Fuel Tank Turning White

[cmc84]

Hi all, mentioned this elsewhere, but I'm keen to get a solution - I have a plastic tank for my Sherpa which no matter how I try to clean it, dries with a white powdery appearance. Have tried paint thinner, car polish, kitchen cleaners, petrol and hot water (not at the same time) but no luck. Had a go with some wet & dry tonight which has almost completely smoothed out the texture of the tank, but still hasn't got rid of the white.

I'd like to have a good looking tank, but I'd rather clean this up than buy another.

Any ideas?

[monty_jon]

Sounds like its faded, probably nothing you can do other than buy a new one

[pschrauber]

To post a procedure that might help without close up picture is difficult.

This might be very small "scrathes" from the snading process, they show up even faster as darker the plastic color is.

There are two possibilities to get rid of them:

1. method:

1. first a polish with brass polish,

2. then again a polish with silver polish.

The basic principle behind this is to substitute deep scratches with shallower and shallower ones, this therefor will only work if you have already used the fine wet and dry sandpaper (1200) befor. Normally starting with 600 then 800 then 1200.

2. method:

If you are really keen in stripping paint with a heat gun, then you can skip 1. and 2. and melt the surface just a litle bit but this works only if you are really very very keen, (I personal had so far only good results with this procedere with smaller parts, so I have to take the elbow grease method).

Just to note there should be no gas in the tank and the tank have been vented for at leat 24 hours storing him upside down with open gas tap!

If the tank is discolored by sunlight or gas then this method will not help completly, discolering from gas is inside the plastic and discolering through UV you will find also som My inside.

[nigel dabster]

To post a procedure that might help without close up picture is difficult.

This might be very small "scrathes" from the snading process, they show up even faster as darker the plastic color is.

There are two possibilities to get rid of them:

1. method:

1. first a polish with brass polish,

2. then again a polish with silver polish.

The basic principle behind this is to substitute deep scratches with shallower and shallower ones, this therefor will only work if you have already used the fine wet and dry sandpaper (1200) befor. Normally starting with 600 then 800 then 1200.

2. method:

If you are really keen in stripping paint with a heat gun, then you can skip 1. and 2. and melt the surface just a litle bit but this works only if you are really very very keen, (I personal had so far only good results with this procedere with smaller parts, so I have to take the elbow grease method).

Just to note there should be no gas in the tank and the tank have been vented for at leat 24 hours storing him upside down with open gas tap!

If the tank is discolored by sunlight or gas then this method will not help completly, discolering from gas is inside the plastic and discolering through UV you will find also som My inside.

You do know he is refering to an unpainted plastic tank scrab?

Edited May 30, 2011 by Nigel Dabster

[toofasttim]

You do know he is refering to an unpainted plastic tank scrab?

Easy there Dabster...

[triple_x]

Hi

I have the same problem with my plastic tank on the 198a.

I'm getting it resprayed but before it is prepared for painting the inside is being lined with a two pack flexible resin that will seal the internal surface of the plastic.

This will stop the vapour bleeding through the plastic and either lifting or fading the top coat.

One of my suppliers whose business is rota moulding (the process used to make tha tanks) told me that the early plastic allowed the petroleum vapour the bleed through. Current formulation stops this(as is obvious the green and red petrol cans).

When finished I will keep the painted tank for display and will use the pattern tank purchased from Bultaco UK.

Whilst on the subject of the replacement tank it is wider than the original by about just over 25mm, this is more obvious when in situ as the frame has much more clearance than the factory tank.

Hope this helps

Martin

[pschrauber]

Hi

I have the same problem with my plastic tank on the 198a.

I'm getting it resprayed but before it is prepared for painting the inside is being lined with a two pack flexible resin that will seal the internal surface of the plastic.

This will stop the vapour bleeding through the plastic and either lifting or fading the top coat.

One of my suppliers whose business is rota moulding (the process used to make tha tanks) told me that the early plastic allowed the petroleum vapour the bleed through. Current formulation stops this(as is obvious the green and red petrol cans).

When finished I will keep the painted tank for display and will use the pattern tank purchased from Bultaco UK.

Whilst on the subject of the replacement tank it is wider than the original by about just over 25mm, this is more obvious when in situ as the frame has much more clearance than the factory tank.

Hope this helps

Martin

This sounds interesting,

I have heard about a simmilar process called "Fluorination Barrier Treatment" but with different indigrents, that is used for plastic containers, but only available in the U.S. so far as I know:

Flouroseal

There where already some gas tanks prepared with this treatment with good results. The treatment was done for old KTM bikes from the 80's to 90's, they have this bright white gas tanks that very fast get colored by UV and premix gas vapors, looking "not so good".

A big pitty is the "coloration" from the gas vapors because it's not only on the surface it discolors the complete material. Gas tank with coloration from premix:

I was therefore a little bit suspicious about doing a paint job to a used tank, when there is discoloring also inside the plastic material there should be oil components also inside, this can effect the adhesion of the paint. I found an never used gas tank for my KTM but it was shaded by UV light and had a light brown-yellow coloring. Luckily only one the surface.

Because I did not want to paint the tank I used the preparation with cleaning, sanding and polishing already posted before. Here a pic after I had done one side without the last polishing, (a 4h job so far):

Mounted:

The result is very OK I think, (By the way the sidepanels got the same treatement). Here another picture with the already done gastank and the radiator shroud where I haven't done any surface refurbish so far, (pic was made for getting replica decals done for the bike, these shown there are samples/try outs and the smaller one's are not the right ones too as I figured out later):

Back to the Bultaco:

I just repaired the airbox of my Sherpa, glued the cracks:

As you see very scratched, there where some deep scratches also on the sides,

get rid of them with groove sandpaper wet and dry (240):

Then do the sanding over and over again using finer grain:

The differences between 400, 600 and 1200 are not so good visible but you feel it,

here after the polishing, the photo is taken in side light so you can see the surface very well.

