Britbike forum Forums British motorcycles in general British motorcycles in general Rusty fuel (gas) tank

Hi all,
What is the best way to get rid of surface rust inside a fuel tank. I have tried some nuts & bolts shaken with some fuel but there seems to be a little bit left. Also is there a way to seal it once it is clean?

There's a few chemicals like evap-o- rust that work well.
If it's not too bad white vinegar will work. I guess I should have started with whether or not the tank is finished. White vinegar won't kill paint immediately and can be rinsed off with water and isn't toxic to dispose of easily neutralized with baking soda. There are probably a few threads on here debating the different tank coatings. Not going there. I have used redcoat and Kreem both eventually failed, possibly from user error. Google search tank coatings and add the word britbike and it ll probably bring up a few threads

How much rust is inside there ?
If its full of pinholes when its all gone, you are on a hiding to nothing ...

Otherwise, have you heard of the ole molasses and water trick.
8:1 is the usual ratio quoted, but it seems to work no matter the strength.
It can get a bit whiffy, take care.

A good rinse out with phosphoric acid when done will passivate it, to some extent.
(the panel beaters 50% strength stuff, SuperCheap Repco etc carry it,)

Redkote seems to come highly commended, but I've yet to try it.
Several projects lined up for it though ...
Hopethishelps.

I've only just taken the tank off as part of the first part of restoration. All of the metal seems ok & there are no dents or scratches. I'm going to respray the whole bike (Inc the tank) when I've finished the preparation. The bike has been in a container for the past 10 years, prior to that my Dad rode it. I cleaned a lot of small bits of rust out with the old nuts & bolts trick but the inside still looks a bit off.

I would avoid tank liner if you can.
It can be more hassle than it’s worth

Electrolysis , used it for several petrol tanks and one oil frame. Works great. I use a washing soda solution as an electrolite. Set up a heavy duty car battery and keep it on trickle/maintenance charge.
Set up a pos and neg electrical connection with some crocodile clips , install an in-line 10amp fuse in one side for piece of mind.
Use a bit of flat steel bar , about 1/4" x 1" x 12"(ish) with a 90 degree bend so there's a good 6 inches horizontal within the tank.
I made a wooden collar for the flat bar so I could jam it into the filler hole and keep it isolated.
Connect tank to neg side.
Set up flat bar and test between tank and flat bar with a multi-meter to make sure there's no continuity before making final connection to battery.
When you connect the positive to flat bar you'll see a few light sparks, this is correct and shows you have the circuit good, if the fuse blows you haven't got the flat bar and tank isolated properly.
Remove and clean flat bar every few hours, but can be left overnight when you need to.
Keep running for about 24 hrs and then change for fresh electrolite solution.
Run for another 24 hours , or as long as it takes.
Flush out with clean water , dry out , I use my shop vacuum in reverse set up so it's blowing warmish air through the tank.
If you want you can rinse out with 50% strength phosphoric acid x about a gallon to passivate the surface and then rinse again with clean water. Dry and rinse with an oil solution.
Works great and you'll be amazed at what comes out, very effective way to remove the rust, just needs some patience,i.e. a couple of days.
I used an endoscope for interim and final inspection to see if it was clean enough.
Plenty of info on Google about the process.

i had success with white vinegar filled tank with it sit a couple of days poured it out have heard other folks used coke.......uh coca cola.. and even mole-asses

What you do will depend upon what you intend to do with the bike when finished
My tank is very rusty and I do nothing with it because I ride the bike at least every month if not every week .
Aussie fuel north of the Murray does not usually contain oxygenators as US & UK fuel does
Rust needs an oxidizing agent , usually O from water .
However if you keep the tank full then the only problem will be the odd build up on the fuel filter and even finner mud in the fuel banjo
People go mad to remove rust and most cases they leave an activated surface which rusts even faster and you end up in a self feeding loop ending up with pin holes or a tank liner that contaminates the fuel, goes soft & blocks the carb or lifts off the bottom so provides a little pocket for condensed water to sit in and create havock.
If the bike is going to sit unused for decades then the molassas or any phosphate treatment will be fine as all of them leave a passivated surface that needs to get really wet to continue to rust further
Any acid treatment HCl , Citric Acid, Vinegar etc etc etc will leave an active surface that will promote rust if not passivated .

Head & shoulders above all of the tank treatments is POR 15
Nothing touches it apart from UV rays and if you are getting UV inside your tank then you have other big probems
Down side of POR 15 is it is a complicated process that has to be done properly because if you stuff it up the only way to remove it is to put a long wave UV lamp in the tank for hours, then abrade the chalky surface then repeat till you get back to bare metal .

BEcause motorcyclist are lazy, stupid, cheap & impatient a host of vastly inferiour treatments that can be done overnight have emerged, none of them are worth doing but people use them because they are quick easy & cheap .

BSA, you last paragraph states most of the problems motorcyclists cause themselves.

Everyone,
Thanks for your input. To answer a few questions, my main aim is to restore the bike as well as I can & then ride it as often as possible in club rides etc. It will be the only complete bike I have untill I start work on the other project.

