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  #381  
Old 03-05-2013, 11:26 PM
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TheBandit TheBandit is offline
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Thanks Graham! I really like cleanly routed tube. After getting it in, there are some things I might do differently but it's hard to picture it until you get it into place.

Here is where the fuel line connects to the Corvette FPR. I have not mounted the FPR yet; I just need to drill and tap or rivnut a hole in the frame. You can see the previous owner relocated the shocks and plated over a portion of the frame where this will mount. I'm not sure what this area looks like on a stock Nova.



I started working on putting the fuel pump in tank. I am using a Tanks Inc PA-4 setup which includes a Walbro 340 (255lph) pump, hanger, and tray. Before I show you how I put it in, here's a preview of what it looks like:



Here is where I started with the hanger mounted upside down.



I positioned it so it would position the pump in the deepest part of the tank. This is actually toward the front of the tank, near the original pickup.



I made a hole in my tank initially using a jigsaw, but I switched over to hand shears because I ran into some internal baffling I wasn't expecting that threw the jigsaw all over the place. I did my best to flatten the ribbed sections of the sheet by clamping it between some thick metal plate using c-clamps, but that only did so much. Then I drilled a hole pattern and eventually "spot" welded the backup flange to the tank by drilling holes from the top and filling them with weld. I went over that with a flapper wheel and this is the UGLY, but functional hole I was left with.



One of the things I was really hoping to accomplish by positioning the pump here was to be able to use a factory sending unit for the fuel level. Here you can see the inside of the tray through where the original sending unit mounts.



I cut off the tubing from the old sender and drilled a hole so I could run a draw string to actuate the float. Then I put the sender in and confirmed it could move unobstructed. This sender wasn't working right anyway, so I plan to replace it.





Once the mounting was figured out, I assembled the hanger, pump, pickup, etc. I had to cut the mounting bracket down pretty far. The tank is about 7" tall, but if you look closely you'll see I ended up angling the tray about 5 degrees to match the slope of the tank. I am not sure what to think about routing the return line directly next to the pump like Tanks Inc has it setup.



And here it is, just about ready for final install. I need to clean the tank out really well before I finish it up, but you get the idea.



I was originally planning to recess this into the tank to provide fitting clearance, but I have another idea I'm going to try. Still plenty of work to do...
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  #382  
Old 03-06-2013, 01:14 AM
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I was originally planning to recess this into the tank to provide fitting clearance, but I have another idea I'm going to try. Still plenty of work to do...
Consider an access panel in the trunk floor.
Then put the clearance in the cover.
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  #383  
Old 03-06-2013, 11:58 AM
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Any ideas for things I could make a raised access panel from? I was thinking maybe a shallow transmission pan or a cookie sheet if I could find something suitable.

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Last edited by TheBandit; 03-06-2013 at 12:00 PM.
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  #384  
Old 03-06-2013, 12:08 PM
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Any ideas for things I could make a raised access panel from? I was thinking maybe a shallow transmission pan or a cookie sheet if I could find something suitable.
A small (6") SS Frying pan (local Thrift Store)would do the trick.
Hammer form the piece you cut out and weld on a tab or 12...
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  #385  
Old 03-10-2013, 08:35 PM
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Anything worth doing right is worth redoing. I couldn't bring myself to cutting the trunk floor and decided lowering the tank wasn't going to work out, so I am starting over with recessing the pump. I bought a pre-fabbed recess tray from the local department store - $5 and it's teflon coated.







Little more work to do. It's a start though.
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  #386  
Old 03-10-2013, 09:53 PM
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You crack me up! You are pooching with the tank because you don't want to ruin the trunk floor and you put an LS in it
All kidding aside.

Ok, the catch is that your entire pump flange and fasteners will now be below the level of the fuel in the tank and this makes sealing of the pump flange critical because:
With the pump flange at the top of the tank there is in theory no pressure (head). However, with this arrangement your have whatever the depth is, plus the theoretical (real pressure) and basically. I've seen leaks where there should be nada in this scenario and it turned out to be the threads in the bolts. Just a word to the wise be certain of the sealant you use on the treads, generally the gaskets tend to work fine.

Oh and be sure to remove the Teflon well out of the predicted HAZ.

E
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  #387  
Old 03-11-2013, 11:43 AM
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Originally Posted by entropy View Post
You crack me up! You are pooching with the tank because you don't want to ruin the trunk floor and you put an LS in it
Trust me, I fully appreciate the irony! I can't figure it out - I had no issue cutting up the subframe or putting a modern engine in, but when I started laying out the cut for the trunk floor I suddenly became apprehensive. There's something a bit more permanent (psychologically) about cutting up the body of the car whereas the suspension, the engine, the tank - that can all be replaced easily if needed. I guess there's a sense of reversibility with the other mods that I don't have with cutting up the body. Silly I know.

