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Old 12-20-2007, 11:38 AM   #15
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1975 29' Ambassador
Littleton , Colorado
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Tank Repair

Here is a few pics of the plastic welding process. I went down to target and got the cheapest cutting board I could find. With the band-saw cut 1/4 x 1/2 strips and then halved the strip to get a 1/4 x 1/4 size. Used the Harbor freight welding gun at around 3.5 psi. I had to turn the compressor reg down and the gun reg to get down that low. I cut a V in the tank making sure to round out were the crack ended. I clamped the to pull the seam together and used a square end drimmel cutter. It doesn't have to look good. I went along the three edges tack welding(see pics). I left the rods sticking up and went back after it had cooled and cut them off. Finally I ran several beads down the crack until it was full. I worked on one side and then moved to another to allow for cooling. The whole process took no more than 45 minutes. Let me know if you have any questions.
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Master of the Tin-Can
and thats not saying much
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Old 12-20-2007, 02:48 PM   #16
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1977 31' Sovereign
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Most all plastic parts (including a cutting board) have an material recycle identifier on the bottom in or below the triangle. It will be a number from 1 to 7 and likely several letters. PE means Polyethylene, PP is polypropylene, PETE is thermoplastic polyester (soda pop bottles), PVC is polyvinylchloride.

Your weld looks pretty good. Sometimes you can preheat the tank with a haridryer type hot air gun they use for paint stripping to get the tank a little warm before you start to weld and it will releave some molding stress. You can also do it after the welding to aneal the weld and make it more ductile.

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Old 01-28-2008, 10:48 AM   #17
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Up front, let me just say I haven't done a water test, but the repair seems very sturdy. That being said...

I cut a final set of gussets and shims out of LDPE. You can see the outer diameter of the fitting inside the tank is much smaller that the diameter outside. The shims go under the flange to provide the proper angle between the tank skin and the fitting (or what I perceive as the proper angle). There's no way to tell unless I drop the tank. The gussets are 1/4" thick, so there is plenty of height, even with the shims in place, to get a good glue joint to the edge of the flange.

I did note yesterday that in taking the fresh tank out of the Safari, the top was not flat, but drooped. That may be the case here, which means the top skin would come back up "flat" once the tank is full. But that's water over the dam, as they day.

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The white in the lower left portion of the clamp photo is a stiff piece of paper on the face of the ceramic heater. I applied heat locally for about 3 hours. When I look at the photos, it makes me think "that inner gusset can be inserted from the top?" Yep. Just use several pairs of surgical gloves to keep the very Nasty smelling Scotch Weld off the skin. I think I had 25% of the glue on the gloves...

If this worked, the Sovereign is back in business!

BTW, if you decide on using Scotch Weld, get plenty of the 10:1 mixing nozzles. I bought six and with all the testing and self-doubt, I used 4 to get to this point. I wish I had bought 10. (If you're careful, you can re-cap the glue after using only a small amount from the dispenser, so the mixing nozzles seem to be the limiting factor in getting the most out of a $30 tube of glue.)

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Old 01-28-2008, 02:45 PM   #18
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I think Zep is past the point of no return... to close to the target and not enough fuel to make it back.
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Old 02-23-2008, 01:40 PM   #19
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oh, happy day

Finally got warm enough to hook up and go test the tank. If you recall, the problem in detecting the crack in the black tank is that I didn't overfill it, so any problem on the top skin would go undetected until you started sloshing down the highway.

So my test rig had to enable filling the tank above the top. Here's the solution--it appears than almost any hardware store will have the male PVC fitting that has the same threads as the toilet flange. With the toilet flange removed, just screw in the "test device" and fill to about 6" above the top of the tank. 6" inches of water is not a lot of pressure (about 0.25 psi)*, but that puts about 200 lbs of force on the top skin from the inside, which is enough to flex it a little and open any cracks.

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After five minutes, no detectable leaks! The Sovereign is practically ready to roll to Burning Man! Now we'll see if the glue can handle the stresses of the slosh over many miles...


* one atmosphere (14.7 psi absolute) equals about 34' of water, so if the test rig was filled exactly 6 inches, it would be more like 0.22 psi.

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