On Tank Lining

From the Caferacer.net board:

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:

http://www.boatus.com/seaworthy/fueltest.asp

[...]
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!:
http://egyptian.net/~raymacke/Cbnskif27.htm

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

matt

Thanks, Matt!

Cleaning up the top mold

OK, Now I'm cleaning up the edges of the mold and am holding it together with some old 5mm machine screws I had:



I left about an inch of overhang where final top piece will be glued to the bottom. Gonna be hard to reach in there and get the glass applied well. Especially if I want to vacuum bag the layup. I'll probably carve out some foam blocks that will fit under the overhang which will apply some compression once I pull the air out of the bag.



Sarah has grown a little dubious of all this work entrenched in my subconscious.

Snap, Crackle, POP!

OK, well I built up all the other facets much like the first and this morning used a butter knife to pry them apart. It's quite a noisy affair as the PVA releases the fiberglass from the mold popping and cracking. I had to rap on the outside with a wooden dowel to help release some areas. Sarah didn't like that at 5:30AM.

One trick I used to get started was to lay down a few pieces of packing tape on the opposing side of the flange being erected, followed by a bit of PVA. This allows you to tug the pieces apart a bit.

Anyway, here is how they look!



The "Locating Dimples" I cut with the drill bit really help in lining this thing up; glad I took a few extra minutes to do them. That one hole you see was where I actually went all the way through on the drill so I had to cover it up with tape.



This thing will get some bolts to hold it all together during layup. I'll trim the interior overhang down a bit from what you see here, but this is still going to be a very challenging layup to execute. I think I'll have to cut the handle off of the chip-brushes that I use to apply epoxy for a little extra maneuvering room.

Begin layup on top 2

After the glass had cured, I tried pulling the weirs used in it's construction. Sadly the adhesive from the glue gun stuck a little too well to the plug. I guess I got carried away with the glue and used a lot, figuring it'd just peel right off but it didn't!

Ended up tearing some of the skin off the plug in the struggle; so i patched with a bit of smooth packing tape. Next time, I might attempt covering the entire plug in fiberglass beforehand as a way to toughen up the skin.

Anyway, I carried on with the other side, this time just using a few small dollops of glue to hold the weirs onto the plug.

I cut a few depressions with a 3/8" drill bit into the opposing flange there (marked by arrows) so that the two sides of the mold have a means of orienting themselves neatly.

Top mold layup 1 complete

One step at a time! I used a slurry of milled glass fibers and epoxy to get into the nooks and crannies before doing the primary layup using 10oz fabric. Used a bunch of small rectangles of glass in a patchwork so that they'd lay down okay along the weir. Fingers are crossed.

Is this thick enough?

8 layers of 5.6 oz "S" glass ends up being roughly 1/16" thick. Hmmm...I'd like it to be about twice as thick just for peace of mind but just 8 layers feels awfully tough.

I can bend this sample about 1/4" with my bare hands; certainly couldn't fold it without a vice and some pliers. But is it enough?

Addendum A user going by the handle 'monkey' frequents the Caferacer.net forums who does a lot of this stuff professionally. His current race tank build up process just uses 3 layers of 200g Carbon, and thinks this is more than enough, even 'gnarly': http://www.caferacer.net/forums/topic.asp?TOPIC_ID=9756

weirs erected for first section of top mold

So I'll apply glass/resin to the mold and a ways up on the weirs to build some flanges for the mold pieces to bolt together with. This thing has a coat of PVA that is drying for an afternoon layup.

I learned this trick of roughing out a complex curve from a guy who build a gas tank in a similar way on Bay Area Riders Forum. Reminiscent of differential calculus in a way, but there's nothing some old junk mail cardstock and a glue stick can't do



Once the patterns are made, I just transfer to some tougher card board and then cut out and seal with packing tape. Few minutes of hot glue gun action later et voila

bottom popped off

OK, bottom jumped off of the plug no problem, now time to start on the top mold.

by the way, this is gorge

Taken from the Street/Flat Tracker thread on ADV Rider: http://www.advrider.com/forums/showthread.php?t=272954

bottom still curing

Left the assembly in the bag overnight but it was fairly set by the morning. Carefully peeled off the breather cloth and peel-ply without tearing the part off of the plug because I want it to cure a bit more for the next day or so. You can see the peelply-breather cloth just in the background, it took up a bit of the excess resin so that's good. Looks like it'll be okay, tho I don't like seeing the wrinkles along the channel there:



I'm not sure 8 layers of 5.6 ounce "S" glass is enough so i'll to an experiment with 8 layers of 3"x3" squares just so I can cut into them and see how thick it really is. Yeah, shouldda done this beforehand...got ahead of myself. bladdeeblah.

Bottom layup begun

OK, well the last 2 hours seemed hopeless. 8 layers of 5.6 oz "S" glass later and the bottom layup has begun it's cure in the home brewed vacuum bag. The pump (yup, that's made from a cheap bicycle pump that's been bodged to work in reverse) came from a fellow's idea on the instructables.com website:

layup schedule

Here's a rough outline of how I'm thinking the parts get built from the plug. This is a cross sectional view of the assembly.

• (A) Here you can see the plug (defined by light cross-hatching) with the female mold pieces laid up off of it. Notice the flange on top: the female mold will have to be made into several parts to prevent it from mechanically locking in the plug.
  
• (B) OK, once the plug is removed, I'll do a lay up of the final part for the top of the tank, outlined as black
  
• (C) The bottom of the tank will just be molded directly off of the plug since that should in theory fit exactly to the bottom of the top part.
  
• (D) Then it's just a matter of assembly. HaHaHa!
  

This is just one cross section! It get's trickier to render what this thing will look like at the front and back but they'll have a similar "overhang" built into them. The top mold will actually be made from 4 pieces because of the overhang, but the concept is similar to what you see here.

wax, polish, repeat

after going to 600 grit wet sanding, this plug's ready for some parting wax. I'll get a few more on there before doing a layup of the mold.



That nubbin on the top will be where the gas cap goes. Looks kind of clunky but i could hardly give a shit right now.

I made it by forming a ring out of glass on this cylinder I made out of paper wrapped in packing tape:


Then attached the ring to a layup for the top like below; you can see the fuel cap in the background there; it's a nicely machined vented unit i got from a home-built aircraft supplier