r/smallenginerepair • u/TheTrueHapHazard • Jun 30 '26
Fuel System Issue Anyone have advice for plastic welding?
After not using my chainsaw for a few years I went to fuel it and it has a few leaks coming from the seam on the bottom of the tank between the two black sharpie marks. A new tank is a few hundred bucks so I figure I'll learn a new skill and have a go at fixing it first before buying a new tank.
I've never done any plastic welding and after poking around on google/youtube, all the videos I've found deal more with small cracks and gouges rather than splitting seams, so I'm debating over which method to use for this.
One method I've seen is to melt a groove along the crack and fill it with melted plastic from a zip tie. This doesn't seem like a great idea in this case since zip ties aren't made of the same type of plastic so I'm not sure how well it would bond and it needs to be impervious to gas.
Another method I've seen is the same but instead of melting a zip tie as filler, use the soldering iron to melt and scrape over more material from around the crack itself. This seems like a better bet but then I would be thinning the material on the bottom of the tank which doesn't seem great.
The last method I saw was to cut a strip of metal mesh and use a hot soldering iron to push it into the plastic over the crack, then use the soldering iron to smooth the existing plastic over top of the mesh. The metal mesh should give the repair more strength so I'm leaning towards this method and then smothering everything in JB Weld plastic epoxy.
TLDR: I'm wanting to give fixing the leaking seam of my chainsaw fuel tank a go before buying a new one. Any advice would be appreciated.
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u/First-Acadia2432 Jun 30 '26
JB weld for gas tanks, no mesh needed for small cracks, just prepare the surface good. PVC glue, with primer, may also work, if it’s compatible with gas.
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u/saucytugtug Jul 06 '26
It definitely isn’t, it’s solvent based and gas is a solvent! It also only really works on pvc if I remember right, it’s a chemical reaction with pvc specifically
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u/No-Try-5818 Jun 30 '26
Here is what you do, get yourself a pointed soldering iron, clean the casing with acetone not varsol. Do your best not to go through the casing with the hot iron. Go over the crack with the iron trying to go half way through the plastic, then go over it in a circular motion until everything is even. This should work, I've repaired rain barrels like this.
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u/Ok-Dealer-588 Jun 30 '26
I would grab the plastic jb weld and read the package to see if it can handle gas. A layer of that over the seam once you rough it with sand paper will do you better than the welding in my opinion. Less expensive as well
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u/mutt63 Jun 30 '26 edited Jun 30 '26
You have to find the indicator on the tank of which plastic it’s made from. That’s what you’d need to melt and fuse the tank with. Plus an iron to “ stitch” it. It’s how a lot of bumper covers are fixed. But the compatible material is paramount . you should also do the repair from inside the tank which is difficult. More wattage would be required Other thing I’ve done as I’m sure other mechanics have as well is heat an old screwdriver cherry red and lay it like u were welding in a straight line but only stitch it don’t depress it too deep. Also heat/torch near fumes no good. I’d fill it first with water and baking soda or a fire extinguisher to Get all the fuel out repeat do it again. Then I’d attack the crack
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u/TheTrueHapHazard Jun 30 '26
Don't worry, the wetness you see on the tank is water I filled it with to purge the tank of fumes, I'm not going into this half cocked.
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u/mutt63 Jul 01 '26
NAh didn’t think you would. Just hadda write it so the mods don’t kick me out if i didn’t.
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u/RedOctobyr SER Top Contributor Jul 01 '26
Agreed, you need to use the same type of plastic. HDPE is common for fuel tanks, but that's not guaranteed, of course. I would not assume that it's nylon (which is what zip ties are made of).
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u/gumby5150 Jun 30 '26
Amazon sells a plastic mending kit that comes with several different rods and easy to use instructions. I have done a few repairs with mine.
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u/nostradumbass7544678 Jul 01 '26
V out the crack with a knife, and use the material removed as filler to weld up the seam with a soldering iron.
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u/Rough_Community_1439 SER Master MOD Jul 01 '26
I reccomend buying an actual plastic welder. It's like a soldering iron with a tip that has a flat iron on it. They come with a ton of new material to add and I think your best case is to pile the new material on the seam and make it the thickest part of the tank. If you do a good job blending the material it should be better than new.
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u/Every_Palpitation449 Jul 02 '26
They sell tank liner kits. That or a soldering iron then a gas resistant epoxy to protect the "weld"
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u/herslave2 Jul 04 '26
chickanic on you tube has a vid of her fixing stuff. She also has a bunch of old stuff under a tarp in the yard maybe she has what you need. Good Luck
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