Gas tank leak at weld

On my KZ750E I have a very small, but highly annoying, gas tank leak. It is coming from underneath the mounting bracket that is spot welded onto the tank bottom at the rear. I cleaned the surrounding area down to bare metal, then tried using JB WELD, which worked for a few weeks, then started disintegrating. I then cleaned off all the old JB WELD, scuffed down to the bare metal, and used some special epoxy type putty made just for gas tanks (got that at the local Kragen Auto Parts). That lasted for about one week. Well, dammit, it started dripping again, once again messing up the repaint on my side cover.

I have been avoiding doing full coating on the interior of the tank, since I know the one spot the leak is coming from, and I have heard too many stories about people gumming up their entire fuel delivery system with badly done tank sealing.

Will it work if I get some tank sealer, and coat only the interior portion of the tank where the leak is located? I would use the POR product, since most people seem to think it is superior to Kreem. I could attach a small brush head to a wire coathanger, and paint the area from the inside through the top hole.

As another alternative, I was thinking about painting some gas resistant gasket cement (that purple stuff) onto the inside of the tank at the leak area.

What do the great KZrider Oracles have to say about the fix for this problem?

Any other ideas??
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have it welded/brased

What I know about KZ750s would fit in a shot glass, so I'm assuming that the leak is underneath the tank and out of normal view...

A picture of the area would be helpful...

Obviously, some type of stress is being applied to the tank at the bracket, which is I'm assuming is at least a partial cause in the first place - you didn't mention the condition of the interior of the tank.

Best way I'm aware of to fix one of those:

Empty the tank. Flush well with water. Leave the gas cap off.

Mask off the area immediately surrounding the bracket with duct tape. Sandblast, then wire wheel the area.

Surround the area with soaking wet rags.

Heat the area with a propane torch, solder the area around the bracket junction heavily - enough for the solder to pool.

Cut a "U" shaped patch from 16 gauge steel that fits around the bracket junction. Wire wheel it clean.

Get the pooled solder hot again, press the patch into the pool to fit around the base of the bracket. Apply solder as necessary to insure that the patch is both attached to the base of the bracket and the tank.

The purpose for the patch is not so much to stem the leak as to distrubute whatever load is being applied to it to a larger portion of the tank area.

Match and feather poaint to cover the area.

That'll fix you up.

lifeliberty wrote:

have it welded/brased

That's an option, but whomever's doing the torch work better be an artist - the temps are high enough to make big holes out of little ones...

Also, it doesn't address why the tank began leaking in the first place, which is stress on the joint...

Of the two, brazing is the better option because it's a lower temp operation and adheres well to clean steel.

I doubt that any type of internal sealer is a long term fix as any applied stress that was able to crack the tank metal would certainly be able to tear the sealer in short order.

The advantage of the solder idea is that done coreectly - no cold joints - it imparts a wee bit of flexibility to the area, as the lead in the solder will stretch before it breaks.

Post edited by: Pterosaur, at: 2006/06/27 16:22

The stress on the bracket probably came from the crash that caused the big dent on the side of the tank (not me, the PO). That has since been filled, and the tank painted. What I did not appreciate was that the crash may have caused the hold-down bracket to overstress, and ever so slightly crack the spot weld holding it onto the tank. This will not be a "forever" tank, so I just want to get it to stop dripping on my sidecover for six months or a year until I can find a better tank.

I have been looking for a better tank, but they are very few and far between for the KZ750E series bikes. That is why I bondoed and repainted this old tank -- it was that or put on a Harley tank that someone else made me take when I picked up my first KZ project bike from their backyard (no, I would not really do that).

Sorry I do not have a picture, but just imagine a piece of stamped metal, L-shaped, with one of the flat sides spot welded onto the tank bottom, and a bolt hole on the side sticking up through which a hold-down bolt passes..

I do not have any brazing or welding capability, plus the idea of using a propane torch around a gas tank scares the hell out of me, and will likely result in my wife sending me to the local 24 hour hold factily at the psych ward. I am truly hoping to find a cooler fix.
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apeman wrote:

... I do not have any brazing or welding capability, plus the idea of using a propane torch around a gas tank scares the hell out of me, and will likely result in my wife sending me to the local 24 hour hold factily at the psych ward. I am truly hoping to find a cooler fix.

Something I didn't think of the first time was to ask whether you had wire wheeled the spot in question to get the paint/gas/crud/whatever off the spot.

The best adhesives in the world won't stick to a cruddy, non-prepared surface. The material to be bonded has to be roughed up in order to give the bonding material something to stick to.

You could wire wheel the area, and give the JB/Epoxy route another try - I'd forego the putty for a two-part gel type like Kwik Set:

www.sigmfg.com/IndexText/SIGKS001.html

It's available at hobby shops.



In precise terms, clean the area well with a wire wheel and goop the livin' snot out of it. Give it at least 24 hours to set.

If that doesn't work, take the tank to a radiator shop. They've got the propane, they've got the skill, and they likely do much bigger jobs of the sort pretty often. You might get away for as little as $20 if you find the right old core-swapper...

Post edited by: Pterosaur, at: 2006/06/27 20:29