Aw crap!

[EVOL Tweety Bird]

Was able to locate a correct fuel tank for my mini, Tweety Bird. Read up on all the threads here and elsewhere on painting plastic fuel tanks. Invested in Caswell Fuel Tank sealer, followed directions to a tee. Even giving extra drying time before doing any painting. Outside sanded, applied adhesion promoter, and several coats of automotive primer. Let dry for a week. Wet sanded, then a 4 stage coat of paint/clear automotive lacquer, had the lettering airbrushed on, then cleared again.

Looked great, installed and added some fuel. Within a couple of days noticed what looked at first like maybe dirt in the paint, but I didn't remember them before. Another day or so the dirt looked like pimples forming, swelling up to a bean size. Poked a couple of them with a needle and the paint was soft and pushed down easily, but left a crater around them, like the paint around it was hard.

Looked inside the tank and it appears the sealer is lifting off from the plastic.

Well I guess I may have to install the old metal tank back on it.:angry:

 

[Havasu Dave]

Two things happened. (I guess you don't read my posts, but I don't blame you, I wouldn't either) Caswells does NOT work on plastic. I don't know the type of plastic, whether it's PTFE, or whatever, but even sanded, that epoxy does not stay adhered.

Assuming you didn't have fuel intrusion from the painted side, you had it from the inside, which has been discussed, but makes no sense to me that plastic would allow this breathing. Plenty of evidence that it does.

The only thing I have not tried is to flame treat the tank. There was a guy here talking about it, and I believe Markus did it, but did not elaborate. I guess the open flame hardens the plastic to the point where it accepts paint/epoxy better.

I'm sorry to see a four stage job get messed up. There just doesn't seem to be any bullet proof methods for painting plastic tanks.

Side bar; I had a leaking Cat plastic tank. That's when I tried Caswells and everything in between. NOTHING worked, until I cut up another black plastic tank and melted that plastic in to the Cat tank. That's it.

 

[EVOL Tweety Bird]

Dave did read your posts. Still figured I'd give it a try. Guess Caswell needs to change their ads,as they say right there it works on plastic fuel tanks... Oh well lesson learned.

 

[manchester1]

That's a shame. Everything I read about painting those tanks says nothing works.:shrug:

 

[older then dirt]

I feel your pain Brother. NOTHING worse then completing a stellar paint job and having it go to crap on you.

Last summer I had just finished spraying a boat in my garage. It was a nice deep blood red heavy metal flake. Turned out pretty good. It was still quite wet when my nosy next door neighbor cam over and said "Hey, looks great, is this dry... and touched it with 3 of his finger tips right on the front of the bow.
I could have shot the guy..:angry:

 

[EVOL Tweety Bird]

Yeah it sucks, I emailed Caswell the photos to ask for an explanation, doubt they'll do anything.
So. Maybe I should look for a metal tank cover and keep the stock tank under it. Or just go with a metal tank off something else.
Maybe a larger peanut style like it had before. Or I guess I can make a trip to the cycle salvage yard and see what they might have laying around. If anyone has suggestions I'm open to them.

 

[Havasu Dave]

Yeah it sucks, I emailed Caswell the photos to ask for an explanation, doubt they'll do anything.
So. Maybe I should look for a metal tank cover and keep the stock tank under it. Or just go with a metal tank off something else.
Maybe a larger peanut style like it had before. Or I guess I can make a trip to the cycle salvage yard and see what they might have laying around. If anyone has suggestions I'm open to them.

I may have found the reason it doesn't work, and why they say it does work on plastic.

Crosslinked Polyethylene used to used for plastic gas tanks among other things. However it's use is declining. Caswell ad specifically states their product wont work on polyethylene.

The chemical abbreviations for them are XPE, XLPE, PE-Xb, and PEX and according to the data I looked at, "applying filler or painting is difficult or impossible."

I looked in your build thread and couldn't find which tank you used for further research into it's chemical make up. I suspect that while XPE et.al use is in decline in the US, foreign sources are still using it.

Good post here by Gatecrasher on the subject.

I cant locate the posts by the guy who had a lot of plastics experience who talked about using an open flame to change the molecular structure of the tank to accept paint. I dismissed it, but I was probably wrong in retrospect.

I imagine after restoring the bike in the first place, you don't need advice from the peanut gallery, but either strip the paint off with a commercial product made for that purpose, or brake fluid and go with the plastic color and maybe some custom decals, or as you said, a metal tank, old or new, which might require some tabbing mods and a frame paint, but would allow another stab at tank art.

 

[markus]

my understanding of the flame treating is to help pull out the wax release agents from when they are molded and other contaminants that get sucked in from over the years. I do it on every plastic thing I paint....I don't paint plastic fuel tanks though.

 

[O.J.Didit]

Before you go with decals on a plastic tank you may want to think about this.

Most fullsize MX bikes all have plastic fuel tanks however the early ones with plastic tanks had a problem of decal adhesion because believe it of not the plastic tanks breathe fumes thru them so the decals will bubble up just like your paint did. The initial solution the factory came up with was to punch a bunch of small holes or slits in the decal so the fumes could breathe off. Did it work, kind of.

