had forced air heating in my house - placing the fuel pump opening over a floor vent for the winter would be just the ticket!

BK

[ducatiz]

I wish I had had you around when I was figuring out all of this 2 years ago.

I was very reluctant to use anything stronger than 10:1 Marine Clean because I was concerned it would get carried into the PA6 by the water.

I didn't try desiccants because I had a feeling the pa6 would "compete" but I couldn't be sure.  I knew that something needs to "push/pull" the moisture out of the material and heat/low humidity is a sure fire way of doing it.

The main things I found were that you have to get rid of any old gas, which you're clearly doing, but you also should try to scuff the interior surface.  I actually used a dremel on a right angle with a 1/16" bit and a mandrel to make small divots in the material and key points.  You only need about a 2mm divot and with the very-liquid reduced caswells it will fill the divot immediately.  The divot gives the caswell's something to "hang" from and strengthens adhesion.

There is a good paper from the U. of Minnesota on PA6 and other materials absorption of water/ethanol/etc which is a little mind blowing.  THey don't talk much about removing it but the figures they saw were a little disturbing in light of this material being used in a fuel tank.

[BK_856er]

Thanks, I'll look into those papers to help educate myself.

I offered to help in the early days, but there was a lot of drama at the time.   

Some interesting pieces of information below, assuming water absorption is the main event.  "Reconditioning" at low relative humidity (single digit) should facilitate shrinkage if equilibrium can be achieved.  Elevating the temperature will help.  Kinetics will be slow regardless.  The painted exterior surface should render that surface inert and therefore the room relative humidity irrelevant if the tank openings are sealed.  Most of the literature is concerned with rates of absorption, not desorption, and the focus is usually on water and not fuel components.  At room temperature the rates are very slow, so brief water treatments are safe.  I don't think I'm showing anything new here, just capturing some concepts.

BK

The relationship between relative humidity and PA6 absorbed water:



The relationship between absorbed water and dimension:



The kinetics of water absorption under various conditions (governed by Flicks law):



An automotive trade group comparison of various materials vs. conditions:

[BK_856er]

6 month update.  I've had my tank in storage, sealed up with some desiccant inside.  The dimension between the bumper mounting points stabilized at a bit over 11.5" long ago, just like OrangeDragon reported.  I don't believe I learned any tricks for speeding up shrinkage.  Time for Caswells and some riding.

BK

[ducatiz]

6 month update.  I've had my tank in storage, sealed up with some desiccant inside.  The dimension between the bumper mounting points stabilized at a bit over 11.5" long ago, just like OrangeDragon reported.  I don't believe I learned any tricks for speeding up shrinkage.  Time for Caswells and some riding.

BK

best trick is to move air, as you implied above.  i have a small hair dryer that fits right into the filler.  dries the tank out pretty well on no heat.

[czen]

I had two warranty tanks due to expansion.  Current one has now swelled to the point where lifting the tank takes tools, but it's off, fuel pump is out and it's bone dry after putting a fan through it all night.  I've heard that the tanks will eventually shrink back to their regular size if dry.  How long does this take and are there known methods to accelerate the process?  Given the mass of the material and the fact that it takes a couple years to swell up, this has go to take a while, right?

BK

This is an interesting and useful thread. After I purchased my 2006 S2R1K about 3 months ago, I noticed the usual symptoms of gas tank swelling. The previous owner was very likely using ethanol added gas and had left the tank full over the winter.

At first I was quite concerned the problem would get worse and that I'd have to go through the drying process, etc. However, after going through a few tanks of good, non-ethanol gas, oddly enough, the tank shrank down noticeably. For example, before, the clutch side button panel was touching the tank when handlebars were turned all the way left; now there's a few mm clearance.

This, I realize, is probably unusual ... but I suppose it could happen to others.

I also used Seafoam a few time in the gas to clean out the system, but I doubt this had any relevance to the tank swelling/shrinking issue.

[ute]

so the measuring point is center to center of the holes ?

If so the tank I just got is 11.25" outside to outside hole is almost 11.5"

Would you advise caswelling now or wait till start of next season .   And for drying how about in the garage over winter average temp -10c  ...freeze the moisture out ...lol

[BK_856er]

Sounds like you're all shrunk up at least in that dimension (yes, center of the holes is the place to measure).

How about clearance to the ignition cylinder?

Clean/dry/shrunk I'd say coat at your convenience and when environmental conditions are optimal.

BK

[ute]

Dry fit switch looks good ...ok will line next spring. I will keep it in basement with furnace heat blowing through it.
Thanks

[ute]

So does the Caswell smell ? can i do it in the house , in the basement ?

Or will Mrs ute take a fit because of the smell ............lol

[ducpainter]

So does the Caswell smell ? can i do it in the house , in the basement ?

Or will Mrs ute take a fit because of the smell ............lol

Yup...

and you know how she reacts to stink better than I do.

[ute]

Lol ..not good