sealing a gas tank weld? 3M 5200?

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Hi thereI was making some modification to the inside of my gas tank, then welded the top back on.I tigged everything and it seems like there are no leaks but I would like to just put something over the weld just incase. This is on the top of the tank.Has anyone heard of 3M 5200? Can I use that over the welds....or what would you recommenendThanks for any advice Attached Images
Reply:You can use this stuff; http://www.kbs-coatings.com/Howie-Ho...k_ep_51-1.htmlOr better to call the local radiator shops and see if one does it with the aircraft type tank sealer.Matt
Reply:ok i will check that out thank you
Reply:I have to ask, why did you cut a hole in your fuel tank?John
Reply:well since you asked I cut it open to put a baffle in it as the factory one has a poorly designed baffle. This car goes to the track and when going around corners the gas flows away from the pump pick up causing the car to bog.
Reply:Probably be better to get someone who knows how to tig weld, to weld it up for you than to rely on a bunch of sealants.5200 is not designed for this application.I can almost guarantee you, based on what I can see, that that tank WILL leak.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:http://www.aircraftspruce.com/menus/...ksealants.htmlGet some B2, mix until evenly gray, and coat as thick as you like after cleaning the area with acetone or similar oil-free solvent.I love the stuff. We used to get expired tubes from bench stock and use it for all sorts of automotive stuff. Awesome gasket sealer/maker if you don't plan on removing the part. Great wetting, wear gloves when applying.
Reply:Thanks Farmall, i saw sundown username then just skipped right to your post i'm going to try that b2
Reply:Originally Posted by hotpawsI tigged everything and it seems like there are no leaks but I would like to just put something over the weld just incase.
Reply:Well this is the top of the tank where it will only see fumes it seems to hold water, I don't have a air compresser to pressure test it so i can only say it holds water when upside downIts my first time welding on a gas tank the one guy says he guarantees it leaks buy looking at the pic lol but look who it is does he even have a job?, well  it doesn't leak....lol but its my first time so just want to make sure and go over it with something. I even went over the welds with the torch.Do i have the confidence that its sealed up....yes i do....but hell yes i want to still put something over it.Did anyone see all the sealers for tanks they sell on the link farmall posted? **** I wouldn't want to fly in a plane that had a tank with sealer on it?Not very helpful Jay o
Reply:Thanks Hotpaws,If you think that looks anything like what a decent tig weld should look like, then you've still got a lot to learn.I've got seagulls that land on my pier and lay down a more consistent "bead" than that.If you can't produce a tig weld that will pass a pressure test, you shouldn't be welding on a fuel tank destined for a "track" car.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Check with where you run and make sure they allow a tank sealer.  On a solo/DE type street car it may not be an issue but if it's a purpose built race car they may not allow it through tech.
Reply:Originally Posted by SundownIIIThanks Hotpaws,If you think that looks anything like what a decent tig weld should look like, then you've still got a lot to learn.I've got seagulls that land on my pier and lay down a more consistent "bead" than that.If you can't produce a tig weld that will pass a pressure test, you shouldn't be welding on a fuel tank destined for a "track" car.
Reply:Originally Posted by dstevensCheck with where you run and make sure they allow a tank sealer.  On a solo/DE type street car it may not be an issue but if it's a purpose built race car they may not allow it through tech.
Reply:Shortage of work has never been a problem, nor do I think it will be in the future.There may be a lot of "welding machines" sitting in people's garages, but that doesn't mean that there are more "welders" out there.I just hope you're not out there making what you consider "structural welds" on that race car.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Originally Posted by hotpawsIts a steet car and no one would ask you to drop a stock tank.
Reply:Originally Posted by SundownIIII just hope you're not out there making what you consider "structural welds" on that race car.
Reply:Water is no good for initial testing but diesel would be what we use at work.  When we diesel test, we spray the weld and let it sit for 4 hrs min. If any repairs are made then they are tested again. The tanks are eventually tested with water but then they are allowed the sit for more then a week.  So maybe get a little diesel, seal up the tank and slosh it around let it sit and then check it.  Another option is if there is a way the adapt a tire valve into the cap that you use to seal up the tank and use a bicycle pump to fill the tank with air.
