Plastic Tank Repair!

[viclioce]

HELP!!! Can anyone tell me a good glue or repairing substance to use for repairing a plastic fuel tank? I have a plastic tank and there are 4 brass square shaped nuts which have fuel tank molded around them. One of them broke loose and started spinning in the plastic recess for it. This wore through the plastic tank and needs to be repaired. I have modified the opening to hold a steel acorn nut in place of the original. I thought JB Weld would hold the nut in place and fill in the gaps where the plastic cracked.

NOT SO! It leaks worse now than before I started working on it. I need something which will both seal the cracks and will be fuel proof. I have just been told that JB Weld does not stick well to plastic and is also fuel sensitive! Any suggestions will be appreciated. This KTM 50 I have is for my younger grandsons. But I can't put fuel in it without it leaking out, badly! And I am at a loss to find a replacement tank for it. It's a 1996 model KTM 50SX, and I believe an SX Jr. KTM doesn't even list the bike or parts for it any longer. They list the newer ones, but the tanks mount differently and I don't know if I can mount a newer tank on this older frame because the newer tanks do not have the front mounting tab this one has which gets bolted down to the frame tube. So I have to throw this thing away if I can't repair or replace this fuel tank! Just trying to keep another old bike running!

Thanks in advance for any advice you folks might have. ; D Victor

[BrianZ]

There are people who specialize in plastic welding. I have a friend who has an 80's YZ125 that uses a "one model year only" plastic tank. He has had it plastic welded several times to repair cracks. The system uses heat to melt the plastic, and plastic filler rod to build up the repaired area, much like metal welding. The repair technique is very popular with modern road bikes, as replacement fairing parts are expensive. Now you need to find someone in your area who has the equipment.

Brian

[Zyx]

You can weld it yourself with a soldering iron and plastic filler. I have used zip ties as filler. Glue won't work.

[Bullfrog]

And you are going to have to remove ALL of the glue to do the welding repair. Seems like using pieces from another plastic tank - or plastic fuel can - would be a better material match than zip ties?

Ed

[Zyx]

Probably. If you can identify what type of plastic is used, such as HDPE, you can use anything made of the same stuff from milk jugs to oil cans.

[Bullfrog]

Oh, good thought Arizona -- plastic quart oil containers (well washed, reallllly well washed) ought to be good filler material for patching a plastic tank.

Ed

[RichardMott]

A couple of years ago at Hodaka Days, Chuck Swanson demonstrated the art of plastic welding. I think he might have gotten the kit from Harbor Freight.

[Zyx]

Most product containers these days are marked as to their material for recycle purposes. Gas tanks, not so much. If in doubt, you can always contact the manufacturer and ask, but I am going to guess they are either high density poly or low density poly, and I would lean toward high density, or HDPE.

Of course, whether made of high molecular or low molecular density, polyethylene is still polyethylene. Since you will be using it as a weld filler, it's structure is likely to change anyway. Not being a chemist, I am not sure. Not being able to pass chemistry is why I dropped out of the pre-Med program in the last century. But I have repaired plastics with a soldering gun and now and then a micro torch. You just have to be careful.

And, since this is a gas tank, I would wash it out with detergent and water just to be safe, before applying heat.

Sounds like the area to be repaired is a stress point which makes it harder to do a successful repair. I would have to see it, but you may be able to either build up an extra thickness of material, like a goober weld, or imbed something for strength, such as fine wire or glass fiber.

When that doesn't work, you can look for a plastic welding kit at Harbor Freight.

And when that doesn't work, there are new tanks out there....

[viclioce]

Not being able to find a new tank is the reason I'm resorting to repair. When you say use a soldering iron, do you just heat the plastic being added or do you have to heat the plastic being repaired as well? ; D Victor

[Zyx]

Both, the idea is to create a more or less molten puddle in the area to be mended. If both are not approaching a fluid state, they will not blend and bond. You can use a micro torch, but it takes care not to burn through or ignite the plastic. A soldering gun is easier to control, but works slower, and you have to keep it moving.

Get a couple of old oil jugs or a plastic pail and see if you can stick two pieces together. Work on something similar but not irreplaceable until you have a sense of how to proceed.

[Zyx]

I have heard that Vic was able to repair his KTM tank with a JB Weld product. Since normal JB is simply epoxy and doesn't stick to plastic, I think we need a report on what was used and how it worked out. I was unaware there was anything at all that would stick to a plastic tank.

How about a report from NM.

[viclioce]

The regular JB Weld did not work! I was, however, successful with the JB Weld Waterweld putty. Is a two part putty that is water and fuel proof! I was able to mix it together by folding and squishing it. Then I pushed it through the hole until it penetrated the inside of the plastic tank. I was also able to embed an acorn nut into the putty and let it dry for a few days because I went out of town. When I got back, I was able to sand the dried putty smooth and flush with the tank outer skin. Put some fuel mix in the tank and it held! In fact she's sitting in the garage with fuel in it now which has been in it for two weeks and no more leaks! The WaterWeld putty works!!! ; D Victor

[viclioce]

I'm attaching a photo of the product I used to fill up the hole we had in the KTM 50 SXR's plastic fuel tank!

It's about $7-8 from what I remember. It's a 2 part putty, one part wrapped around the second part. All you do is cut off the amount you think you need and knead the piece to mix the two parts. It sets up quickly getting reasonably hard in 5-10 minutes so you have to work quickly once you knead it. Once dry, you can sand it if needed to make the exterior flush with the side of the tank! It dried nearly white for me. About the same color as the aged white plastic tank! Here's the photo! ; D Victor

[Zyx]

Thanks for the report, Vic. Sounds like a much better solution than trying to hot weld old plastic.

[viclioce]

Yes it sure was! And I didn't have to buy any new equipment or practice with it to be successful! I was surprised indeed that this one held and worked. I think pushing it through the cracks from the outside to the inside and letting it expand beyond the cracks inside made it hold much stronger. I don't know what the putty is made of, but it worked very well and has stopped the leaks! ; D Victor

[Zyx]

Does the bonding material remain flexible once cured or become rigid? You mentioned that it was sandable, but I am curious about its ability to withstand vibration and flexure over time.

[viclioce]

It seemed to dry to a similar consistency of dried Bondo. I would not call it flexible. ; D Victor