[nigel dabster]

there is a big difference in the type of plastic and finish required between a bultaco plastic tank (textred) and an airbox (smooth).

Anyone who puts wet and dry to a bulto tank would end up in a mess don't do it!

[toofasttim]

there is a big difference in the type of plastic and finish required between a bultaco plastic tank (textred) and an airbox (smooth).

Anyone who puts wet and dry to a bulto tank would end up in a mess don't do it!

I've wondered about that. The standard 199A tanks were textured but then you see the Puma bikes with painted tanks. Did Puma sand down the tanks and then paint them?

[pschrauber]

The gastank is a little bit grainy, but only a little bit, you can compare it to older bumpers when painting these where not in fashion like nowadays, (the main difference is the plastic, the bumpers are made out of harder plastic, (PP or PVC), the Bultaco gas tank material is very soft, I believe it's made out of PE-HD, like the airbox too, (PE-HD is oil and gasoline resistant)).

After some use the surface of the tank gets a little bit grey, this comes from cleaning the

tank with rugs an cleaning solvents and look like this, the greyish color comes from micro scratches

on the above located surface, the "lower" situated surface is still ok and so the blue is still visible.

As I mentioned already in my first post a photo of the tank would be nice to look up what is the best procedure to solve this problem, we don't have any so we have to guess.

Nevertheless the grained surface is very smooth, the "modulation" might be 200 - 400My, (0,2 - 0,4mm) as already stated with the fine sanding you can get the surface clean and when beginning with fine sandpaper the hopefully clean (*) lower surface will remain. If the tank more scratched or white then use a eccentric sander, beginning with 150 grain then 240 grain, you simply align the surface. then follow as mentioned befor.

Best way is to make some small test where you later not see your try out, like the surface under the seat.

If I have enough spatretime, whichever is rarely, I can show it.

I still have the old gastank of my bike laying around in the garage, (production year of the gastank is 1978! but was fitted to a 199b), the bottom filled with gas gum, plastic penetrated with premix, paint showing bubbles, ...), I can make a quick show and tell if someone is interested.

[woody]

I've wondered about that. The standard 199A tanks were textured but then you see the Puma bikes with painted tanks. Did Puma sand down the tanks and then paint them?

The tanks you see on the Spanish bikes are new fibreglass tanks, not plastic.

Still not convinced about this petrol vapour permeating plastic tanks theory. My SWM Jumbo tank has discoloured to a darker yellow over the years, I think from UV. If this was due to petrol vapour why is it only the exterior surfaces that come into contact with sunlight that have darkened. The underside is still bright yellow and if I take the side badges off it is still bright yellow under them too. So why doesn't the vapour affect the underside and behind the badges?

I have a plastic Sherpa tank that was painted properly by a car body painter about 4 years ago and it only has one or two recent bubbles, reason unknown although it is in the lacquer around a decal, but if petrol vapour was seeping through it would have lifted it all by now. A mate has a plastic Fantic 240 tank that was painted well over 10 years ago, not one imperfection in it. Neither have any lining inside.

If you have a really scuffed plastic tank, you may as well have a go at getting it painted properly (ie not by aerosol can) Most problems with painting plastic tanks may have come from incorrect or no preparation and use of incorrect paint type. Only my theory of course but if someone can explain why petrol vapours don't discolour parts of a tank that aren't exposed to UV, I'm willing to listen.

[toofasttim]

The tanks you see on the Spanish bikes are new fibreglass tanks, not plastic.

Thanks Woody

[cmc84]

Sod it, ordering a new red one. Red tank, black plastics and black frame...

[pschrauber]

The tanks you see on the Spanish bikes are new fibreglass tanks, not plastic.

Still not convinced about this petrol vapour permeating plastic tanks theory. My SWM Jumbo tank has discoloured to a darker yellow over the years, I think from UV. If this was due to petrol vapour why is it only the exterior surfaces that come into contact with sunlight that have darkened. The underside is still bright yellow and if I take the side badges off it is still bright yellow under them too. So why doesn't the vapour affect the underside and behind the badges?

I have a plastic Sherpa tank that was painted properly by a car body painter about 4 years ago and it only has one or two recent bubbles, reason unknown although it is in the lacquer around a decal, but if petrol vapour was seeping through it would have lifted it all by now. A mate has a plastic Fantic 240 tank that was painted well over 10 years ago, not one imperfection in it. Neither have any lining inside.

If you have a really scuffed plastic tank, you may as well have a go at getting it painted properly (ie not by aerosol can) Most problems with painting plastic tanks may have come from incorrect or no preparation and use of incorrect paint type. Only my theory of course but if someone can explain why petrol vapours don't discolour parts of a tank that aren't exposed to UV, I'm willing to listen.

My two cent experience:

Discoloring by gas vapors looks like this:

Difference in effect is that you find these brown / yellow coloring not only on the surface but also inside the plastic. When plastic is discolored by UV bright plastic parts like white light grey, ...turns yellow (darker) and dark plastic parts turns brighter, but only on the surface and through the whole material.

The next question is what kind of plastic is used and this question is really dificult to answer because it's mostly not recorded to the older plastic parts as nowaday. Even if you would no it's PE for example there exists at least 6 different PE plastics, only PE-HD for example is completly resistant against gas vapors the other PE plastics, like PE-LD, ... not.

The fibreglass gas tank are all reproductions and are not street legal. The plastik tanks where approved by Bultaco trough the German T