Reply:1-I agree with Sundown's observation of the quality of your 'first time' TIG welds........and both of us have welded--beaucoup tanks. A guy should be looking for good edgewetting, washing/backing up on starts and stops, no craters, etc. Lots of little thingsto look at when seal tight welding.2-Be aware that stock vehicle tanks in closed systems (which yours is) are designed for 2# max.pressure or vacuum. IOW-in testing a new-not a scab modified tank like yours--max. pressureshould be 2#. Don't even think about hooking this tank up to a buddy's air compressor. 3-You do not mention if you did any interior/exterior welding mod's to the baffle. If so,that adds more confusion.4-Static, no pressure, water testing can show 'no leaks'........but the much lowersurface tension of gasoline will find those 'no leaks'.Blackbird
Reply:dave powelson - your point about the interior exterior welding of the baffle....doesn't even make sense and has nothing to do with sealing the top of the tank. If you are confused about that we might as well be talking about bowling.Hey Jay O I tried the bike pump today and it worked great with soapy water. first a bubble came up from the top of the pump cap i was using as I just crimped the tube shut then i just welded it closed .......Then I saw no bubbles. Suprising how much air you can put in with 3 or 4  pumps of a bike pump.heres a video[ame]http://www.youtube.com/watch?v=2bfSClHYvZY[/ame]. Attached ImagesLast edited by hotpaws; 08-14-2010 at 03:23 AM.
Reply:Well son, let me give you some advice.Gasoline will leak in places where even water will not.I have known lot's of people that welded gas tanks - that were pressure tested and tested with water and when they put gasoline in them - they leaked.If you used a carbon steel rod when you welded the tank and the tank was carbon steel and not galvanized then the next step would be to solder the joints with a lead based solder and some flux and a copper iron and a torch or a oven to heat the iron.A long time ago, I had a friend who drove over his spare tire carrier and punctured a hole in the bottom of his gas tank on his 1978 F-150 truck.  A mechanic who worked at the truck garage where he drove truck repaired his tank for him in the back garage.   He straightened out the sheet metal and he put some pennies over the hole and he soldered the hole shut and that was 30 years ago and the tank has never leaked.He still has the truck and he drives it all the time.Tig welding is fine - if you know what you are doing, because you get 100 percent penetration.  Even if the weld was messed up a little bit, you could have took the torch and gone back over it and repaired the leaks.  But most times the galvanized metal will give you problems and the fumes are not good for you.  So soldering is the best way to repair a tank - after the butcher job that you did on it.PS - they make something called a fuel cell - that has a plastic or rubber bladder inside of it and you can put foam cubes inside of the tank to control the slosh.I have a dirt late model and we go 90 miles an hour in the turns - with no problems and no baffles in the tank.http://www.rciracing.com/
Reply:At some point you have to say it's good enough.  If it passes the pressure test with air then it has to be good enough.  I mean you could solder over everything.  But is that good enough?  Solder is a finicky thing.  How about soldering and sealant.  What if some chemical in the gas attacks the sealant?  Well lets line the tank with a bladder.  Come on, we can nit pick every repair to death but at some point somebody has to come up with something that they can call acceptable.
Reply:Sorry buddy - but you are wrong.In these new cars, there is a pump that puts air into the tank, that measures how much air escapes and when there is a leak, it sets off codes in the computer that turns on the check engine light and causes the vehicle to fail an emissions test.I worked on a Jeep Liberty last year for my brother in law that is a truck mechanic.Their check engine light came on and I went through the entire vehicle with a fine tooth comb until I found a bad fuel line.You could reset the codes, fill the tank, drive the vehicle until it got down to half a tank and then the check engine light would come back on.  It would suggest that you change the gas cap.   It knew that there was a leak or a loose gas cap.We are not back in 1976 - where a tune up was points, plugs and condenser like 30 years ago.
Reply:Good thing this car has nothing like that its a 22 yr old car and there is no pump that puts air into the tank lol.There are no more emissions equipment either.....and it doesn't have to go for e-test as its not driven on the street. Fuel cells are nice but foam isn't as good as a baffle and a fuel cell set up is heavier than a modified stock tank.....and most dirt track guys couldn't build a safe fuel cell set up to save their lives. Come on lets get real these guys run their rear bumper bars to their main hoop and down tubes I did tig it and it took forever because I was going back and over lapping it took forever lol....then I went over it with the torch, yea the galvanized was nasty , i hate galvanized but I had my respirator and huge flip down hood with a celing vent with a hose to suck and fumes....i was still holding my breath Why do Aircraft use all this stuff Booger Welder?http://www.aircraftspruce.com/menus/...ksealants.htmlIts true you go 90 through the turns but try turning right at 90 then turn left and repeat that at 90 with a 1/4 tank and get back to meLast edited by hotpaws; 08-15-2010 at 02:06 PM.
Reply:If you use one of the aviation "sloshing compounds" (fuel tank sealants) be aware that some of them do not tolerate alcohol in the fuel. If your fuel contains alcohol the sealer can deteriorate.