The gas cap has a fiber washer, so I assume gas is always evaporating out of the cap and getting under the paint. So of course the paint is starting to peel. Suggestions? Thank you.
What a tragedy! You put such a nice finish on the tank, and now...
The chances are the vapors are escaping from UNDER the fiber washer, which puts them under the paint film. The vapors are then exacerbating the natural difficulty of paint to stick to a galvanized surface.
Unfortunately the ruined paint will need to be removed and the area re-painted, but I would suggest that before you do that, you try to fix the problem.
Try an O-ring instead of the fiber washer.
And make sure the fumes have a way to escape, which is usually a small hole in the cap. The positioning of that hole should direct the vapors up and away from the paint film. I can't see such a hole in your picture, which doesn't mean it isn't there. That hole, by the way, also lets in air to replace the fuel as it's used. It's necessary.
I agree ... vent hole needed .. or unplugged, if there, but not clear.
Some of the gas caps have a splash guard crimped to the bottom to prevent fuel from splashing directly into vent hole in the top. The one on my ’26 doesn’t have the splash guard and some gas splashes out the vent hole when the tank is over 3/4 full.
(Message edited by AzBob on August 08, 2017)
Peter's suggestion of an O ring makes good sense. A fibre gasket will stop liquid passing but it is permeable and will allow 'wetness' to pass. You never see this as it evaporates as fast as it gets through. An O ring is impervious to liquids and should seal the cap.
The tank must be vented to air. A hole in the cap is the usual method. The baffled caps are best if the filler is adjacent to paintwork, helping to prevent fuel slop. A cumbersome but quaint fix is a coil of small diameter copper tubing soldered over the vent hole. I am almost at this stage with my roadster filler. My temporary fix is to run the car 3/4 full.
Hope this helps.
Allan from down under.
What type of paint have you used?
It appears that the paint has "wrinkled" meaning the gas has attacked the paint and reacted with it making it swell up.
If it was just gas getting under the paint surface between the metal and the paint the paint would just become loose lift and peel off.
Check out the gasket from an oil filter. They're flat and will compress better than an O ring maybe. I found some from a foreign car oil change dumpster that works perfect on my Torpedo cap.
Our gas doesn't bother the rubber on mine.
Oh Another idea that I use is to solder a copper tubing cap to the underside of the gas cap if gas is coming out of the vent hole. The space inside the cap traps the gas and allows it to flow back into the tank but keeps and air gap under the T cap.
Peter I think has the start of the answer--"what kind of paint did you use?"
It was painted by an auto repair shop. I do not know what kind of paint they used.
Not all paints are "ethanol proof".
Not all paints are solvent proof of any solvent, if the paint primer and top coat is not one with a hardener in it ( and its not mixed and applied properly) then the paint will eventually fail.
Modern vehicle factory finishes don't do this and if parts such as this tank or any tank especially a bike tank where the gas can come into contact with the paint don't have hardener induced primer and paint which will result in the paint chemically changing into a rock hard finish then it will fail.
If this failure is due to gas being able to penetrate through a crack or a small hole under the actual paint surface then nothing will prevent the paint lifting off.
First step to solve your problem would be to check with the body shop as to exact;y what they used for all the paints involved then we might be able to see the cause.
Ah, a common downfall of speedsters. Gasoline tanks that should be utilitarian and hidden under something, made to look pretty and in full view.
One simple "fix" that I have seen on several speedsters is to paint a contrasting circle around the filler (usually a little less than an inch wide line drawn around the outside of the filler). It could be in simply black, or matching whatever other contrasting colors or the numbers used. It also could be a color similar to the body color, just enough shades off to not catch the eye so easily, yet look like a contrast that belongs there.
It won't stop the problem. But it makes it easy to touch up often.