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Treating, cleaning and painting the interior of a motorcycle petrol tank

I hope that this may help someone now or in the future.
I treated both tanks of my M20 and my BMW R51/3 and all is still well and stable.
Clarification: A distinction must be made between an internal coating for the purpose of returning the tank to its original condition,
i.e. painted on the inside so that it does not rust, which I describe here, and a coating that is supposed to clog small holes.
If the latter is performed - it should be applied only after we have performed the first step, i.e. color coating, as detailed below.
All materials (except the material itself- the paint) can be purchased at your local DIY stores.
The ingredients:
The paint, or inner coating:
Excellent material can be found at Mark Huggett, Switzerland: The part number should was: 16 114 080 042 Y and it refers to 1 liter. The material is dark red based on lead and mercury. Excellent stuff. Please note The volume of your tank so that we do not find ourselves with too little material.
Thinner (21 grade at least) or any other quality solvent.
Liquid dish soap.
A handful or two of small pebbles or any other granulat.
A handful or two of sand.
A handful or two of Old nuts and bolts (optional...).
Mixed hydrochloric acid - 2 liters.
Hot water (very hot).
Acetone - 1 gallon.
Grain caustic soda

The tools:
A pair of hands.
Face mask or nose / mouth cover separately and goggles separately.
Air pressure for ventilation and drying of the tank (I use a compressor to inflate small children's pools).
A good flashlight.
Ordinary and cheap work gloves (combined leather with fabric is ok) - not required.
Disposable gloves for latex or similar - optional.

You should try and take a day off for this job because there are sections in the process that require drying time.
Hazardous substances are also involved in the operation, therefore: I remove all responsibility from the execution process described here and its results and consequences bla bla bla.
Everything written here is a recommendation. It is my way to do it and I'm sure there are more others and better ways bla bla bla, again.
Work when there are no children around and when they are not expected to arrive.
Work in a well-ventilated place.
Keep flammable / explosive materials away.
Keep matches away and do not smoke!
Keep animals away.
Keep your mother-in-law away (don't ask me way).
Any bodywork on the tank that requires heat, soldering, patching, tapping or drilling - should be performed before this treatment.
After that do not perform any work on the container except for external paint.
Like everything in life: the quality of work is directly determined by the quality of the surface preparation, so you need to invest in the preparation of the tank. This will ensure that the paint can really stick to the sides of the container and stay there for a long time.

Note: There is a reasonable chance that the exterior paint of the container will be damaged during the process because it involves acid, thinner, heat, etc.

The process:
Empty and dry the tank of fuel. Plug all openings except the filler opening. Put the nuts, screws, sand and gravel into the tank.
Put on earplugs and start shaking well in all directions (excellent exercise for hands and shoulders).
The purpose of the process is to release loose rust or peeling paint leaves.
Then empty the tank and rinse well with warm soapy water.
Now wash out the soap well! Put on the face protective equipment and gloves on the hands. Pour in the thinner, mix carefully and pour.
Note that any material in this process should come in contact with all sides, including the tank ceiling. How to do it? There is no particular method, just work carefully!
Rinse the thinner with very hot water and dish soap. Rinse the soapy water well. Pour a little cold water (meaning regular from the tap) in and carefully add the caustic soda.
A chemical reaction will begin immediately and the water will heat up. The tank will heat up as well so we are with gloves now.
Immediately shake the container so that the caustic grains dissolve well - otherwise they will become a single piece and will not disintegrate well (we want to prepare a solution).
Gradually add the rest of the cold water and mix carefully each time, so that a uniform solution is formed. Fill the tank to the brim with water.
Wait several hours, depending on the condition of the container. I waited more than 3 hours on my M20.
Pour the solution, startle when you see what comes out and rinse well with clean, warm water.
Shake and pour. Rinse again with warm water well. Care should be taken to wash away any soap residue, as it will prevent the hydrochloric acid process which is next in line:

Drain as much of the clean water residue as possible. Pour the hydrochloric acid in (carefully) and mix inside the tank.
If there is a lot of rust - there will also be a strong reaction with hydrochloric acid! Caution!
The fumes are just awful so we are with face protection here.
Do not shake the container but mix gently. The acid should only touch the wall and not be thrown at it.
I performed the entire cleaning process in the shower in case of spraying the materials.
Light in with the flashlight and make sure there is no rust left in the corners, seams, etc. Empty the tank and rinse well with warm water. Basically the tank should now be with clean, gray and exposed metal sides.
Now you need to work fast, so it is highly recommended to prepare everything necessary in advance, including a tidy place, air pressure, etc. The clean metal oxidizes immediately, and rust can appear (visually. In fact it is already there within a minute) already after 10 or 20 minutes, so the importance of speed of work.
Pour the acetone into the container and shake. Acetone is a rather aggressive material and care must be taken not to attack or corrode the caps of the container, which should be built ahead of time from a metal or plastic material that will be resistant to acetone.
Disassemble the caps and open all the openings. From now on you work in the sun (preferably the scorching summer months).
Dry the container well in the sun and with the help of a heat spreader or some air pressure. From time to time turn the tank over and ensure that the hot air reaches every corner.
Once you are sure that the tank is indeed dry (check with the flashlight) - you can go to the paint purring stage.
It is very important that it is completely dry!

The tank is plugged again except for a main filling opening.
Important: If the tank has a lower opening (sure there is a fuel outlet opening for the tap) and needs to be plugged, then immediately plug a stopper made of a long screw (in the case of a female thread) that protrudes above the surface inside the tank to prevent material buildup and clog there.
The long screw that will serve as a stopper should be coated with a little Teflon (white plumbers tape) and then screwed in.
Make sure it is above the surface inside the tank.

In the case of a male thread - it is advisable to insert a pipe of the appropriate diameter, or a cork or anything else that will seal and protrude above the surface of the inner floor of the tank.
Pour the paint according to the manufacturer's instructions (need to mix before?) And start rotating the tank in all directions and angles to ensure even spreading. The material usually hardens quickly but remains viscous for a long time,
long enough that it will still collect at one point if we do not invest in rotating the tank properly, with a lot of patience.
Once you are sure that the entire interior of the tank is well painted, the excess paint should be poured.
Do not be tempted and go captive after thinking that much is good! This is not the case!
A lot of paint will not dry well and will also start to crack over time!
Pour off the excess and place the container straight on the floor. After 5 minutes again pour what has accumulated and place the container again, this time on its side. Pour leftovers again after about 5 minutes and place again, this time on the other side and so on and so forth, until the container rests on all sides, including the bow and tail.
Allow the paint to dry according to the manufacturer's instructions. That's it.

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Re: Treating, cleaning and painting the interior of a motorcycle petrol tank

Thank you Michael! that is very useful.
I have copied, pasted and saved it.:+1:

I looked it up on the website and found (after a bit of a search) this :

Article Details: 16 11 4 080 042.X
No image available Part #: 16 11 4 080 042.X
Description: Tank coating red-brown matt, 0,5 ltr.
Price per piece (CHF) excl. VAT: 32.53

that's in Swiss Franks btw.

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Re: Treating, cleaning and painting the interior of a motorcycle petrol tank

It could go into the 'Technical Section' as a reference piece...Ian

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Re: Treating, cleaning and painting the interior of a motorcycle petrol tank

It will flatter me, but with your permission, if that happens - I would be happy and thankful if it will be proofreader and error corrected because English is not my native language.
I can see some already.
Thanks in advance.

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