Well considering there is a Newcastle Vintage club, A Newcastle Classic Club. the Coalfields Classic Club & a sort of branch of the BSA club in your neck of the woods that would be a lot of riding oppertunities .
Give the tank a rough clean & keep it full of fuel
Do not use e-10 so it will have to be plain unleadded or premium
It should not be a problem
A plain phosphoric acid passivation should be all you need
The tank on the M20 was badly rusted from poor storage back in 1991 when I got it .
So it got a hot soapy wash, a caustic degrease then a hot rinse followed by a dilute HCl wash
Since then nothing has been done to the tank and since 2010 it has had to live outside occasionally under a bike cover .
It really should get another good clean but I have way too many other things to do
About every 3 to 4 months I pull the fuel tap to clean the outside of the fuel filter, drain the tank and filter out the rust , clean the banjo & filter
Sounds like a lot but really only about 1/2 hours work.
People who do not understand metals freak out about things like rist because their cars get rusty & fail rego inspections
But fences & car bodies are not fuel tanks and even considering the salty coastal air at Wangi Wangi once the flakey rust is gone your tank will be fine so long as it is kept full of fuel and occasionally drained to ensure there is no condensed water in the bottom.
Steel needs a galvanic potential + an electrolyte + an ozadizing agent to rust
Keeping the tank full of petrol removes 2 of those 3

I used Caswell Epoxy on two tanks. I have heard problems with the Kreem coating peeling off. The Caswell sealer is very tough and stuck well after I did the nuts and bolts sloshed around, then the electrolysis described above. Instead of a battery I used a battery charger set on two amps charging. In the US the washing soda is 20 Mule Team borax. Worked very well.

Hi all,
A quick update. After cleaning with the nuts & bolts trick I put 16 lites (4gals) of white vinegar in the tank & let it sit for 3 days, shaking it when I walked past. You would not believe the amount of flakey rust that came out & in some cases you could see clean metal. I think about 90% of the tank is clean now. I decided to use the same solution on the exhaust pipes with a bit of elbow grease & they look remarkably good. Thanks to everyone for their input.

As you say, a soak in white vinegar for three to four days will usually do the trick for removing rust from steel or iron parts.
It will also strip off old zinc plating as well.

Best of all, vinegar is CHEAP, and as a "natural" product, is bio-degradable.

Give the tank a hot caustic soda rinse before you use it to passivate the now quite active clean steel surface

My preference is to use citric acid, you can buy granules of this stuff on eBay for not much money, home brew shops are also a good source, I like to use around 100g per gallon of tank.

Clean the tank out first using nuts and bolts shaken around and then de-grease the tank with hot soapy water.

You will need to dissolve the citric acid in a pan with enough water to fill the tank. Keep the pan heated and slowly dissolve the citric acid until its all gone.

At this point, you should have available some bungs to fill the petrol tap holes and filler cap. The home brew shops usually have a selection of rubber and cork to fill these holes so buy in advance.

Once the holes are bunged pour in the citric acid all the way to the top and add the filler cap bung.

The de-rusting process takes anywhere between 24-48 hours, after which the citric acid can be discarded.

The tank should be clean inside but avoid rinsing with water as it will flash over with rust instantaneously.

I like to rinse the tank inside with a 250ml bottle of 81% phosphoric acid "PH Down" available from hydrophonoc suppliers on eBay see This Example
, this adds a protective phosphate layer, be sure to let this layer dry for a day or so.

If you wanted to add POR15, this would be a good time to do it.

The advantage of all the chemicals mentioned above is that they are pretty much tank safe and wont ruin your paint.

Citric Acid granules are available in the “baking” section of your local supermarket. Enthusiastic cooks/bakers use it to add a lemony, citrus tang to various recipes. No need to get fancy with eBay or home brew shops. It’s just an item on the weekly supermarket shopping list.
Using it around the average household with small children, pets, grandchildren, etc, presents minimal hazard. It’s also no drama to dispose of.
I use it as a ‘pickle’’ after Silver soldering small objects. Silver solder does a particularly neat job on vintage fuel lines plus allows you to safely nickel plate them afterwards if need be.
I’m not keen on having hazardous chemicals such as caustic soda in my workshop plus disposal after use can be a problem.

Mine too. It's the shizzzz

Thanks everyone, it is great info. I've started to clean the old mufflers after leaving them in the vinegar for a day. You can see the results in the attached photo, I can only fit half of the muffler at a time.

wunderful!

Tip it down the toilet ! *
Does a wonderful job of cleaning out all those pesky tree roots and grease out of the drains.
Buying 'drain cleaner' is EXACTLY the same stuff. (at x times the $$s)
And is the basic primary ingredient for soap, laundry powder and dishwasher tablets...

Nice job on the vinegar.
Commercial phosphoric acid (50%) does the same job, in mere minutes.
Its the primary ingredient in Coca Cola, so not exactly 'hazardous' either...

* settle out the lumps and gritty stuff first though (in the caustic, in the caustic !)

Once again you will need to passivate the surface or it will rust again right in front of your eyes
When finished give iy a heavy coat of chrome WAX note wax & not polish.
Chrome plate is microcracked , looks like a clay pan after 5 years of drought
Wax fills up those voids , polish does not .

Nice clean engine oil does a pretty good job of this too.
(hence 'oily rag condition').

Might smoke a bit when you go for a ride.
A wipeover with a clean dry cloth beforehand will minimize this.
Once the oil is charred down in its microcrack hidey holes, it will be waterproof and rust proof for eons...