How to repair a dent in alu tank?

put the cap in and blow straight into one petrol tap hole with the other closed. build up the pressure using the guage on the compressor. aluminium will pop out anywhere and everyth==where but if it's a wide dink on a flat surface it will be the first place to pop. if it's a dent on a corner well then you've had it! use rods of different shapes for this. remember the old car jack handles in your spare wheel kit? that awkward shape? ideal!

regards

Taffy

I dont know about heat and pressure in this application, because of the aluminium, you could end up with a big hole melted where the dent is verry easily.

Maybe wait for some other ideas her, because there are a few guys who use aulminium tanks, but i would suggest filling it with water, with the petcock turned off or removed and blanked off and the fuel cap on & sealed so it cant de pressurise, then pit it in the freezer, as the ice crystals form, the expansion should push the dent out.

of course you may end up with a bit of extra fuel capacity in the tank afterwards, and worst case if the welds are poor, you may end up with a split, but that can be re-welded.

the water / freeze method is meant to be verry effective in re-forming 2st expansion chambers.

Azza.

heat? i never said 'heat' azza?

i've done this many times in 14 seasons of roadracing. i got a 20ltr tank to 22ltr with just this method.

if you actually think it'll explode under pressure of an air jet? well......!

as i've said before, stick the mouth over the exhaust pipe of a car for 10 minutes with all vents open.

regards

Taffy

I'd try a cross between the two suggestions. If you fill it with water then pressurise it gradually with more water from a small hand pump you will have infinitely more control of how much it expands and where. When it starts to move you can drop the pressure off much more quickly too. Water is a few thousand times less compressible than air at room temperature.

The other thing you could try is to butt up a large hose over the dent then get the ideal girlfriend to suck the dent out! :wink:

what experience have you got of this then brad? it's alright sitting as judge in the middle swaying decisions but i want to know on what experience it is based to make this informed decision?

regards

Taffy

Ha ha ha farking mellow out Taff, you beat me to making the post, which means i wasnt responding to you or challenging you, i'm a slow typer okay! especially when im meant to be working!!

Hannu mentioned heat and air pressure, which, to me has red flags waiving when talking 'bout aluminium.

water is a little easier and safer to work with, even if you 9/10ths fill the tank so there is an air gap to help compensate (and it doesent work) you can have another go, do it with heat, and blow it, then you have a serious patch job on yer hands.

no dis respect intended maestro

Azza.

brad's a big boy now and answers to the name of azza! :twisted: :twisted:

regards

Taffy

how thick are these tanks ?

im making one soon, just wondered what they do re aluminum thickness

regards
Bushie

bushmechanic said:

how thick are these tanks ?

regards
Bushie

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what are we testing their IQ now as well? :twisted: :twisted:

hannu, you must have overdone it fella. and to rupture a weld well what can i say! sorry but i'm sat here pissing myself with laughter! :lol: :lol:

i did say to build the pressure at the gauge....

regards

Taffy

Bushie, I checked one out (not an Omero tank) at the force ride in '08 on one of Orangeberg' crew's bikes, and i'd say it would be lucky to be 1.8mm alu.

have you got a pattern sorted for making one? i was toying with the idea of making one or some propotypes, but the mig my wife got me only does gassless, and i havent got three phase in my shed, so unless i spend countless hours at night down on my old man's tig, i guess its not happening!

Hannu, get it re-welded then have another go with water and put it in a freezer.

Azza.

Hey Taff. You going for the record for the greatest number of people you can piss off in the one thread?

My experience? When you find the ideal girlfriend, marry her like I did!

Be happy to answer to the name Azza. Have always found him polite & personable. Not sure I'd be happy with anyone calling me Taff at the moment though.....

ALWAYS BE EXTREMELY CAREFUL WHEN APPLYING HEAT TO A FUEL TANK. BE DOUBLY CAREFUL IF YOU TRY TO WELD IT!!!

This is where I'd definitely recommend filling with water. Of course you can't have the water in contact with the other side of the area you are trying to repair as it will suck the heat away. Certainly fill it so that you have the minimum free space just underneath the area you are heating. It is easier than you think to blow youself up if you ignite an "empty" tank full of vapour. A previous next-door-neighbour's brother died in this manner.

Taffy said:

...it's alright sitting as judge in the middle swaying decisions...

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Sorry if filling it with water to pressurise it is too close to Azza's suggestion for your liking.

Maybe this is more palatable:
If you fill it with petrol then pressurise it gradually with more petrol from a small hand pump you will have infinitely more control of how much it expands and where. When it starts to move you can drop the pressure off much more quickly too. Petrol is a few thousand times less compressible than air at room temperature.

Experience is in pressure testing lots of things and bending at least one tank. If you have the option, always use the least compressible medium available. Having it not flammable is a bonus.

Have pumped up at least one steel motorcycle tank before in an attempt to remove dents. Your typical tank that wraps over the top rail of the frame tries to straighten out like a bourden tube in a gauge at fairly low pressure. If you keep going the inner skin gets over stressed in tension and yields. A steel tank tends to bend and want to flatten out wider. In my case I was lucky because I could squeeze it back together to fit back on the mounts. If it gets away on you because you can't drop the pressure off when you need to it would soon be fuct.

I would expect a fabricated aluminium tank would attempt to either bend or tear along the welds on the underside.

All the same, you have done it countless times and never had a problem. That is pretty hard to argue against......

have you got a pattern sorted for making one? i was toying with the idea of making one or some propotype

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not yet I want to put it down around the shock and area where teh starter and battery used to be, ally or carbon havent decided yet, then can make a whacking great air box under a new longer flatter seat. and maybe a lighter frame...

ahh sod it I should just get a yz250f with no motor and put the 628 in it. at 26kg on the scales its not a heavy engine but the rest of the berg sure is.

FWIW re welding tanks i use a degreaser called floorprep from phoenix paints http://www.phoenixpaints.com.au/ to get all the fuel residue out and then test with a ligted rag on a string before welding

regards
Bushie

bushmechanic said:

..then test with a ligted rag on a string before welding...

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If I was religious I'd pray you never get a truly positive test.

BundyBear said:

bushmechanic said:

..then test with a ligted rag on a string before welding...

Click to expand...

If I was religious I'd pray you never get a truly positive test.

Click to expand...

Health and safety .... !? Whats health and safety !!

This reminds me of a video i once saw in youtube, some guy put a 2 stroke expansion pipe in the freezer overnight with a little water in it. It worked a treat

i tried searching "freezer" and "dent" but only came up with this lol

http://www.youtube.com/watch?v=gOZ6zyly-lA

Good point Hannu. My apologies to all for getting involved in the crap.

I still stand behind my comments about safety when working on empty fuel tanks though.

Brad W.