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Old 10-02-2019, 05:48 PM   #1
99sport
 
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Default Sealing vintage motorcycle gas tank leak?

Short version: I have a leak in my gas tank, It appears that it is NOT leaking at the soldered seam along the bottom of the tank, but is leaking from under the attached (spot welded?) mounting tab. I do not see any cracks / damage to the tank on the inside with an inspection camera. Iím not sure how to fix this as I canít identify the source of the leak. I am considering:
Kreem tank liner: https://www.revzilla.com/product/kreem-fuel-tank-liner
Any suggestions?

Long version: I have a 1972 Kawasaki 2 stroke motorcycle that I recently moved from California to Illinois. I left the bike with the gas tank full and added Stabil in early June. When I returned to Illinois yesterday, I found the tank sealer / liner that I put in the gas tank 20+ years ago had separated. (I don't remember what I used.) After removing the failed liner, I soaked the tank in Evaporust for a couple of days and found that it was leaking at the back. It seems the tank has been leaking from that area for a long time as the paint is gone there, but it was such a slow leak that I never noticed. (That area was coverd in black grime before I cleaned it and it is hidden under the seat.) It is now leaking fast enough that I cannot use the tank. The rust is removed from the tank and I need to fix the leak so I can use the bike.

Pictures of the inside and outside of the leaking area are below (note that there appears to be a seam on the inside of the tank along the tank centerline that is not visible on the outside). You can just make out the outline of the bottom of the mounting tab on the inside of the tank. (By the way, the dates on the inspection cam pictures are wrong.)

Any suggestions on how to repair this leak?
Attached Images
File Type: jpg Tank Leak.jpg (56.3 KB, 36 views)
File Type: jpg TankOutside.jpg (99.7 KB, 36 views)
File Type: jpg TankInside-1.jpg (39.7 KB, 36 views)
File Type: jpg TankInside-2.jpg (38.8 KB, 36 views)
File Type: jpg TankInside-3.jpg (41.6 KB, 37 views)
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Old 10-02-2019, 05:50 PM   #2
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Default Re: Sealing vintage motorcycle gas tank leak?

A couple more pictures:
Attached Images
File Type: jpg FailedTankLiner.jpg (85.8 KB, 36 views)
File Type: jpg 1972KawasakiG5.jpg (134.9 KB, 35 views)
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Old 10-02-2019, 05:53 PM   #3
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Default Re: Sealing vintage motorcycle gas tank leak?

Properly cleaned, Kreem would probably do it if not at a stress point. Since yours seemed to be under stress I would think it needs to be brazed. Have an expert do it. You don't want it to explode on you.

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Old 10-02-2019, 10:49 PM   #4
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Default Re: Sealing vintage motorcycle gas tank leak?

My uncle used to solder gas tanks with a large torch heated soldering iron. No flame involved.



If I were to braze, I would rinse it out with water, put my torch to the tank opening to burn off any fumes, then start brazing away.
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Old 10-03-2019, 12:33 AM   #5
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Default Re: Sealing vintage motorcycle gas tank leak?

Quote:
Originally Posted by flman View Post
...
If I were to braze, I would rinse it out with water, put my torch to the tank opening to burn off any fumes, then start brazing away.
Um... maybe rinse with some dishwasher soap and water many times?

Back in my younger days I used water to triple rinse a type 1 VW fuel tank before brazing. Triple rinsing is a laboratory standard after all. I was young, but smart enough to think, "Maybe there's some residual fumes left in that tank?". I directed my torch to the tank fuel fill neck. There was a very loud noise as the tank took off like a rocket. It was a learning experience. That was my one and only fuel tank brazing experience. I will add that it was successful.

Since that experience I've noticed that one method some professionals use is to flood the vessel with inert gas before applying the torch.

Carry on.

vic
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Old 10-03-2019, 02:46 AM   #6
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Default Re: Sealing vintage motorcycle gas tank leak?

Somewhere, I've got pictures of an old G5 I used to have for a while...

Similar to Kreem, I think POR15 makes a motorcycle tank liner product. I think I remember some people telling me that it was much better than Kreem.
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Old 10-03-2019, 04:18 AM   #7
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Default Re: Sealing vintage motorcycle gas tank leak?

Quote:
Originally Posted by Aqua Puttana View Post
Um... maybe rinse with some dishwasher soap and water many times?

Back in my younger days I used water to triple rinse a type 1 VW fuel tank before brazing. Triple rinsing is a laboratory standard after all. I was young, but smart enough to think, "Maybe there's some residual fumes left in that tank?". I directed my torch to the tank fuel fill neck. There was a very loud noise as the tank took off like a rocket. It was a learning experience. That was my one and only fuel tank brazing experience. I will add that it was successful.

Since that experience I've noticed that one method some professionals use is to flood the vessel with inert gas before applying the torch.

Carry on.

vic
That's my old dad's'wartime method with a fag (a woodbine--coffin nails) hanging out the corner of his mouth !
Flood it with nitrogen or fill it with water.
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Old 10-03-2019, 05:03 AM   #8
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Default Re: Sealing vintage motorcycle gas tank leak?

Water conducts heat - a problem. Nitrogen purge is normal for brazing. It prevents oxidation of the metal as well. The paint and whatever that inner gray coating is will all vaporize, though, such that you’d want to repaint the area, which might not be in the budget.
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Old 10-03-2019, 11:15 PM   #9
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Default Re: Sealing vintage motorcycle gas tank leak?

I have gotten some excellent advice here. I think that HighPockets is probably right that the strain at the mounting tab will likely jeopardize a tank lining repair, however I am going to try Kreeme anyway.

My rationalle is:
-I dont want to attempt the repair myself - I have reworked soldered copper fittings when I didn't want to replace them, and while it usually goes well, once in a while the repair takes too long and the joining parts get too hot and all the solder runs out and everything falls apart. If the solder / braze flowed out of the seam in my 50 year old tank I would have a real problem as new parts are hard to get.
- I am out in the middle of nowhere and I don't know where to take it - it took me 4 years to get someone to show up to trim my trees.
- I'm not sure where the actual leak is. It is leaking from under the tab that appears to be spot welded on, so the tab would probably have to come off to make a successful repair.
- It has the original paint on it and I want to keep it (and the "patina")
- It is only ridden a couple of times a year, and the slow leak, while unfortunate, isn't so much to prevent me from riding it - it is however a problem for storage.

So I am going to try Kreem. I looked at the POR 15 product, but Kreem was cheaper and seems to have good reviews. I do plan to leave the rubber band off that hooks over the mounting tab so the tab is no longer under strain. Even if it still leaks slightly, with the liner I can store the tank empty, or below the level of the leak, and not worry about rust forming. My girlfriend rides the bike around the yard once in a while, and a few minutes of leaking a couple of times a year won't be the end of the world. After all, it looks like it has been leaking unnoticed for quite a while. Finally, if Kreem doesn't work, I can always do a more permanent repair at a later time.

Thank again for all the great responses
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Old 10-03-2019, 11:19 PM   #10
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Default Re: Sealing vintage motorcycle gas tank leak?

Taking a closer look at the pictures, it appears the spot weld may have torn / cracked? See circle in picture
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File Type: jpg TankInside-1.jpg (37.4 KB, 23 views)
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