Plastic seat Tank Crack Repair

tomhall

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I too have a small crack in my seat tank. It is the plastic tank that replaced the fiberglass tank. ( I think we need an after market seat tank manufacturer ! ). Any way, I have a 1 1/2 " horizontal crack on the top surface of the tank directly between the two conical verticle" holes ". I drilled the ends to stop the travel and tried a two-part material that was to dry somewhat flexible; that didn't work. Now I have " Seal All " and a Permatex product both saying " gasoline resistant ". There is also a Dow Corning 730 silicone, 3 oz. $ 80 ! Because the crack only leaks when I have over 12 gallons of fuel, it's not an issue on short flights. But a crack is a crack and I want it fixed. Anyone have experience or comments on these products ? Thanks Tom T. Hall in MN
 
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karlbamforth

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Tom,

I don't know anything about your seat tank so take this as passing advice only.

No matter how you repair the tank it will never be perfect.

In the even of a heavy landing or crash your body weight multiplied by the G loading will crush the tank causing it to fail at the crack location and possibly spraying you and the rest of your aircraft with fuel.

Surviving a crash only to burn in the wreckage is not good.

Just for peace of mind splash out on a new tank. (pun intended)
 

Chuck Roberg

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bmoore2156

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Tom,
I think Brian tried something like this and it didn't work very well.
You might read through his thread to see what all he tried. I very badly want to build a aluminum seat tank for mine to get rid of the heavy fiberglass one. The good thing is my fiberglass one doesn't leak and is more comfortable than the plastic ones. I am not sure who built it and if they are still available.
Brian ended up ordering a new one from RAF. If you don't like to have your machine tore apart working on it all the time, it might be the best option.
My machine also came with a spare high back plastic tank that I would be willing to part with.
http://www.rotaryforum.com/forum/showthread.php?t=25735
Brad
 

Jamie Cleary

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Tom, Depending on the type plastic you should be able to plastic weld
it, I have repaired many things and if you take your time and prepare the area
properly it should take care of your problem, if you were close by I would fix
it for you. If you know someone at a bodyshop they should be able to fix it for you just be sure you identify your material and get the proper rod , if
you buy your own kit practice on some scrap before trying it out on the tank
it takes a little practice to get it right.
Hope This Helps!
 

turbo

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my vote is for marine-tex. call around to boat places like west marine. it comes in white or black and will bond to anything prepped, and harden like steel. it is all i use for things like this. good luck.
 

LARRYEBOYER

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Tom. Hope all is well with you. I agree with Turbo. I would suggest marinetex. I had a leak in a plastic tank on a boat and the boat dealer suggested marinetex. It did work!
 

turbo

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also, a nice thing about marine-tex is to wait for the stuff to get hard like putty, then you can finish forming it with your finger. use tape so the stuff will go were you want it. :peace:
 

tomhall

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Thanks guys for the input. I think what I will do is buy several of the products you recommended and test them on something else first. My concern with anything that sets up hard, is the vibration environment the tank lives in. I am hoping for something that will be somewhat elastic. I will post again after the tests. Tom T. Hall
 

Kevin Morris

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This stuff is made for fuel tanks and remains flexible. It seems to stick to everything- fingers, tools, etc.

http://www.aircraftspruce.com/catalog/appages/ps890.php

Think about applying a mechanical patch to spread the load over the damaged area and seal with Proseal.

I'm with Karl above - might think about a load spreading piece instead of just a patch bonded over the top of the tank to spread butt load on impact. Burning sucks.
 

Heather Poe

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Think about applying a mechanical patch to spread the load over the damaged area and seal with Proseal.
Kevin and Tom,
Many people had problems with the ethanol alcohol dissolving Pro-Seal in their Sparrowhawkshttp://www.rotaryforum.com/forum/showthread.php?t=23496. I am going with JBWeld for mechanical strength, followed by KBS tank sealer in my build.
Heather

"Gold Standard may be used on steel, aluminum, and fiberglass tanks."
http://www.kbs-coatings.com/Tank-Sealers_c_7-1-0.html
"impervious to all fuels, alcohol additives & most solvents"
http://www.kbs-coatings.com/Auto-Fue...-Kit_p_34.html
 

willisbr

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Tom, I'm the Brian that he was referring to. You will not he able to repair it permenantly. The plastic tank is made of linear polyethylene. Likely, it is already saturated with gasoline as well. No glue, bond, weld, etc will ever sustain. I have spoken with the actual manufacturer in Canada and have been advised that if a crack develops it's best to replace. I bought a new one and had it fluorine treated. Considering the location of yhe crack, I would replace anyway. Structural integrity etc. Gas especially with ethanol will continue to permeate and soften linear poly over time. It will only get worse. Search for the post on my tank adventure in here. Good luck. Pics of your tank?
 

