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Author Topic: Gas Tank Blistering  (Read 8148 times)

Offline Kchop

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Gas Tank Blistering
« on: May 16, 2025, 11:30:38 AM »
Hey Group,

Just started riding for the season and noticed paint “ bubble-up” on bottom of gas tank. Rubbed my thumb over it and definitely soft and smells like gas. Is it possible that mixture of gas and stabil is “eating” through the gas tank?? Maybe rust inside the gas tank?

Anyone have any experience with this??


93 K75S

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Offline Laitch

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Re: Gas Tank Blistering
« Reply #1 on: May 16, 2025, 12:09:49 PM »
Your Brick's tank has pinholes caused by corrosion. They will need to be closed by welding or chemical coating of some kind.

The addition of Stabil to fuel doesn't cause rust. Tank corrosion is caused by the interaction of the elements in water that has separated from old fuel. Stabil is designed to inhibit such precipitation but its effect in fuel lessens as treated fuel ages past one year in the tank; Stabil has no ability to reduce corrosion that has already started previous to its use.

There have been many discussions on this site about successful treatment.
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Offline frankenduck

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Re: Gas Tank Blistering
« Reply #2 on: May 16, 2025, 12:12:04 PM »
The tank is an aluminum alloy. It can't rust (only iron can rust) but it can corrode. Yes, the paint bubbles and gas smell indicate that the tank is leaking.

It's caused by ethanol laced gas absorbing water from the atmosphere (humidity) and the water causes the tank welds to corrode. Not uncommon for K bikes that sit for extended periods.

Stabil helps keep ethanol gas from absorbing water and helps prevent that from happening.

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Offline Kchop

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Re: Gas Tank Blistering
« Reply #3 on: May 16, 2025, 12:28:29 PM »
Arghhhh....! Just want to ride one season with no drama..anyway

Thank you guys for the reply,

Can you post a link for repair and mitigation, if you know where one exists. I saw in here somewhere a guide to tank removal as well I think.

Appreciate the help.
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Offline Laitch

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Re: Gas Tank Blistering
« Reply #4 on: May 16, 2025, 01:50:33 PM »
You think this is drama? Think about doing this repair in Kyiv.

Here's some advice from The Mighty Gryphon, a member experienced in many forms of Brick repair artistry, and others who confirm its efficacy. blackie1 seems satisfied with the results.
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  • Along the Ridley in Vermont.
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Offline Kchop

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Re: Gas Tank Blistering
« Reply #5 on: May 16, 2025, 03:12:08 PM »
point taken....
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Offline Chaos

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Re: Gas Tank Blistering
« Reply #6 on: May 16, 2025, 09:50:46 PM »
If it makes you feel any better, usually they corrode at the bottom front corner, yours' is an oddball.
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Offline Kchop

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Re: Gas Tank Blistering
« Reply #7 on: May 17, 2025, 11:08:42 AM »
yeah, nothing over here makes sense.....
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Offline FTR

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Re: Gas Tank Blistering
« Reply #8 on: May 17, 2025, 04:13:45 PM »
Check your filler cap. My tank is corroding and leaking to the lower shoulder both sides. When I drained the tank there was quite a bot of water in there which had been dripping I through the filler cap.
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Offline Laitch

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Re: Gas Tank Blistering
« Reply #9 on: May 17, 2025, 10:38:32 PM »
If you have the OEM fuel tank cap, is its hinge placed forward or rearward on the tank?
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Offline Duckbubbles

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Re: Gas Tank Blistering
« Reply #10 on: May 18, 2025, 09:12:59 AM »
Hinge to the rear.  It allows the drain hole in the cap to line up with the hole in the tank.

Frank
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Offline Laitch

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Re: Gas Tank Blistering
« Reply #11 on: May 18, 2025, 09:25:14 AM »
Quote from: Duckbubbles on May 18, 2025, 09:12:59 AM
Hinge to the rear.
Frank
You get an A, Frank.  :laughing4-giggles: If we can get Kchop's answer, that could help clarify the source of his problem. The link to The Mighty Griffon's work probably contains the solution.
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Offline Kchop

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Re: Gas Tank Blistering
« Reply #12 on: May 18, 2025, 09:54:20 AM »
Quote from: Laitch on May 17, 2025, 10:38:32 PM
If you have the OEM fuel tank cap, is its hinge placed forward or rearward on the tank?

Hey,

It's hinged towards the rear of bike.
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Offline Laitch

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Re: Gas Tank Blistering
« Reply #13 on: May 18, 2025, 03:29:06 PM »
The rim of the tank is designed to evacuate water by means of a hole along the rim's perimeter that connects to a metal pipe that passes through the tank's interior and out its floor. The stub pipe through the floor is connected to a hose that passes behind the right peg plate to dump water on the pavement. If the hinge of the cap is on the rearward side, the cap is in the correct position to allow this system to function.

Your cap could need a new gasket. The pipe should be checked for clogging and also for leaks into the tank along its length inside the tank.

Water released during fuel separation and/or water condensation within the tank from long-term storage are also common causes for water in the tank
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Offline Kchop

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Re: Gas Tank Blistering
« Reply #14 on: May 18, 2025, 07:52:14 PM »
Thanks for that explanation. Guessing I'll find the schematic to the pipe/peg plate, etc in the Clymer manual??

Adds a new wrinkle, guess its time to learn something new anyway
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Offline Laitch

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Re: Gas Tank Blistering
« Reply #15 on: May 18, 2025, 10:26:17 PM »
Clymer won't have a diagram, neither will Haynes nor BMW's K75 K100 2V manual downloadable from Motobrick. There are a couple of diagrams on the Web and this is one that seems suitable for the age of your Brick. You should be able to take it from here.
 :rideaway 
 
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Offline Kchop

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Re: Gas Tank Blistering
« Reply #16 on: May 19, 2025, 09:29:58 AM »
Thanks so much!! Time for investigation this weekend.....
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