Author Topic: Petrol Tank Repairs.  (Read 336 times)

Online A10 JWO

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Petrol Tank Repairs.
« on: 08.01. 2020 16:35 »
My painter has examined my dented tank and is quite happy to pull the dent out and respray it. He is used to spraying RGS Tanks and knows his onions. He told me that it will need pressure testing. Has anyone done this as a DIY test or have I got to take it somewhere for this test. I simply forgot to ask him when he examined it. He is playing golf in the sun at the moment and I am just preparing a rebuild. Thanks.

Online Bsareg

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Re: Petrol Tank Repairs.
« Reply #1 on: 08.01. 2020 20:16 »
I've pressure tested a couple of tanks but whether it's the right way I'm not sure but it has shown up small leaks. Seal the filler with polythene, sheet, put hose onto petrol tap and hold onto blowing end of Hoover. Be careful of too much pressure as it's surprising how little pressure is required to cause the tank to "inflate". Spray with soapy water and look for bubbles.
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Re: Petrol Tank Repairs.
« Reply #2 on: 08.01. 2020 20:57 »
If you do need to use an air line then fit the tank strap on the base and put a couple of tie downs round the tank. Use very little pressure, say 3-4lbs.
I have heard of tanks halves flapping out like a butterfly if too much pressure is used.
Then brush a little soapy water over the seams and any suspect areas.

Jim
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Online Bsareg

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Re: Petrol Tank Repairs.
« Reply #3 on: 08.01. 2020 22:03 »
Be carefull, 4 psi = 1/4 ton per square foot !
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Re: Petrol Tank Repairs.
« Reply #4 on: 08.01. 2020 23:07 »
4 PSI is way too much, I have stories about that, as well as dent removal.  There is a readily available tool called a Mity-Vac, should be in ALL your sheds & shops, You can use for both pressure and vacuum testing and very utility-versatile.  I think the chinese have copied them and offer at Harbor freight and other vendors as well.

https://www.harborfreight.com/mityvac-vacuum-pump-39522.html  (This one seems to be suck, no blow, mine does both)

This one, is similar but still not like mine, but mine can easily switch between pressure and vacuum,,

https://www.grainger.com/product/MITYVAC-Automotive-Test-Kit-1XGR6

Simply plug the petrol tap holes and fashion a stopper for the filler neck, I have some rubber ones from laboratory and industrial apps in different sizes and one I drilled/tapped and installed 2 fittings, one for pressure and one for the gauge.  I also have a variety of corks, plugs and threaded and non threaded fittings, and save them as always useful so over the years amassed quite a collection.

I use a rubber maid large storage tub and while soapy water is useful for bubbles, immersing in a 20 gallon tub is better IMHO to spot a pin hole leak.  Traditional radiator shops do this as well when soldering, brazing or welding a radiator or sealed vessel.  If you dont want to bother, see if there is a local shop for a few Pesos $$$ see if they mind testing for you.

NEVER EVER try to use freezing water or Air Pressure to remove dents on a petrol/gas tank.  It will not work out for you, is dangerous and will likely further damage or more likely destroy your tank.

I have a Norton C-Do tank on the wall down in the shop i use as a demonstrator of someone who should know better did so as well.   I one tried it myself and was alarmed at just a few PSI how quickly the sides of the tank splayed out and distorted, needless to say the dent stayed the rest of the tank distended like the belly of the crewman on Sigorney Weavers space ship before the Alien popped out and we all know how that turned out.

So, I got a tank from a guy who, highly educated and skilled in his trade, Industrial Structural engineer (Engineers operate on their own special wavelength).  He too tried the air pressure method and the NotRun tank splayed out like an elephant stepped on it.  I often have used it to illustrate these discussions. I can snap a pix if you like????

The reason is simple,,,a dent ding or distortion in formed sheet metal distresses the metal and its grain structure.  It stretches it and work hardens it as well. That means the dented metal is actually HARDER-STIFFER than the surrounding metal.  Its the LAST thing that will budge.

Pulling dents is a fun & interesting skill and physics lesson in itself... not easily addressed in a short blurb, but happy to discuss, Shrinking, annealing and metal forming alloy or steel as well.
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Re: Petrol Tank Repairs.
« Reply #5 on: 09.01. 2020 00:14 »
My painter has examined my dented tank and is quite happy to pull the dent out and respray it. He is used to spraying RGS Tanks and knows his onions. He told me that it will need pressure testing. Has anyone done this as a DIY test or have I got to take it somewhere for this test. I simply forgot to ask him when he examined it. He is playing golf in the sun at the moment and I am just preparing a rebuild. Thanks.

I just used the standard filler cap, it has a small breather hole but not so much air leaks through that to stop you getting a couple of psi in the tank from an air line, I used a small airbrush compressor in a a sort of “continuous leak” situation, using the main tap as the source of compressed air, and the reserve tap (fully open) and my thumb to control the pressure/leakage.
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Offline Swarfcut

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Re: Petrol Tank Repairs.
« Reply #6 on: 09.01. 2020 11:05 »
    I suppose it depends on whether you want to divide up the various stages of restoration, or just pay the guy for a ready to fit tank.