Timchick

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How expensive would getting an aluminum tank custom made be? Seems like it would solve the problem permanently.
 

willisbr

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At the same fuel capacity, The quotes I got were more than a new plastic. The RAF tank form is funky nightmare. Talked to the guy that cut out the bottom to fit aluminum tanks and he said it was jacked. If one knew how to roll and hammer mold aluminum like the pros that make motorcycle tanks, it would be a nice but take for ever. May be heavier too. It's big.
 

Sheldon

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Tom, Depending on the type plastic you should be able to plastic weldit, I have repaired many things and if you take your time and prepare the area
properly it should take care of your problem, if you were close by I would fix
it for you. If you know someone at a bodyshop they should be able to fix it for you just be sure you identify your material and get the proper rod , if
you buy your own kit practice on some scrap before trying it out on the tank
it takes a little practice to get it right.
Hope This Helps!
Harbor Freight tools sells plastic welding kits....
 

NoWingsAttached

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Do not use sealing products if you can heat and melt it together. Being a crack, it should be easy, but drilling it was the wrong thing to do. Now you have created a void. With the two edges of the plastic in contact, heat welding is easy. Filling a void doesn't work very well, the plastic retreats, it wants to be with more molecules just like itself. I had a rebuild thread on here for my Air Command that I trashed, it uses the black-plastic, rotational-molded seats and it was very easy to heat and weld. When I was done you couldn't tell there was ever a crack.

No matter what you use to "bandaid" patch it together, unless it is melted - either chemically or with heat - it is going to fail eventually.

If you are willing to try heat melting, you must drain the tank completely of course. I had the luuxury of 18 months of letting mine sit before welding it together. Since you have been using yours, you should probably fill the tank with water, drain that, leave the cap off and let it sit in the sun all day to evaporate the water.

Use a propane torch. and keep the flame constantly moving rather quickly back and forth around the crack, so you don't heat up the plastic too fast. It only needs to get to 320 - 340*F. Have a 1" putty knife handy, and use that to work the soft plastic together, smoothing the rough edges of the repair until it disappears. If I find the time to locate the pics on my old ACT rebuild thread, or dig out the ones I have on my other laptop, I'll post here for you.

If this thing cracked all by itself, with no blow to it to create the crack, then the wrong material was selected to mold the tank in the first place, and cracks will continue to appear as it ages and loses elasticity. Rubber is used in formulating the plastics compounds used most often in rotational molding objects like this, and it sounds like the plastics shop/gyro designer used too little rubber in the formula.

Good luck.
 
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NoWingsAttached

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Here we go. Unfortunately I can't locate the photo of the crack before I started welding it, but even in this first photo you can see the difference in the "shiney" look of the plastic as it reaches working temps and loses its dull surface look. When heating, look for signs of any change in surface texture or reflectance to indicate it is ready to work.
 

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Heather Poe

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Metal Tanks

Metal Tanks

The Home Shop Machinist http://www.homeshopmachinist.net/media/images/index/mediaid/1189, has an excellent article called "Methods for Metal Fuel Tank Development and Fabrication, November-December 2010, pages 12 - 23. Although I am not going this route, it looks like it would not be any harder than building pieces of an aluminum aircraft.
 

lanichol

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The Home Shop Machinist http://www.homeshopmachinist.net/media/images/index/mediaid/1189, has an excellent article called "Methods for Metal Fuel Tank Development and Fabrication, November-December 2010, pages 12 - 23. Although I am not going this route, it looks like it would not be any harder than building pieces of an aluminum aircraft.
Heather, Had problems with the link as It maybe that I do not have a subscription.

Found the back issue online. Seems to be back-ordered.
https://secure.villagepress.com/store/items/detail/item/2234
 
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