So what would you recommend for sealing the threads?
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  #388  
Old 03-11-2013, 12:18 PM
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They make replacement trunk tub sheet panels
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  #389  
Old 03-11-2013, 01:58 PM
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Trust me, I fully appreciate the irony! I can't figure it out - I had no issue cutting up the subframe or putting a modern engine in, but when I started laying out the cut for the trunk floor I suddenly became apprehensive. There's something a bit more permanent (psychologically) about cutting up the body of the car whereas the suspension, the engine, the tank - that can all be replaced easily if needed. I guess there's a sense of reversibility with the other mods that I don't have with cutting up the body. Silly I know.

So what would you recommend for sealing the threads?
I recommend a blind nut ring...
I would make a 1/2" thick ring with 'Blind' 10-32(or =) threaded holes to attach to the inside of the tank, welded to the bottom your pan B4 you weld your pan in; thus I would have sealed the treads and be only relying on the gasket to seal the assembly {You must have zero distortion so alternatively a Flat head screw or 4 could be a better choice to hold the nut ring - red lock-tite}. You should TIG your pan in-place and you must pressure test it; that is what I would do...
What I would really do at this point is go buy (Fab) a tank with a sump on the bottom of the tank and pull my supply out of it and plumb it into an external pump because I've had enough experience with in-tank pumps to know that there is no real benefit and many-many drawbacks when running street gas or anyplace where the ET is not measured in tenths (and even then I'd run external!)

If I was in your shoes I would have cut an access panel in the floor AND I STILL WOULD (dropping the tank to service the pump or sock is just dumb) because I know as an investment in the real world this car is a depreciating asset (unless I sell it soon and then I'll not break-even if count my labor); it is just an old GM product, that I may be allowed to drive another few years in CA before for various obvious reasons my baby will be banned and all I can do is polish it in the garage once I have certified that there are no petroleum based chemicals in it...

I ain't picking on you or doing that Ford/GM thing that I find hilarious...
Understand that of all the vehicles GM ever has built yours is one of the 3-4 I would own (7'dz Corvette, Buick GSX). It is just that I can see the paradigm changing.

Pax
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  #390  
Old 03-11-2013, 03:13 PM
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I would love to build a tank from scratch and maybe I still will when this thing weeps or drips fuel from every booger weld I stitch it together with, but in the meantime I have seen a number of people modify their tanks in similar fashion with no reported issues. I like your idea of a blind threaded plate which could be welded in, but would it be worth the effort? Surely this can be sealed with a fuel resistant sealant.

The main reason I want an in-tank pump is to reduce or eliminate noise. I hate the winy sound of an electric fuel pump.
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  #391  
Old 03-11-2013, 03:28 PM
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I would love to build a tank from scratch and maybe I still will when this thing weeps or drips fuel from every booger weld I stitch it together with, but in the meantime I have seen a number of people modify their tanks in similar fashion with no reported issues. I like your idea of a blind threaded plate which could be welded in, but would it be worth the effort? Surely this can be sealed with a fuel resistant sealant.

The main reason I want an in-tank pump is to reduce or eliminate noise. I hate the winy sound of an electric fuel pump.
The only way anything I said will be worth it is if you don't do it and it leaks
How will you hold the nuts in place inside the tank with enough confidence to allow you to take it apart (after you seal it) to get to the sock when you get that load of crap gas that you will eventually get....


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  #392  
Old 03-11-2013, 03:42 PM
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I have a mounting ring that is tapped, maybe 3/16" thick, that came with the hanger from Tanks Inc. On the previous installation, I drilled a couple holes into the top of the tank, filled them with weld to hold the ring on, and ground the weld flat to mimic a pair of spot welds. This time I will just tack it in a couple places on the bottom side. The screws will go through holes in the sheet metal into that mounting ring.
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  #393  
Old 03-11-2013, 05:04 PM
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I have a mounting ring that is tapped, maybe 3/16" thick, that came with the hanger from Tanks Inc. On the previous installation, I drilled a couple holes into the top of the tank, filled them with weld to hold the ring on, and ground the weld flat to mimic a pair of spot welds. This time I will just tack it in a couple places on the bottom side. The screws will go through holes in the sheet metal into that mounting ring.
That will work. I'd use a Teflon paste rather then tape
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  #394  
Old 03-13-2013, 05:24 PM
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To test for leaks, about what level should I pressurize this tank? I was thinking regulate to a very low level like 3psi and spray all the welds and fittings with soapy water, looking for bubbles. Alternatively I could put 3psi in, close a valve, and check for pressure decay over time.

