Tank lining with composites seems to be a hotly contested subject of late especially with ethanol based fuels. I've read about several treatments. The most noteworthy ones to date are:
- POR-15: This is a paint on substance. I first learned about it from an epic moto tank building thread on Bay Area Riders Forum.
- Caswell: A two part epoxy based treatment designed specifically for ethanol fuel resistance. One source on the Bay Area Riders Forum has had a lot of experience with both POR-15 and Caswell from running a painting business and restoring 100's of moto tanks. He swears by the Caswell. I'm inclined to agree because it's epoxy -- hard to beat it for adherence and toughness.
- Fuel Safe: Manufacturer of fuel bladders for racing appliations. You send them a copy of your plug and they build you a physical bladder that I guess is just draped into your tank "shell". Probably bucco $$ but also probably the best.
- Kreem: This has been around for ever and is widely regarded as garbage by people who've used the other products. I guess it doesn't bond as well and ends up delaminating from the walls of your tank. ick.
There's a lot of discussion among the boating guys, too. I picked up on an article below from a post on the ADV rider forum. Frustrating that the study does not give specifics on when it was conducted, what epoxy was used specifically in this test, nor what kind of lining was used:
Finally, chemical resistance data from a leading epoxy supplier showed that even epoxy can be attacked by ethanol. The test was made using the company's most resistant epoxy and exposing fiberglass lab samples to 10% ethanol gas and regular unleaded gas as well as diesel and aviation gas. The results for the ethanol gas showed a 10% loss in hardness and a 10-15% loss of compressive strength over a 16-week period and it’s likely that the loss of hardness and strength would continue to fall at a similar rate. The unleaded gas, diesel, and aviation gasoline tests, none of which contained ethanol, showed virtually no loss of strength.
What to Do?
Many boaters have made the decision to replace what were thought to be superior fiberglass gas tanks with aluminum tanks (tank replacement is not covered by insurance). Seaworthy has talked to resin manufacturers who say that there are resins that resist ethanol, but simply coating a tank with one of these resins is not likely to work, since the tank has to be thoroughly cleaned and prepped on the inside and the resins have to be specially cured.
Actually from the article at the top,there's a link out to some boat builder's own empirical test with ethanol vs epoxy using the caswell jizz as a barrier. It is not terribly promising.
But I am dubious of anybody being able to get a good result from a composite tank that has already been in service!:
From that same thread on Caferacer, Matt (sign-on 'monkey') who's a very well regarded moto tank fabricator had this to say:
as far as a tank lining... epoxy works better than anything.
the problem with most linings is that people are appling them after the tank has been made or even used... good luck getting whatever you are pouring into the tank to bond with the inside surface and actually last for more than a few months.
once you have both skins of the tank prepped for bonding together...
1. make sure all your fittings are set ( much easier to install things such as caps, inserts for petcocks etc etc before you bond together).
2. sand the glue surface with 80 grit so you get a good mechanical bond... also sand the entire inside surface ( for resin coating)
3. i then apply epoxy resin to the inside faces ( usually 2 coats ) and let it tack up for an hour or so. i also apply the epoxy adhesive at this time. with the flow coat and the adhesive ( on the glue surface) tacky... they stay put when you are handling the tank halves rather than ooze all over the place
4. align and stick together.. use small spring clamps to hold bonding surfaces together. once happy, i then pour a few ounces or catalysed resin into the filler hole to seal any potential leaks.
then the tank is then placed on a level surface to cure.
5. come back after resin is completely cured and machine edges for neatness.
6. cleanliness, clean hands, lots of gloves, masking tape... etc etc
Make sure to get a vented fuel cap or you will get vapor lock.
now this all sounds easy.... but it is not fuel tanks are a pain, if this fails on you while you are riding.... major problem
my father in law made one for himself in the 60's and it split at the start/finish line dumping fuel all over his running bike.
it was my goal to prove to him i could successfully make them and race em. i will never be on the racetrack without one... except my crf 150... leaving it alone. your glass wont be too thick.. i just want my tanks to be significantly lighter than stock... otherwise why bother? my goal is to always make them lighter than 2 lbs.
Just a reminder.. i have been in the composites fabrication business for over 11 years... building everything from custom sailboats, custom offshore racing sailboats, lobster boats, America's Cup parts.... the list goes on and on... i always love when people try to get me to give em a crash course in this stuff and think they are going to make money off of me... sounds big headed.. but it is funny. i started building bike parts when i didn't have the money to go out and buy it... so make it better and suit my needs.
also... if you crash... any tank can potentially crack... steel, alum, glass... if you are concerned about things breaking... run a 1/2" thick steel plate tank... then you'll be fine
from the pics on your post... you are doing perfectly fine.
have fun and good luck