Author Topic: Welded up my tank, how do I test for fuel leaks?? (Read 3608 times)

manjisann · « **on:** July 09, 2009, 07:36:26 PM »

So I was ambitious and decided to cut out the bad part of my tank and weld in a new section of metal. I know everyone says TIG is the way to go, but not having a TIG welder I decided to use my MIG welder. I stitch welded it and really think it came out well and will be fuel tight but I am not completely sure how to test it. I don't want to put gas in there to test in case there is indeed a leak, as then I'd have to clean it out to weld it again. I read where one guy used a bicycle pump to pressure test it, but I don't have a bike pump just a compressor. So here is the big question, if I set my regulator to 3-5psi, would I be safe? I just don't want it blowing apart on me and maiming or worse killing me. I can thread a 3/8 fitting onto the petcock area, but I am not sure how to plug the fuel hole, since it's not a perfect circle.

Pic one is the actual patch. Pic 2 is a test area I did just covering a dent.

Thoughts?

Brandon

1timduke · « **Reply #1 on:** July 09, 2009, 07:43:24 PM »

If you know a plumber, get one of his inflatable pipe plugs, or go to Home Depot, buy, use, and return

They blow up with a regular tire pump and hold fast. Should be easy to find one to fit the filler hole.

-Tim

manjisann · « **Reply #2 on:** July 10, 2009, 03:57:10 AM »

Bumpity,

Any other thoughts guys?

Brandon

razor02097 · « **Reply #3 on:** July 10, 2009, 04:27:49 AM »

If you go with the air...don't fill it with more then a few psi... You would be surprised how much damage 5 or 10 PSI can do.

You can always fill with water, dry the outside and see if there is leakage

bryanj · « **Reply #4 on:** July 10, 2009, 04:33:27 AM »

Plug all the holes that are supposed to be there and hold it under clean water to see if bubbles appear----and i aint talking Jacksons monkey here

nokrome · « **Reply #5 on:** July 10, 2009, 06:09:58 AM »

i used an expanding rubber type freeze plug to fill my filler hole
if you decide to use air be very careful not to use too much pressure, im not sure about it exploding but i know that more than a few psi will cause the tank to start to spread apart and you will not be able to squeeze it back into place without creasing it. (dont ask me how i know)

mystic_1 · « **Reply #6 on:** July 10, 2009, 06:23:42 AM »

Got a vacuum pump?

mystic_1

manjisann · « **Reply #7 on:** July 10, 2009, 06:34:39 AM »

Quote

Got a vacuum pump?

My dad had an AC evac pump, unfortunately I didn't keep ahold of it when he passed. Man I'm regretting not holding onto some of those tools!

Quote

i used an expanding rubber type freeze plug to fill my filler hole

The only issue is the hole isn't perfectly round, it has a small square for the locking part to go through, so I don't think that would work.

I'm thinking I'll just hook a length of tube up to the petcock nipple and ducktape the filler hole really well and then just blow into the hose. Hopefully that will allow me to create enough pressure to force air out of any pinholes and I'll just put soapy water on the weld area and see if any bubbles appear (not MJ's monkey!) I'm pretty sure I can't overpressurize the tank with just my out of shape lungs

Brandon

Frankencake · « **Reply #8 on:** July 10, 2009, 07:03:10 AM »

I used a large fender washer, a toggle anchor bolt and a piece of silicone rubber sheet. The toggle bolt has to be large enough to span the hole and the washer has to be large enough to make a good seal. An extension on the under water idea is to plug the petcock and hold the tank under water but with the fuel vent open and on the down side. It won't bubble if you don't have a way for water to get in. Just fill it with water to simplify all of this and make sure you dry it with a hair dryer when you are done. Put it in the oven on low with the door open to dry, but only if you live alone

.
Finish your grinding before you do your test. If it has a small pin hole or holes. POR-15 will seal it. Usually, after such an extensive compromise of the skin of a tank, it is a good idea to seal your tank anyway.

Alan F. · « **Reply #9 on:** July 10, 2009, 07:49:43 AM »

Quote from: razor02097 on July 10, 2009, 04:27:49 AM

If you go with the air...don't fill it with more then a few psi... You would be surprised how much damage 5 or 10 PSI can do.

You can always fill with water, dry the outside and see if there is leakage

I'd go with this type of test, but I'd get an air pump like you'd use for a basketball or a football, and a rubber cork type plug from a hardware store.

Poke a tiny through hole in the cork with an ice pick or seal pick or a nail or something for the air pump needle to go through.

Block the tank up on a couple lengths of 2x4, and with the petcock still attached and in the on position (don't want to damage it), put on a short length of fuel line and fold it over and clamp it tight so it doesn't leak.

Fill the tank 75% with water then cork the filler and stick the pump through the cork, only 1/2 stroke on the pump should be plenty for a couple pounds of air.

Watch for leaks or drips, leave it overnight and check again later, just leave it with a pound or so of pressure on top of that water.

