Rusty Fuel Tank on 1959 Model 50

Mike. You have to combat the rust which ever course you take. You cannot line a tank without first ensuring that it is totally rust, grease, dirt and of course petrol free. If the rust is loose and flaky you need first to remove that. A method often used is to put a large handful of old nuts and bolts into the tank, and shake it every way you can until all the loose rust has become displaced, then carefully empty it.

My preferred method for the next stage is to convert the rust, by using a phosphoric acid solution, which is readily available to purchase on-line, if not locally. Google it and you will find a choice, no doubt with instructions.

Once rinsed with water and immediately and thoroughly dried, you can either go for lining, or not. If after the above process the inside is solid and sound, I would not personally line the tank. Unless you carry out the job absolutely perfectly, it will fail. If the tank has gone thin, or even perforated, then you either get the poor metal cut out and properly repaired, or you line it. Which one you use will no doubt be the subject of further replies.

I am a little surprised that you are having the tank shot-blasted and powder-coated. I hope you don't mean shot-blasting. It may be suitable for tractor chassis', but not ideal for sheet metal, which will be damaged. Use a very fine blasting media if you must, but how are you going to keep it out of your tank? A bolt and washer in the petrol tap hole no probs, but how are you going to seal around the filler? That needs to be paint-stripped too, and the last thing you want is to get any media in the tank. You would have to scrupulously clean it out afterwards; not as easy as you may think. If any of that gets into your engine, it is game over.

I would be inclined to Nitromors the tank, prepare it in traditional fashion, and wet-spray it, for a much better and more authentic finish.

Ian

I powder coat everyday running tanks, the finish is not bad but durable. The media used to prepare the tank will get into the tank however well it is bunged and masked so I always clean the tank out but also fit fuel filters in the feed to the carbs to collect whats left. You can internally derust the tank before powdercoating with citric acid or phosphoric acid. The phosphoric acid will leave a mildly anti rust coating of iron phosphate and for this reason is used a lot by powder coaters themselves after blasting.

As for sealers they are best left alone, they are all described as resistant to Ethanol, none are Ethanol proof which means when it fails you have no recourse.

I've used both the sealants sold by RGM and Frost's POR15 without problems. I have never had them break down or dissolve and cause problems with the carb - 10 years in the case of RGM's sealant.. A rusty tank however will cause constant hassle as rust invariably gets past filters - the only thing that seems to stop its progress is the main jet!!! The tank should have a few handfuls of nuts and bolts or nails thrown in and an evening spent shaking it about to dislodge the loose stuff. Then a really strong hot alkaline detergent or even caustic soda (do not add this to hot water! It's exothermic - read up about it first) and left overnight. Then a rust treatment such as Frost's metal prep. Once thoroughly dry then add the sealant and run it around the tank and empty the excess out and allow it to thoroughly dry - upside down preferably - this will stop it pooling in the seams which could leave you with uncured sealant which WILL be affected by fuel. Incidentally, featherbed tanks are b******s for rust in the bottom seams - try and scrape out any rust here with a piece of stiff wire. The whole job should take you around a week to get everything cleaned, dried and cured - do not be tempted to rush it.

Regards,

Ian.

One thing I forgot to add - the sealant should added AFTER the powder coating - if that's the way you go - the parts to be coated are heated to >200?C!!! That's hot enough to melt soft solder and will wreck any sealant.

Regards,

Ian.

Previously mike_haworth wrote:

Probably a subject that has been discussed a lot, but please bear with me, I'm new to the game. The petrol tank from my bike is due to be shot blasted and powder coated but the painter has raised the issue of internal rust. Although the tank doesn't leak there is a rust problem that needs addressing. The guy rebuilding my engine ( a very experienced restorer who has had bikes on the front of Classic Bike) is very much against tank sealers as he claims they ultimately disintegrate and cause carburation issues. Other people I've talked to fully endorse the use of tak sealants. Which way do I jump ?

If I don't go for a sealer then how do I combat the rust ?

If I do go for a sealer, which one ? Old Bike Mart has a number of advertisers (Tank Care products, Tank Cure from LB Restoration Services, Petseal, Tapox). So my quetion is: Sealer or No Sealer ? If Sealer, which one ? If No Sealer, what other solution ?

Many thanks in advance for any useful input.

Mike

Hello Mike, First you need to sort out the rust. There is a new family of rust removal products: in Canada called Evapo Rust and I've seen it advertised in the States as Metal Rescue. Non toxic, no acid and safe to handle. This stuff has changed my life. I'm sure you will find it under another name in the UK.

For gas tanks or any motorcycle parts and hand tools; non-distructive and takes it down to the bare metal. I speed the process by scuffing a bit with a stainless toothbrush. With gas tanks I help it along with a handful of screws and shake the tank around from time to time. I find too that since it is water based several cleanings with kerosene first gets rid of gas varnish inside an old tank so it can attack rust faster. 3 or 4 days and perhaps a half hour of effort and the tank is down to bare metal.

and no risk of eroding the metal with acid.

Once rust free, I too, am hesitant to seal the tank. I've read every specification and the latest generation of sealants claim to be ethanol proof...and I dearly hope they are right.

I don't resort to the stuff unless I actually have a leak; the thought of it failing some day and sluffing off inside of the tank worries me.

That said, everybody I know uses tank sealer plastic coating from time to time. (As much to glue down rust as to seal the tank.)

A fellow I was talking with recently used a DIY zinc galvanizing kit to galvanize the inside of his late 60s Kawasaki gas tank. Looked great. Seems like an interesting idea that might warrant some research.

Regards, Grant MacNeill, 51 ES2, Toronto

Interesting Grant! Rust is iron oxide, I wonder what dissolves it if its not acidic? I experimented with one tank and did the usual shaking with a hand full on nuts and bolts then I filled it with Tesco (other brands are available!) value diet coke and left it for about a week, worked a treat and the contents could be poured down a drain. on another I used milk stone remover from an agric supplier and diluted it 3:1 (its strong phosphoric acid) that did the same job in an afternoon but I had to neutralise it with about a lb of bicarb!

electrolysis is another option, but the big risk is flash rusting after you have washed it out, the trick is a quick rinse then flush out with isopropyl alcohol which combines with the water then dry with a hair drier/hot air gun and swill it around with some oil and petrol to coat the inside.

Previously grant_macneill wrote:

and no risk of eroding the metal with acid.

Grant. No need to panic at the mention of acid! Phosphoric acid will not even harm paint, let alone sound metal. It simply neutralises the rust and converts it to a rust resistant coating, as previously mentioned. Neither is it a hazardous chemical like caustic soda. You drink it whenever you have a Cola..... You can also store and re-use it.

Given that it is cheap, and proprietary potions are invariably expensive, I would not look for anything else to treat the rust.

With regard to blasting and powder-coating petrol tanks, I know that people do it, but I personally would not, for the reasons mentioned. Why knowingly introduce an abrasive grit into your petrol tank, when there are other methods, which will also provide a better finish? Cheaper and easier? Blasting and powder-coating is fine for frames and cycle parts; unless it is a particularly historic machine, where authenticity is paramount; but ask a chrome plater what he thinks about blasting sheet metalwork such as a petrol tank. The surface gets damaged and pitted, and sometimes no amount of linishing will restore a finish suitable for chrome plating, and the metal of the tank gets thinner in the process. You will be relying on the thickness of the powder-coat in an attempt to provide a smooth finish, and it never looks right, imo.

Just my two-pennuth!