    It should start with getting the metalwork sorted, dents, rust holes, brackets etc, then a pressure test. As a bespoke service I would expect pressure testing  to be included in the refinishing process, as the initial post indicated that the refinisher would do the dent work. He needs to get the dents out and know to start with, before refinishing, that the tank is OK, sound and does not leak.... not after primer, primer filler, ghost coat, flatting, colour coats and lacquer.  Nor to give you the tank back to check, or worse, you test it when you've paid for the job and got it home.

In the old days it was a ball on a stick thro' the filler cap.....more drastic dents involved chopping out the tank bottom and welding back together. These days we have cheap stick on key and bar puller systems that with skilled use don't even damage the paint (for small, simple dents and creases), and weld on/grind off pins for more serious dent pulling where there is no rear access.

 Tanks are relatively thin and any air pressure needs to be applied with caution as outlined above. Water butt is more convenient than trying to locate air bubbles among soap bubbles.

Your filler cap with a dab of duck tape over the vent hole should seal this area well enough, even good lung pressure, Hoover on blow or a couple of strokes from the good old tyre pump will reveal major problems....by all means have a go yourself, at least you will know before work starts whether there are unknown new problems requiring attention.

Swarfy.


Online A10 JWO

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Re: Petrol Tank Repairs.
« Reply #7 on: 09.01. 2020 16:30 »
Found replies refreshing, spoke to painter at last. He is going to repair the tank and give it back to me for testing prior to paint. Based on the replies I am going to seal the filler and pump air into the tank via the petrol tap. I am going to use an air bed inflation pump or rig up my footpump with an air bed insert.
My painter told me about a flat tank he gave back to the owner for testing. Obviously did not test it and ruined and expensive respray in four colours. Thanks lads.

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Re: Petrol Tank Repairs.
« Reply #8 on: 09.01. 2020 16:44 »
Be carefull, 4 psi = 1/4 ton per square foot !
Hmmmm yeah..... Never really thought of it that way before - it does sound a lot.
I have an old pressure testing pump made for testing pipework which I use which is like an upright stirrup pump with a built in dial pressure gauge. Gaffer tape over the tank cap hole and screw a fitting into the fuel tap hole.
I never went above 4 PSI but perhaps I have dodged a bullet or two in the past. Perhaps I'll keep it down to 1 or 2 PSI in the future.

I have just topped up one of my airgun reservoirs using a diver's airtank. The gun uses a diver's "buddy bottle" which is a standby air tank for emergency use. The working pressure is 232 bar which is around 3364 PSI - imagine the force acting on that. 3364x144= 216 tons per square foot!

"Dangerous" Jim

1959 A10 SR
1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

Too old to Rock and Roll but too young to die  (Jethro Tull 1976)

Offline BSA_54A10

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Re: Petrol Tank Repairs.
« Reply #9 on: 10.01. 2020 09:24 »
On the very few times I have pulled a dent out of a tank i was done like this.
1) fill the entire tank with water the plug off the top as some one else mentioned by glad wrap over the filler hole before you put the cap on.
2) roll the tank so the dent is at the very top
3) apply oxy torch just on the inside of the edge where the dent rolls in
do not be afraid to make it red hot

As the metal heats up the pressure from the not getting quite hot water will slowly roll the dent out.
When the area you are heating is fairly well  in alignment with the rest of the tank move the torch in towards the center and repeat.
Eventually the entire dent will roll out.

method 2 is heat shrinking.
I do not like to use this method as the tank is heated empty and there is always the explosion risk .
Any way it goes like this
1) heat the inner edge of the dent till it is red hot.
Now you have to make a complete circle of roughly the same colour .
Dull red is fine
2 ) splash the red area with a thick water saturated rag,'

As the side of the metal nearest you is contracting the other side is still expanding and will force the dent out.
Same as before you do it one loop at a time.
be carefull not to work too big an area or it will pull flat which is not what you want on a curved surface

The down side of both of these methods is they will leave the repaired section softer than the rest of the tank so if it is the knee region there is a really good chance of putting another dent in there with your knee.

Shrinking works best on flat areas

Should be tons of videos on both methods.
The important thing is not to be greedy and work too big an area at ones and do not be impatient.
It can take a full day or more
Bike Beesa
Trevor

Offline Jules

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Re: Petrol Tank Repairs.
« Reply #10 on: 11.01. 2020 11:41 »
My tank was repaired by working through the filler hole by an old style panel beater, he actually beat the dents out from where the front forks had swung around past the steering stops and collided with the tank - you know the normal crash type dents! He actually metal finished it with no bog and then chromed it, amazing feat.....only problem is he didn't leak test it and neither have I yet, but my plan is to actually use the MiTy vac gun and do it under vacuum by looking for leak down. We used to pressure test fuel systems when building cars in production, but switched to vacuum with leak down check, we found more leaks and were safer....