Bit of a weird question .. what pressure can I take fuel tank to?

[AshimotoK0]

Just finished a customer's computer controlled test machine, which pressure tests automotive components under precise closed-loop pressure control using water up to 160 bar (around 2,300 PSI). I was thinking the other day that if I used the test machine to pressurise a 400/ 4 tank I have, that's quite nice inside but has serious dents in it, it may partially push them out.  Obviously I will need to make adapters, which includes finding the thread size for the petrol tap (won't refer to it as  petcock ... honest Bryan )  and a way of preventing flash rusting inside , when I have finished. Question is, what pressure can I safely take it too without popping it ?

Another hair brained crazy Ashimoto 'experiment' I hear you all mutter and 'Ralph' up there saying "why doesn't he just get on with his fri**in'  bikes'    .... Really miss  his  banter on here.

Ash

[Green1]

I can throw abuse at you if you want Ash 

I'm sure I heard of people filling the tanks up with water and freezing them with mixed results.I know that's how the dirt bike boys push dents out of the expansion chambers.

Mick

[Spitfire]

I heard about this method in the 70's I can remember binning a dented tank from my CB750 just before a friend started using an air compressor to blow out dents, but I cannot remember the pressures involved, what you need is a pressure regulator and a gash tank to find out the limits, I would not think that the pressure would be much.

Cheers

Dennis

[Orcade-Ian]

Hi Ash,
I did this many years ago with air pressure only on a CD 250U tank which had a 'knee' dent in one side.  I used the original cap to seal the neck and made a fitting from brass for the petrol tap (the only petcock I ever saw was at Crufts). As soon as I started to wind up the pressure, the tank wanted to open out like the wings of a bird.  They were not called saddle tanks in the early days for nowt.  Stopped straight away and used padded ratchet straps to prevent that problem and tried again.  Success this time but the dent was not sharp edged.  I would say that the pressure would have been around 50psi tops.

If you are refinishing the tank anyway and only trying to save using loads of filler or get the capacity back to near normal, it's probably easier to try and pry some of the big bits and fill the rest.  I still use UPOL No 1 Smooth and Easy, it's the best I've ever used and never cracks out and can be feathered to nothing.

Ian

[ka-ja]

Hi,
    orcadian is spot on, my nice shiney 400/4 tank looked great after the paint shop, but when I came to fit it, the mounting lugs were wider than the rubber mounts, you need to stop the tank spreading before trying this approach, and it will be very low pressure that does it or not at all!

[mike the bike]

Have you considered cutting a large hole under the tank and knocking the dents out from inside.  Then braze a patch over the hole.

[Trigger]

Air only works on dents ( not crease). I have seen someone do it with a inner tube and a guy once in Bulgaria that had a load of different size air bags. Have seen a guy in the Bristol do it with air and blow the weld on the rim.

[royhall]

I had an RD250 coffin tank done back in the 80s. It got the dent out, but the tank was about 10% bigger when it came back and a lot of the defined shape was gone. That went in the bin. Try the full 2300psi that should shift the dents.

Crikey Ash, its great having you on here. Never a dull moment.

[AshimotoK0]

Cheers for the replies guys. I reckon that looking at the shape of the 400/4 tank it's not worth pressuring it if it's in danger of losing shape. I will try prizing the dents out from the inside.

Cheers ... Ash

[Bryanj]

Not going to jump on the petcock mate, I did this to an XS500 tank I had then had to squeeze it back in (Was a bigger , hefty lad then) then had to solder the front top seam that sprung. After all that can't remember the pressure I used but it wasn't high