Pressure in fuel tank

[motorplex88]

Acquired an 80 model wide glide late last summer and finally got around to taking it out on a shake down run. Riding with some buddies for about 70 miles and decided to stop in a place for a beer and a burger. Parked out in the direct sun and was in the joint for about an hour. Came out to find fuel all around the bike. I knew I shut the fuel off, so upon inspection found the left tank rear mounting tab with a hairline crack where it joins the tank. Was going to drain the left tank and just run off the right. Went to take the left fuel tank cap off and the thing had so much pressure in the tank it blew the cap out of my hand. Checked the vent it the right tank and seems fine. After the pressure was off,  the leak pretty much stop ed so I went ahead and rode it home with no issue I still have to fix my tab but I can't ever remember by gas tank building pressure. Any thoughts.

[JW113]

Mine gets pressurized as well, never to the point of blowing the cap off though. I think by design they're supposed to be that way. The valve in the right side tank lets air in, but does not let it out.

-JW

[motorplex88]

I suppose just sitting out in the hot sun on an 80 degree day made for excess pressure. I will pull the tank and repair. Hopefully I won't have to re-paint. I just thought it was unusual to have THAT MUCH pressure. The bike ran flawless otherwise. Makes my other shovel seem like a sissy !

[JW113]

I have found the pressure goes up as the fuel level goes down. How much gas was in the tank?

If you don't want to repaint the tank (rhetorical), then clean the paint from the cracked area and JB Weld it. And have the tank cleaned out and coated with Red Kote at a radiator shop.

-JW

[xlfan]

The  vent/equalizer tube under instrument panel is open in both ends?

[motorplex88]

The tank was about 1/2 full . To be truthfull I never thought about the top crossover vent tube. I will have to check that out. I think I can get away with just tig welding the small crack at the tab without a re-paint. When I got the bike, all of the existing tank liner had deteriorated badly and had to be cleaned out. Probably was leaking in the first place and previous owner did a poor job of lining the tank. Don't know for sure as the bike was in storeage for a long time.

[david lee]

make sure theres no petrol fumes in tank before welding.you dont want a big kaboom

[JW113]

If the crossover vent tube is not connected, there will be no pressure as that line is to allow air from the right tank into the left tank. No line, it all vents to the air. Not good in a closed garage with water heater or gas dryer.

If you can weld it, even better. I think when they weld gas tanks, they keep a purge line of nitrogen or helium flowing into the tank.

-JW

[Coff 06]

Dry ice also works great to neutralize the tank for welding.Usually easy to find.        Coff 06

[Hossamania]

If the crossover vent tube is not connected, there will be no pressure as that line is to allow air from the right tank into the left tank. No line, it all vents to the air. Not good in a closed garage with water heater or gas dryer.

-JW

Not good in any garage.

[motorplex88]

Welding gas tanks is a everyday occurrence to me.  Drain, steam clean, and purge with inert gas while welding.  I'll pull it apart, give it a fix and ride her some more. I'll report the results. Oh, I also need to true the front spoke wheel.

[Racepres]

Welding Fuel tanks is Not something I undertake... leave that to Professionals...
the Product Known as Seal All


works miracles, and lasted about 5 years on the Side mount of a Shovelhead here..

[a_disalvo]

Permatex makes an epoxy just for fuel tanks, I have used it with excellent results. Frank

[PoorUB]

One more vote for Seal All. I have used it many times to seal leaking fuel tanks.
I worked at a real service station in high school.  That is where I first used it. I would have someone bring in a car with a tiny pin hole in the tank. I would tank emery cloth and clean the area of the hole down to clean metal. They usually dripped fasted then. I would put a glob of Seal All on one finger and the air hose in the other hand. Blow the hole off to dry it off and jam the finger of goo over the hole. It might have taken 2-3 tries but I could get it to stop. Then 2-3 more coats of Seal All and no more leaks.

[motorplex88]

After I get the tank off and onto the bench I'll see how bad it is. I might try the sealant route but I've been welding professionally for 40 years so that's just the way I normally go.....but I'm always willing to try a product that I have never used before especially if others have had good luck with it. I probably won't get to it till the end of the week because any more by the time I get off work, all I want is my recliner.

[david lee]

cant see that stuff working on a mounting point.but worth a try i spose

[Hossamania]

If I were able to safely and competently weld it, that would be my first choice.

[PoorUB]

Yes, if it is cracked at a mount, I would weld it.

[motorplex88]

 I'm not the first guy to be working on this.

[motorplex88]

Out of the blaster and on to steam. I should have taken a picture of the wad of epoxy that was there.

[JW113]

Hey I'm always up for information exchange. So what is your method?

-JW

[david lee]

definitley a weld job from memory that mounting point has a spacer and if not installed theres to much pressure when the bolt is tightened

[motorplex88]

Don't laugh 😂. Man this thing is turning out to be a bitch. I'm guessing the tank liner is messing with me cause crap keeps blowing out of the weld. I was surprised that the steam clean didn't take  all of the liner out but some remained. It's holding pressure finally. To be honest I would not know if this is a knockoff tank or not. I know it's damned thin. The spacer was present upon disassembly and nothing seems in a bind.. obviously someone has been working on it before so who knows what really happened before hand.  JW. On this particular one , I dug all the epoxy off, sandblasted, ground all the previous welds off and steam cleaned the inside. There was not even a whiff of gas fumes left so I went to welding. If I detect any fumes at all I will purge the tank with whatever inert gas I have available (argon, nitrogen, helium ect.). I now no why the previous repair was finished with epoxy. They got tired of pin holes blowing out 

[david lee]

it might need reinforcing around the mounting point. if the metal is thin it will more than likely keep cracking

[JW113]

If it didn't go Ka-BANG at the first application of the heat, I think you're probably OK. If it were mine, I would still have it lined with Red Kote and not worry thereafter. Who knows how many more rusty thin spots are lurking inside.

Good luck with it,
-JW