Plastic welding a small fuel tank......

brino said:
I really do not know.

It is a Troybilt Horse model roto tiller (about 20 years old) with the wrap-around bush bar, so the tank is pretty well protected.
It was sitting in the sun for a couple hours just before I went to put it away.

My only other thought was that the pull-start handle hit the tank when I let go of the pull rope.
It does have a strong recoil.
But the pull-rope is way around front and this crack was at the back outside corner.

I do still wonder about a manufacturing defect as it was right where that flange meets the tank.
But still I guess I cannot complain, it has had a great run!

-brino

I do NOT have pictures of mine, but it is similar to the below:
(but my pull cord is on the same side as the fuel tank.....)

View attachment 324133

View attachment 324134
Click to expand...
I'm sure John has a lot of stories about tank failures both plastic and metal. Probably they could have gotten around that if the tank was not attached to the engine but to the frame. There is just too much vibration with a single piston engine. I had to braze up the gas tank and air filter on the cheapo rototiller I enherited. They put bigger tanks on them than law mowers.
 
Thanks for posting your adventure with plastic welding Brino. My favorite welding process has always been OA. Briefly got into OA welding aluminum and hope to get back to it. My FIL got approached by a company back in the '80's when everybody converted from wood field bins for stone fruit and citrus to plastic bins to repair them by welding. He was not interested because he could barely see to weld much less do something plastic. He also couldn't OA weld. I was intreagued but never saw the people again but was always interested in it. I'll have to look into the links you posted when I have time. I'm sure it's a really involved thing since there are so many different kinds of plastic. Still blown away that the best filler is coax insulation, whodathunk?
 
I've welded quite a few whitewater kayaks that met an early demise on some submerged rocks. Done similar steps to what you did. The biggest thing for us was to get full strength back since the hull is impacted often. I've never done steel mesh, but the club bought a hot staple gun that electrically heated "staples" (more like the lightning bolt shape from Harry Potter's forehead and no spikes on them) and pressed them into the hull. You'd do one of these every quarter inch or so, spanning across the crack. Finally you'd finish the weld with a heat gun, soldering iron, and filler material like you did.

1589381862776.png


Funniest one to date was my buddy bought a new boat that had a defect and the manufacturer would ship him a replacement boat for free (under warranty) only if he drilled thirty 1/2" holes into the bottom of the broken boat. He did of course and after the new boat came in, we painstakingly repaired every one of those holes and used the boat to teach our beginners. It never leaked but probably weighs a couple of extra pounds for all the plastic that was added.
 
Cool repair, and you added more knowledge to the ol' memory bank than what I had when I got out of bed this morning.
Now if I can just remember this if the need arises.

Did you do anything to the mounting to prevent it cracking again in the future?
 
middle.road said:
Did you do anything to the mounting to prevent it cracking again in the future?
Click to expand...

Honestly, the tank is still waiting to be re-installed.
Work has been getting in the way of play-time, so it likely won't happen 'til the weekend.

Plus I am not sure what I could do to help the situation....suggestions are welcome.

There is engine vibration; maybe add some rubber isolation between the tank and the engine?

Maybe I could spin the plate that mounts the pull-cord so that it comes out the "passenger side".

Without really knowing the root-cause, it's a bit of shooting in the dark.

-brino
 
brino said:
Honestly, the tank is still waiting to be re-installed.
Work has been getting in the way of play-time, so it likely won't happen 'til the weekend.

Plus I am not sure what I could do to help the situation....suggestions are welcome.

There is engine vibration; maybe add some rubber isolation between the tank and the engine?

Maybe I could spin the plate that mounts the pull-cord so that it comes out the "passenger side".

Without really knowing the root-cause, it's a bit of shooting in the dark.

-brino
Click to expand...
We'll have to see some picts when you get back on it to see how it mounts.
 
A few years ago when I was still building race motors I could have sent you a whole mess of those tanks. Hope your repair holds up but don't get mad with yourself if it fails again. It probably cracked from years of vibration and/or the fasteners holding it being overtorqued. I wouldn't try to re-engineer the mountings, if it still leaks check with your local small engine repair shop, they might have a tank in their junk pile.

If you want the pull start going the other way just take the bolts out and rotate it, that's how they work.

John
 
I traveled around the US inspecting HDPE tanks and having them repaired. The techs used a high wattage light and reflector with powdered resin and had very good control of the heat process. Move it around in a circle an vary the proximity to the tank wall
 
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