Mark 3 - gas tank leak - suggestions?

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Sep 26, 2007
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I was taking my tank (steel stock tank on a Mark 3) off today and gas started leaking onto my fingers as I loosened the right front nut.

My first reaction was, of course, denial: "this liquid on my fingers can't be fuel, my tank is perfect" Then the truth hit after I had the tank on a bench. It is leaking really badly from around the stud area.

I can even wiggle the stud a bit and see a paint bubble beside it.


Rode the bike over 200 miles yesterday and everything was working so nicely!!

I had an accident with the bike about 3 months ago, and the stud must have been stressed at its junction to the tank during the accident. Vibration since then must have finally resulted in a crack around the stud, and when I took off the tension today by loosening up the nut, it started to flow.

One option might be to just put the tank back on, tighten up the nut on the stud, and hope the tension holds the fuel in (just kidding! - I know what a gas fire on a bike feels like - been there, done that!)

anybody have any suggestions (other than buying a new tank). Some kind of goop/compound / a small weld around the stud,,, etc?

help - the weather is gorgeous and I wanna ride!!!

Keith Kelly
Encinitas, CA
Cut out the threaded bung and save it, fit a thick un-plated steel washer to the bung and gas weld it on the washer and than the bung combo back on to the tank. Don't braze it, don't silver solder it, don't MIG weld it,don't TIG weld it. No glue will hold this must be done old school. Find a small hand torch with an old man attached. 30 min repair after the first fifty or so. Good luck they are dropping like flies.
Norbsa -

thanks for the quick reply. Much appreciated.

However, I don't follow some of your terminology -

"cut out the threaded bung" I assume a "bung" is the stud? And cut it out how?

"Gas weld" a steel washer to the bung. I assume "gas weld" is referring to old fashioned welding with a torch?


Right on the gas weld and a bung is what that stud is screwed into. Female thread with a small lip were it meets the tank. This is a gotta do on all Interstate tanks because of the weight of the fuel.
Obviously working on a used gas tank with a torch is not for the beginner. If you don't know someone locally that you can trust, I will once again recommend Ross Thompson. It will require shipping the tank to Canada and back, but there is no question the work will be top notch.

When I sent my Interstate tank to Ross after some pretty ugly crash damage, he replaced a mounting bung that a DPO had screwed up and did some repair on the other one as it "looked like it was ready to leak".
There is no shortage of welders in my area, with several old motorcycle shops, chopper shops, etc.

However, my tank has an immaculate paint job, which I can probably kiss goodbye as soon as a torch fires up on the bottom right hand corner to weld the bung/stud back in. It will be $50 or less for the welding job, and $300 or more for repainting. Damn.

Of course, I will plead with the welder to work carefully and spare the paint, but I'm not hopeful.

By the way Ron, where is Ross Thompson. I travel back and forth to Canada pretty frequently, and depending on where he is, I might consider taking the tank along with me.


I have known fuel to leak down the stud / tank boss thread. The fix was to braze the stud into the tank boss. If this is the case with your tank perhaps modern glues etc such as Loctite might do the trick thus saving the paint work. If the tank is indeed cracked you're stuck with welding.

Best of luck,
The paint job is probably toast, and I would not trust glues. If it doesn't work and results in a fire that destroys the bike, you would lose a lot more than a paint job. Lining the repaired tank might be a good option too. Just in case the welder leaves a teeny little pinhole.

Ross is in Ailsa Craig, Ontaro. That's pretty far from your neck of the woods. Although no farther than your local post office. And no that is NOT my Interstate tank on his website. Mine was not that rusty. However, it probably was more severely dented. He has before and after pictures that he was thinking about replacing the ones on the website with.
And make sure you've got the correct type and quantity of tank front rubber mounting washers, rear rubber mounts, and strap, and the correct thickness foam rubber pads, so whatever the tank type and year model, it will be supported properly, and so puts less stress on the front tank mountings.

And Roadster tanks are not immune to the problem either, if they are not supported correctly?

Use this as a guide, but owners do need to check their own parts books for quantities etc.: ... &Plate=030
I've got a guy here locally, two actually that I would trust with my most treasured items. I would call each, two of the few remaining true craftsmen left. Just to qualify him a bit, one of my friends, Mickey Peters, repaired a Rocket Gold Star case that had a rod thrown through it. If I didnt see it, I would not have believed it. He put the factory texture back on the cases after he repaired the giant hole. You couldnt tell there was ever any damage. Absolutely seamless in every regard. His specialty is British bikes. My other friend, a bloke from Australia named Dingo (aptly named) does equally incredible body work. He is incredibly cheap, too. Not sure how he does it. Bakersfield is not far from your area. Worth the trip or the postage. 100% satisfaction. You can see the rechromed mufflers you sold me way back when. Cheers.
Appreciate all the info guys.

I took the tank to Don Angel, of Sonny Angel Motorcycles in San Diego. He took a look at it and said forget about using any kind of goop, or any welding technique other than a torch.

So Norbsa, he passed your test. He said the same thing you did. And he's done a few of these before. Says he thinks he can do it without damaging the paint on the tank itself, but I am a skeptic on that one.

PS - by the time I got the tank to the shop, it was leaking from both studs, and not just dribbling - it was really flowing.

LAB - good point on the rubber mounting washers. The prev owner had replaced them on the front with steel washers and I neglected to put rubber washers on. So when I had my accident (resulting in bent frame, bent forks, etc.) the front tank studs were solidly attached to the frame and took quite a hit. It took 3 months from the delayed consequence to come out though. Oh well, at least it didn't start pouring gas onto my hot engine a day earlier - as I was cruising at 80 mph on the freeway on a very hot day!!
4 years ago when my final drive chain snapped on my cb750, it left a hairline crack which leaked badly.I cleaned it throughly with acetone and a wire brush, smeared it with jb weld, that was over 50,000 miles its still sealing. I know norton are a different animal, but who knows?
You will never see me use the studs just for the crash reason. The exhaust ISO rubbers with the fine thread stud out each end work nicely for this. Add the stock rubbers as needed.
As one of the forum members once very strongly pointed out to me...not on a fiberglass tank! ISO rubbers don't work what with the cast in bolts.

Gosh...he'd be so proud of me for remembering that. He might even come back into the forum again and forgive my ignorance... :roll:
It's a miracle!

Picked up my tank from Sonny Angel Motorcycles on Saturday morning. Don Angel had told me he thought he could do the welds around the stud bungs without damaging the paint.

And I was a skeptic.

Mission accomplished! Tank has been pressure tested and filled with gas. No more leaks, and the paint job wasn't touched.

Guess he had the right touch with the torch, after all. Imagine me, doubting someone who has been working on Nortons (and Guzzis, Ducatis, etc.) for more than 40 years.

Now we'll see if he can ride a streamliner at 351 MPH at Bonneville over the next couple of days.

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