Does anyone think this would add any value to the test?
-A

manjisann · « **Reply #10 on:** July 10, 2009, 09:09:14 AM »

Thank you all, I think all these ideas would work. The only issue is I don't have a bike pump.

Is it possible to temporarily use the fuel cap as a plug by blocking the breather with some tape? I know its petty but I'm really trying hard not to buy anything I don't have to, build is way over budget. I may just end up finishing the grinding, put the petcock back on and fill with water overnight and see if any drips occur. Maybe I'll use blue food coloring just to be sure I can see them

Brandon

scartail · « **Reply #11 on:** July 10, 2009, 09:31:38 AM »

Quote from: manjisann on July 10, 2009, 09:09:14 AM

Thank you all, I think all these ideas would work. The only issue is I don't have a bike pump.

Is it possible to temporarily use the fuel cap as a plug by blocking the breather with some tape? I know its petty but I'm really trying hard not to buy anything I don't have to, build is way over budget. I may just end up finishing the grinding, put the petcock back on and fill with water overnight and see if any drips occur. Maybe I'll use blue food coloring just to be sure I can see them

Brandon

Someone in the neighborhood will have a compressor or a pump, or go to the local gas station.

If you aren't to set on your decision, i would suggested using an inner tube. Cut it so you can wrap the filler (keep the stem, so you can blow it up). Use the remaining rubber to cap off all the other orifices. Pump it up, and go over your welds with soapy water.

IHWillys · « **Reply #12 on:** July 10, 2009, 11:36:35 AM »

Your hand can hold a few psi(but not much more) while making room for a nozzle in the crook between thumb and first finger. Swipe the welds with soapy water and look for bubbles. It can be a bit of a trick to somewhat seal the filler with one hand while operating the nozzle with the other all while holding tank looking at the welds but this all costs nothing and has low risk of damaging tank or yourself. Air will get through anything fuel would get through while water won't always do so.

Personally, I'd line it but I understand the desire to not line the tank and to not spend anymore money. If you do go the liner route, check out the Caswell epoxy liner.

Ken

razor02097 · « **Reply #13 on:** July 10, 2009, 11:42:09 AM »

If you have a shop that repairs radiators near you they could probably hook you up with all your testing and sealing needs

Don R · « **Reply #14 on:** July 10, 2009, 01:13:50 PM »

Test with water, rinse out with alcohol to remove water. When I have had to weld on a tank that had gas I used methanol to wash out the gas then water to wash out the methanol. purge with inert gas from your mig or tig and weld away.

manjisann · « **Reply #15 on:** July 10, 2009, 01:25:33 PM »

Quote

Your hand can hold a few psi(but not much more) while making room for a nozzle in the crook between thumb and first finger. Swipe the welds with soapy water and look for bubbles. It can be a bit of a trick to somewhat seal the filler with one hand while operating the nozzle with the other all while holding tank looking at the welds but this all costs nothing and has low risk of damaging tank or yourself. Air will get through anything fuel would get through while water won't always do so.

Personally, I'd line it but I understand the desire to not line the tank and to not spend anymore money. If you do go the liner route, check out the Caswell epoxy liner.

Ken

Ok this is the kind of out of the box thinking I was hoping for! Thank you to all who have replied, all of the things I've read seem as though they would work. I know making a penny pinching person happy isn't fun so thank you again for trying!

The beauty of this idea is I already have all the parts I need, I have a hand to plug the fuel inlet, and should be real easy to find a tube and something to plug the petcock area.

I have a Por15 kit, but since this tank didn't have any sort of liner in it I didn't get the one with the stripper in it. Since I had to buy the parts bike to get a good frame unfortunately I'm running on spare change for the time being, so anything I can do to shave cost without sacrificing safety making the bike look good (sadly that has taken a hit as well

) must be explored.

I will report back with my findings and observations.

Brandon

Alan F. · « **Reply #16 on:** July 10, 2009, 06:59:18 PM »

If you're interested in sealing the filler cap, couldn't you take a few square inches of inner tube material and place it over the filler opening before closing the cap?

Seems like it'd seal nicely for cheap.

manjisann · « **Reply #17 on:** July 10, 2009, 07:00:08 PM »

SUCCESS!!! I had to grind out and reweld one spot a few times to get the stupid pinhole to seal, but she now is leak free!!!

I used duct tape and an old hose I had around, had to hold it down to seal it and it wasn't completely sealed but well enough that it forced air out of the pinholes. I can also now light my breath on fire

Thanks all for the awesome suggestions!!

Brandon

Industrial Cafe · « **Reply #18 on:** July 10, 2009, 07:06:47 PM »

I use starting fluid for everything, it's cheap and evaporates completely, shoot a ton of it in and it'll weap out of any leaking areas.

a rag wrapped around your blower tip on the air compressor will do the trick without blowing up your tank.

no air compressor? use your shop vac in reverse with a rag over the hose to seal the mouth and stop #$%* from blowing into the tank.

no shop vac or air compressor? go buy a shop vac or an air compressor and read this post again.

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Author Topic: Welded up my tank, how do I test for fuel leaks?? (Read 3608 times)