Problems welding motorcycle gas tank

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Hey guys.After reading through all of the recommendations on what type of gas to run I went with Co2 for my century 180.I had to move a petcock bung on a motorcycle gas tank. Probably a bit over my head as I'm as amateur as they come. I cut the bung out with a wolesaw, debrazed the bung, and ground every spec of brazing off with a dremel. Then cut a piece of 16 ga steel to fit the hole. Next I welded the new steel in, then drilled out for the bung, and welded it in.Everything looked good. My welds were a little sloppy, but everything seemed solid. Good penetration, color around the welds, etc. I ground everything down, and didn't see many pin holes, or cracks. The ones I saw I rewelded, and reground. Then I pressure tested it.... Pumped it up to about 3psi, and used soapy water. Man did it leak a lot! Upon closer inspection there were some very very tiny holes, and some areas that seemed to leak right out of solid steel. I welded over the leaks all around, and this time didn't grind anything down. There are 2 leaks left. They are in a tight spot where I can't get a real good angle on them. I've ground them down to base metal, and rewelded 5 or 6 times now. I've gone from a voltage of 2 to 4 (of 5) on my little welder. Everytime I reweld those spots they leak at the far edge of the weld. This is only 1/8" away from the petcock bung, so I can't get in from another angle. It seems like it's just not burning in on the far edge, but I'm almost maxed out on voltage.Is there anything else I can do to get these to stop the leaking? A friend suggested drilling a hole, then welding in the hole which sounded good to me, but I haven't tried it yet.I don't want to try to braze the holes because the tank is already painted, and I think the added heat from brazing will damage the paint. Welding, I do a small area, stop, do a small area, etc, and that seems to keep the heat in the area I'm working on.My welder:Century 180 Wire feed welder.
Reply:Put on your rain gear, it's coming..................popcorn....................200amp Air Liquide MIG, Hypertherm Plasma, Harris torches, Optrel helmet, Makita angle grinders, Pre-China Delta chop saw and belt sander, Miller leathers, shop made jigs etc, North- welders backpack.
Reply:Originally Posted by [IEbola Monkey;504655]Hey guys.After reading through all of the recommendations on what type of gas to run I went with Co2 for my century 180.I had to move a petcock bung on a motorcycle gas tank. Probably a bit over my head as I'm as amateur as they come. I cut the bung out with a wolesaw, debrazed the bung, and ground every spec of brazing off with a dremel. Then cut a piece of 16 ga steel to fit the hole. Next I welded the new steel in, then drilled out for the bung, and welded it in.Everything looked good. My welds were a little sloppy, but everything seemed solid. Good penetration, color around the welds, etc. I ground everything down, and didn't see many pin holes, or cracks. The ones I saw I rewelded, and reground. Then I pressure tested it.... Pumped it up to about 3psi, and used soapy water. Man did it leak a lot! Upon closer inspection there were some very very tiny holes, and some areas that seemed to leak right out of solid steel. I welded over the leaks all around, and this time didn't grind anything down. There are 2 leaks left. They are in a tight spot where I can't get a real good angle on them. I've ground them down to base metal, and rewelded 5 or 6 times now. I've gone from a voltage of 2 to 4 (of 5) on my little welder. Everytime I reweld those spots they leak at the far edge of the weld. This is only 1/8" away from the petcock bung, so I can't get in from another angle. It seems like it's just not burning in on the far edge, but I'm almost maxed out on voltage.Is there anything else I can do to get these to stop the leaking? A friend suggested drilling a hole, then welding in the hole which sounded good to me, but I haven't tried it yet.I don't want to try to braze the holes because the tank is already painted, and I think the added heat from brazing will damage the paint. Welding, I do a small area, stop, do a small area, etc, and that seems to keep the heat in the area I'm working on.[/I]
Reply:Originally Posted by dave powelson1-You're correct-you're in-way over your head. Doing seal tight welding with a MIGain't that easy. Tanks are stressed units anyway--welding with mininum heat inputis needed for a bunch of reasons. For that and other reasons-brazing usually is not an option.      If saving this whacked up tank is important, then take it to a shop that does tank repair/restoration and has TIG.If this tank can be saved-more than likely it will require delicate washing andwelding with TIG--by one that has some clues.2-Repeated leaks at the weld edge are either or both-cold weld leakage orcorrosion/pitting of tank wall is cracking from the stress of weld contraction3-3 PSI is too much for tank of unknown condition. Slight positive pressure is allthat's needed.4-Examining the inside of the tank--for corrosion/pitting--PRIOR to any repair is the first step. Second is pressure test of the tank.Some tank designs are really good at corroding out, more than others.Lots of tanks crack and leak at the tank mounting tabs. There's decent repairsand fixes for that, too.5-The pundits who make blanket recco's of just sloshing the tank with sealantto make it mechanically 'strong' are less than correct. Sloshing a tank after making itmechanically pressure tight for corrosion prevention is one thing. 6-That 180 Mig apparently is a 220v machine--too big for tank repair. A 120 volt machine can be throttled down much lower in amps than a 220--something that is not understood. Sometimes, some of the repairs done with light MIG, then grinding/ washing the starts and stops with TIG--depends on the deal.7-I've only done around 150 cycle tank repairs/restorations, including exquisitely painted, expensive ones and things for 'the brotherhood'.