If you look at all of latest model MX bikes they now have a separate bolt on tank cover or shroud that serves as both a air scoop for the radiator and a graphics mounting surface that is free from the fume problem. The bolt on shrouds are used even on the aircooled bikes with out radiators so they have a good surface for the graphics free of the fume problem.

O.J.

 

[creia]

I can tell you from experience that decals WILL bubble/lift off of a plastic fuel tank.
Michael

 

[Tom S.]

...Caswells does NOT work on plastic. I don't know the type of plastic, whether it's PTFE, or whatever, but even sanded, that epoxy does not stay adhered...

Ducati sold a bunch of motorcycles around 2006-2010 w/plastic fuel tanks that reacted to ethanol in the fuel. I have one. The tanks warp and bubble after awhile. The story was that the engineers missed this because they don't use ethanol in Italy (I dunno if that part's true). There was a class action lawsuit and everyone got a new tank. Most of the new tanks were treated w/Caswell. I'm not sure what type of plastic these tanks are made of, but the lining does stay stuck to it and I've had no problems after several years. I'm also still mindful to use ethanol-free gas whenever possible.

...Most fullsize MX bikes all have plastic fuel tanks however the early ones with plastic tanks had a problem of decal adhesion because believe it of not the plastic tanks breathe fumes thru them so the decals will bubble up just like your paint did...

I've had several old Hondas and Suzukis (both 2 and 4 stroke) w/the OEM graphics stuck right to the tank and they didn't bubble at all. But when the decals got worn and I peeled them off and put on new ones, those new decals would always want to bubble and lift after a short while. I have no idea what they did different at the factory.

 

[Havasu Dave]

I'm not sure what type of plastic these tanks are made of, but the lining does stay stuck to it and I've had no problems after several years. I'm also still mindful to use ethanol-free gas whenever possible.

Tom, the Ducati tanks in question were nylon, and Caswells does adhere to nylon according to several on the web who have used it. I noted was that Ducati owners were cleaning the tanks with Xylene. I've never used it, but I doubt that would have made a difference, since epoxy doesn't adhere to polyethylene types. I have to wonder though, if using that as a degreaser would have made a difference.

Alcohol is a natural reducer for epoxy bases. It is what I use for reducing all types of epoxy from FRP resins and two part glues, to Caswell sealant instead of acetone, as it does not flash as quickly retaining the required viscosity longer.

One more difference is that when you remove the fuel pump on some of the affected Ducati tanks, you can reach in and do some scuffing. In my case, I was relegated to screws in the tank, and the drier on cold for 30 minutes, wrapped in a towel.

On my Cat tank, the Caswells stayed in there for quite a while. Months. I did not realize it had "failed" until my leak came back. The epoxy lifted off an a monocoque structure matching the tank. It didn't slough, peel, or melt. It simply did not adhere. I had to break it up to remove it from the tank. Structurally, it was sound.

That same tank uses decals as well. Vinyl. Never had a problem with them bubbling up either. Of course the same decals have been used three times now, so they're looking worn. But never bubbled.

I wish I could try it again with Xylene, but the bike is sold and going to a new home. Leak was fixed with heat and melted plastic from another tank.

 

[EVOL Tweety Bird]

Dave, this was a tank from an old Manco Thunderbird, as to it's composition, you got me. I had read on the flame treatment, my take was that it swelled the top of the plastic parts/molecules to form a sort of shell, but I would imagine down the road even that would eventually leak through.
I'm familiar with using heat to "restore" plastic trim on autos, getting rid of the dulling that occurs from exposure.

I had considered even glassing the outside of the tank, but then thought if the gas is seeping through I'd probably end up with the glass shell coming loose from the tank.

Looks like for a painted tank I'll end up going metal. Too bad someone hasn't come up with some sort of leak proof bladder to fit into a plastic tank. Oh well live and learn.

 

[Havasu Dave]

Looks like for a painted tank I'll end up going metal. Too bad someone hasn't come up with some sort of leak proof bladder to fit into a plastic tank. Oh well live and learn.

:thumbsup: Yeah, and I tend to get too deep in the weeds on stuff sometimes, but I went through similar pain as you. Those Cat tanks are not cheap, and I tried sealing it several times with various methods. There is probably some obscure Mil-Spec sealant that would work.

I just feel bad for you that you ended up with a ruined such a pretty paint job after so much work.

 

[Dr. Shop Teacher]

I'd actually experiment and try to pull a fiberglass mold off the tank. Then do a cover that's stepped slightly off the plastic original. I, too, tried just about everything on my Manco tank. The vapors shouldn't affect a 3/16" thick 'glass cover.

 

[EVOL Tweety Bird]

You know I could always spend more stupid money, like I haven't already, ut: and just have a fuel bladder built like in the race car.
Split the tank at the seam, install the bladder and glue the tank back together. Maybe right after I win the lottery.:laugh: