Skervey HalfDork
7/13/18 10:09 p.m.

Hey guys its been a while! Started on a dream build a few months ago! Its a motorized bike in the form of an early motorcycle/board track racer. 

Anyway I just “finished” welding a custom tank and im no welder but it came out looking good! I put a air hose in the tank and wet the outside with windex and found holes... 9-10 on the seams but a lot around the filler neck tube. The metal is thin and it buns through easy. I spent 2 hours tonight grinding the welds and trying again but it only seems to be getting worse. I had some luck along the seams but the filler neck it bearing me! 

So what do you guys think of gas tank sealer kits to fill the tinny pin wholes in the filler neck and keep the gas tank safe for years to come? I would love to do it the right way but im only making it worse at this point. 

Some info, im using a 220v mig welder, 5” exhaust tube, filler neck from the motorized bike kit, and iv had little experience welding this project was to help me learn more!


pic are always a must! But I cannot upload them from my phone to flicker to this thread. Check out my instagram @petrol360 it looks really cool! Just needs to hold gas and bit catch on fire!


CJ Reader
7/13/18 11:23 p.m.

Have you considered flowing braze over the area or even lead? Either should seal the pinholes and are unlikely to make the problem worse. 

Of course, if you do either, your welding is likely over - at least that area.

Ransom PowerDork
7/14/18 12:47 a.m.

In reply to Skervey :

You should be able to load pics directly to the thread now, speaking of "been a while!" :)

NOHOME UltimaDork
7/14/18 6:46 a.m.

Fluid tight welds are tough with the MIG. The solder is a good idea and sealing is also as long as the sealer is approved for the ethanol in today's fuels.



Skervey HalfDork
7/14/18 10:20 a.m.

Yes I knew mig was going to be hard but you learn through struggles. But it just getting worse so I need stop before i burn holes through it. 

Brazing is an amazing idea! That sounds like the ticket then seal the tank. I will make sure it is a good sealer for ethanol as well!

NordicSaab Dork
7/14/18 10:23 a.m.

As others have said, getting a non porous MIG weld on thin material is going to difficult if not impossible.  I think several viable solutions have been mentioned, I think it mainly depends upon what esthetic you want.    

NOHOME UltimaDork
7/14/18 11:03 a.m.

It can be done. The trick is to weld real hot. You do the single dot technique where you weld on the face of the last dot, but you have to be hot enough to really melt the  bead you are welding on.


Wipe the weld area with acetone before you run the bead. ANY contaminants will contribute to a pinhole


CJ Reader
7/14/18 3:33 p.m.

So far as I know, both solder and braze are impervious to ethanol, so long as you have a good bond...  start with clean metal - use acid flux for solder and tin the area before building up with lead.  If you need to shape it, build up some lead - a little torch goes a long way - and shape with a wooden paddle coated with bees wax (this from the old body man who showed me how  40 years ago). Use brazing flux for braze,  but don't get too hot... 

I believe that many old OEM tanks had soldered seams and I seem to recall that the filler tube on a couple tanks I refurbished were brazed in place.

After all of the work it looks like you have done, seems a shame to use sealer inside your tank.

Skervey HalfDork
7/14/18 3:43 p.m.

Thanks NoHome,

thats what iv been doing and it worked well on the seams but the fill neck is so much thinner then the body of the tank it just burns through before I can get a good tack. Even with an air hose blowing to cool after every few spots. Guess I need to do some reading on brazing!

Iv shot video of the full build that I will post up once its finished up!

wlkelley3 UltraDork
7/14/18 10:19 p.m.

Came here to say exactly what CJ said. A lot of OEM tanks are brazed and/or soldered.


fasted58 MegaDork
7/14/18 10:38 p.m.

You can TIG over MIG providing the welds are clean yet. Easier to control heat w/ pedal on thinner sections.

You could probably just go over present welds providing there's enough weld there already and blend/ burn it in. But I haven't seen it.

Donebrokeit SuperDork
7/15/18 7:54 a.m.

I seen to recall a company that made a liquid sealer for gas tanks, not sure how well I worked or the costs.



44Dwarf UberDork
7/15/18 1:46 p.m.

Just use Caswell platings gas tank sealer and be done with it.  BE SURE TO FOLLOW the instructions.  Once it cures no chemical can remove it or soften it.

Appleseed MegaDork
7/15/18 8:07 p.m.

A nice place to find original style tin/lead is any place that has stained glass window supplies. I picked up 37/63 solder at Hobby Lobby. Melts like butter. No fighting it like that modern crud.

Rusnak_322 Dork
7/16/18 2:26 p.m.
44Dwarf said:

Just use Caswell platings gas tank sealer and be done with it.  BE SURE TO FOLLOW the instructions.  Once it cures no chemical can remove it or soften it.

Not so sure about that.

here is the Caswell coating that was put on a brand new tank that never had fuel in it. Installed by the dealer who did lots of them as Warranty replacements.



Keith Tanner
Keith Tanner MegaDork
7/16/18 2:33 p.m.

I had this problem with my Locost tank. I used a Kreem kit from a bike store and the problem was solved. That was back in 2006 or so and it's still holding up.

Skervey HalfDork
7/16/18 8:35 p.m.

I picked up some silver solder made for metal at the store. It has flux built in but not enough. Gave it a try with a propane torch but it wasn’t flowing. Going to go back and get some flux and use map gas next time!


thanks for the input. Once I get it sealed up im going to use a gas tank sealer. Guys at work talk about a local guy that burned his house down due to a leak on his bike... 

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