Reply:Thanks for the replies guys. Originally Posted by bert the welderPut on your rain gear, it's coming..................popcorn....................
Reply:If the tank is 'sound', then the pressure leaks may be from cold starts, lack of edge wetting, incomplete fusion. Firing off, then quickly running the puddle back aways, past the 'fire off' point--then come forward over the 'fire off' point, can help stop cold starts. The bead width needs to be more, maybe 50% to 100% -than it's height, with nicely faired, wetted edges for sealing. Getting decent at seal welding with a MIG takes more than 5 minutes of practice.Trying to wash over a cold start on MIG, without first grinding a length of that start out--is very problematic on thin gauge.That's another reason for TIG, or tiggin' the whole thing. Ramped up tank pressures invite damage to the tank in addition to tank rupture.Blackbird
Reply:Thanks again for the reply Dave.I think I understand what you mean about cold starts... 1 step forward, 2 steps back, then move forward so to speak right?The last pass I did on this final spot was about 1" long. I started before leak #1, and ran past leak #2. both of them leaked less, but were still leaking, and again on the edge away from where I was welding. Not the "nicely faired, wetted edge" that you describe. This area goes from flat to vertical, and has quite a bit of weld built up on it.  I've ground down to the base metal on the bung, but only to what I believe to be solid weld on the tank side.  Could I just not be hot enough in this area because of the build up?I know that I'm not going to learn this overnight. This is all part of what will be a very long learning curve.My welder:Century 180 Wire feed welder.
Reply:Originally Posted by Ebola MonkeyThanks again for the reply Dave.I think I understand what you mean about cold starts... 1 step forward, 2 steps back, then move forward so to speak right?The last pass I did on this final spot was about 1" long. I started before leak #1, and ran past leak #2. both of them leaked less, but were still leaking, and again on the edge away from where I was welding. Not the "nicely faired, wetted edge" that you describe. This area goes from flat to vertical, and has quite a bit of weld built up on it.  I've ground down to the base metal on the bung, but only to what I believe to be solid weld on the tank side.  Could I just not be hot enough in this area because of the build up?I know that I'm not going to learn this overnight. This is all part of what will be a very long learning curve.
Reply:Originally Posted by Ebola MonkeySorry, the machine I have is the only machine I have. I bought it in stead of a 120v machine because of all the "120v welders are useless" threads I read here.
Reply:"wash over" sounds about right. For heat, I did do a bunch of test welds on coupons of the exact same material before I started. 90% of the job worked out great on the same setting. I got too slow at 1 point and burned a hole, but filled it in with no problems. I'm not sure if I should jump up to .30 wire though, since it is thicker here. I couldn't get to it at all today, maybe tomorrow I'll grind everything down as far as possible, then try again.My welder:Century 180 Wire feed welder.
Reply:I did end up getting the tank sealed up. Spent a lot of time grinding, and rewelding. 1 particular spot I ground down the final time, and was getting super fine bubbles, almost like shaving cream fine (using soapy water). I grabbed the dremel with a pointed diamond tip, and started grinding in, and sure enough a small pocket opened up. I cleaned it out real good, and rewelded again. Problem solved.I don't think I'm gonna grind any of my sloppy booger welds down for fear of opening another can of worms. Again, I knew I was in over my head when I started. Thanks for any and all help.My welder:Century 180 Wire feed welder.
Reply:Sometimes some flux and silver solder will get the job done just as well as the tig, and leaves you with a surface that is almost paintable "as is".Miller Syncrowave 350Millermatic 252/ 30A spoolgunMiller Bobcat 225g w/ 3545 spoolgunLincoln PowerArc4000Lincoln 175 Mig  Lincoln 135 Mig Everlast 250EX TigCentury ac/dc 230 amp stickVictor O/AHypertherm 1000 plasma