Swelling tanks - is it a problem for Grisos and other CARC bike’s

[nashopolis]

As I look at used Grisos - I started reading threads about swelling tanks which I hadn’t noticed before.  I knew it was a problem for the v-7s

How bad of an issue is it?  A few bikes I’ve inquired about  have peeling stripes.  I’m assuming this means the tank has swollen a bit.  Aesthetics aside is tank swelling causing owners grief?  Things like leaks or failures or making it impossible to get the tanks back on kind if issues?  Needing to buy a new tank would be a total bummer.

Noticed some folks were having the same issues on Stelvio’s too. 

[Bert Remington]

I bought my 2012 Norge in 2018 used.  When I removed the tank holddown bolt, I had to use a tie strap to pull the tank back into place.  There were several large blisters mostly in the front of the tank.  I wasn't brave enough to pop any of them.  Bought another NOS tank for $150.  A few months later, I didn't bother to warm the engine, it backfired and I tipped into a fence post.  I left the tank scar as a warmup reminder.

When you remove the tank holddown bolt, if you can't restart the threads without another person or mechanical aid then consider a tank replacement.

[Bobic69]

Never had an issue with my plastic tank V7.

[Motormike]

All plastic fuel tanks are affected by ethanol, some more than others.  The plastic used for most Moto Guzzi fuel tanks (V11, Norge, Griso, etc.) is PA6 Nylon.  If you open the fuel cap and the inside of the tank is a white plastic, it is PA6 roto-mold Nylon. Unfortunately, it is the most affected by ethanol fuels.  It will swell in size, and may, over time, out-gas where the fuel vapors leach through the tank and cause bubbles in tank decals, and other paint issues.  The plastic tanks are all made by Acerbis in Italy.  They have been used by Ducati, Moto Guzzi, Triumph and others.  The manufactuer likes the material because it is paintable. Many manufacturers, like Ducati and BMW, have switched material to a black waxy plastic that cannot be painted.  It's similar to the plastic used in common lawnmower-type gas jugs.  Because it can't be painted, the tank is usually covered in a painted ABS plastic shell.  Unfortunately, even these fuel tanks expand slightly when exposed to ethanol fuel (ask any BMS gs 1200 owner...like me!) but not nearly as bad as PA-6 nylon tanks.  As mentioned, those can expand enough to make removal and re-installation a real chore!  Look closely at the front of a Norge fuel tank.  Every one I've looked at, the upper triple clamp has made enough contact with the tank to at least chip the paint.  By the way, none of the ethanol fuel treatments on the market will stop the plastic fuel tank expansion issue.  Some have lined the inside of the tanks with Caswell epoxy, but there are stories of the coating separating inside the tank.  I always say take a small magnet when you shop for a motorcycle.  If the magnet won't stick to the fuel tank...well, you've been warned!

[Scott of the Sahara]

Have had my '08 since '010. No Problems so far. It is sometimes tough to get the tank back on, but I have managed. I hate the Ethanal.

[Motormike]

It's actually the water that Ethanol gas holds that causes all the problems.  Here's a link that explains the absorbent characteristics of PA6 Nylon.  You don't have to read the whole thing, the first sentence says it all:  https://www.toray.jp/plastics/en/amilan/technical/tec_003.html

[nashopolis]

Makes sense acrebis makes dirt bike tanks that stickers won’t adhere to -assuming it’s the same material...
Interesting confluence of conflicting manufacture and situational use priorities.
If it’s not a fatal flaw I reckon it’s part of modern fun

I too was thinking Caswell lining might be an option if you had a new bike but on used bikes the damage is probably already done.  Caswells seems way better than the redcoat flaking off in my triumph’s  tank - I’ve had friends use the epoxy with success. 

Has anyone ever reversed the process by drying out the tank?  Paint wouldn’t be helped but fitting it on a bike might. 

[Dilliw]

Has anyone ever reversed the process by drying out the tank?  Paint wouldn’t be helped but fitting it on a bike might. 

When I bought my used, out of warranty Griso it had 4-5  "pimples" on the top of the tank.  A few years of garage living plus an abundant use of ethanol free gas and all of the pimples have disappeared.   So I think there's hope that things can mostly return to normal if you remove the ethanol from the equation.

I do run ethanol fuels on the road and haven't had any additional issues.  In fact I have now determined that my bike likes 87 octane ethanol regular better than anything else.  I just have plan the last miles so I'm either out when I get home or when I get to one of several strategically located ethanol free supplies that I know of.  You don't want that stuff sitting in there.

[Pizza Guzzi]

2008 Breva V1200 ( not sold in the US AFAIK ) Zero issues with removing / refitting the tank. It never sees ethanol laced fuel though.

[kingoffleece]

Yep.  My 14 Norge has zero issues but I use E0 at home and where I can find it on the road.  For E10, I bring one shot bottles of Yamaha Fuel Rx which all the two stroke shops near me swear is the best of the best.  So far so good.

I'll also on the return trip home play "how close can I call it" so as to fill up with E0 upon return.

[guzziownr]

My '13 Griso tank is a bit swole and has some pimples but it hasn't gotten worse with time. It's not a great fit when you take it on and off but it fits. Tape stripes are starting to fall off. This isn't helped by the fact that the tank has grown since they were applied at the factory.

[JJ]

I have plastic gas tanks on both my Centuaro GT and my Victory Vision. 

Been using a "shot glass" full of this every tank fill...because the gas is soooooooo bad here in Arizona.

[Motormike]

Has anyone ever reversed the process by drying out the tank?  Paint wouldn’t be helped but fitting it on a bike might.

I've read reports that the tanks will shrink back (although usually not 100%) when left out in a dry enviroment.  The moisture absorbed by the nylon will eventually evaporate out of the materiel.  Or at least that's the theory.  The thing to remember is the plastic only absorbs a certain percentage of moisture, about 10-15% volume.  So the tank doesn't expand forever.  Once the maximum absorbtion is reached the expansion stops.  But as been mentioned here, this is still enough to damage the finish and make removal and installation of the fuel tank difficult to impossible.  Another problem is the fuel pump flange.  The flange can distort, resulting in fuel leaks.  Ducati had a recall on the first gen. Multistrada because of this issue.  Their "fix" was to change out the o-ring for a thicker quad-ring seal.