I plan to MIG weld this back together. I do not have a TIG welder. I have 0.023 wire and 25% CO2/Argon mix, Millermatic 180 AS. Do I need to attempt continuous welds or can a series of overlapping tack welds seal it up?
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  #395  
Old 03-13-2013, 07:53 PM
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I don't have any MIG welding expertise to share, but for pressure testing, I would use a low pressure, in the 3-5 psi ballpark. I would be concerned about ballooning the tank if you go very high. When I pressure test stuff, I usually seal it off (or use a Schrader valve to fill) and leave it with a gauge attached for several hours. I'll squirt with 409 if there is a leak and I'm trying to locate it.

If you can get a gauge with a low range, it will help determine if you've lost air or not.
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  #396  
Old 03-14-2013, 09:13 AM
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I worked in the HVAC industry for years where we did A LOT of leak testing (0.012" wall copper tube coils at over 600psi). For pressure testing I would recommend a little higher psi then the 3-5 mentioned. For your initial leak testing, the 3-5 psi is OK, but there still might be a leak if you feel that it is OK at that pressure. Once you feel that the welds are "leak free" at that LOW level of pressure, I would bump it up to about 30 psi and check again for leaks. Just make sure that the filler neck, vents and all other openings are sealed well before checking for leaks. The tank is strong enought to withstand the 30psi and should not "balloon" at all at that level of pressure.

For your welding, the MIG is fine, I would jump around the flange with a series of short overlapping welds to minimize the distortion of the sheetmetal.
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  #397  
Old 03-14-2013, 10:50 AM
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Assuming the tank is about 24"x36" at 30 psi that's about 26,000lbs of force trying to rip the tank apart at the flange joint. I'm pretty sure if it doesn't rip apart it will probably baloon. there is a big difference between a 1/2" round tube and a tank.

I wouldn't pressure test it at all. Just fill it with water and let it sit overnight. If it leaks, you'll see it.
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  #398  
Old 03-14-2013, 11:10 AM
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When testing a tank as mentioned it is really easy to get way to much pressure and damage the tank or yourself.
In testing any fuel tank I learned that the easy way to do it is to use a single layer of plane old "Masking Tape" to seal the filler neck and then use an air nozzle through the tape with just a few puffs to pressurize it; it is nice to have two people one to flow the water on the welds and one to apply the air. If the surfaces are clean the tape will stick enough to let you get to 3-PSIG which with soapy water is all you ever need, however a single layer of "Masking Tape" will rupture before the tank reaches any critical pressure.
FWIW I have had tanks pass the fill with water test and leak gasoline.
Finally with a MIG weld I would seal the interior of tank with an Alky proof sealant.Safety Glasses!

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  #399  
Old 03-18-2013, 03:49 PM
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Assuming the tank is about 24"x36" at 30 psi that's about 26,000lbs of force trying to rip the tank apart at the flange joint. I'm pretty sure if it doesn't rip apart it will probably baloon. there is a big difference between a 1/2" round tube and a tank.

I wouldn't pressure test it at all. Just fill it with water and let it sit overnight. If it leaks, you'll see it.
Not trying to start an argument, but to clarify a few things about this subject. I understand where you got your 26,000 lbs of force, but remember that typical 1018 mild steel has a Yield Strength of about 50,000 PSI and an Ultimate Tensile Strength of about 60,000 PSI. Since you must go above the Yield Strength of the material for it to deform (Balloon), you would have to apply more that 30 psi to the tank. I would not test at more than that pressure. Trying to find a bubble of soap from a small pin hole using very low pressure is time consuming, but that same hole will leak gas and vapor easily. From a safety point of view, the limit for air nozzles per OHSA is also only 30 psi if that nozzle should come into contact with your skin. I would always wear safety glasses when doing anything like this, even the soap blowing out of a small hole could get in your eye...

Clint is an engineer so he should be able to figure this testing out without much of our help. Like entropy, I would recommend using a gas tank sealer after you are satisfied your welding is good and the sealer would just help seal up any small pin hole leaks.
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  #400  
Old 03-18-2013, 04:47 PM
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Beware of comparing air pressure to material stress. The material stress is considerably higher than the air pressure inside the pressure vessel. Here is a primer on stress analysis for a thin walled pressure vessel http://www.efunda.com/formulae/solid...ure_vessel.cfm

It can get a lot more complicated for non circular cross sections. I can't get to my textbooks at the moment, but here is a potential resource.
http://www.gowelding.com/pv/square.pdf
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Last edited by TheBandit; 03-18-2013 at 04:53 PM.
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