AJS & Matchless Owners Club

I have a leak in the petrol tank but it only seems to appear when nearly full, I have removed the tank expecting to find some problem on the inner channel however this seems perfectly o.k there is no evidence of any leak or corrosion, bit stumped now, so can anyone suggest how I can locate the position of the leak, what fluid would be the best to identify the seepage? kind regards

Hi

The best fluid to locate the leak is the petrol itself and my initial suspicion is that the central seam has cracked, (assuming you have one).

If you can't actually see any fluid try getting your nose close and smelling for fuel - this will zero you in to the general area.

Once you've decided where the smell is strongest dust the area with talc or fullers earth - this will absorb any fuel and discolour slightly indicating exactly where the leak is.

Regards Mick

You must have seen fuel leaking and approx. where. As you said when nearly full, but upon testing, the leak never showed up. Was this leak seen after riding the bike? If so could it be the cap leaking. It is quite common to get some leak with a full tank from the cap. If it does leak from this area, just don't fill it so full. Another thought, perhaps you may need to give the tank " time " for the leak to show up.
Just noticed Micks reply come in, the test he suggests would also need a little time to show petrol seeping out.

GOLDSTAR wrote:I have a leak in the petrol tank but it only seems to appear when nearly full, I have removed the tank expecting to find some problem on the inner channel however this seems perfectly o.k there is no evidence of any leak or corrosion, bit stumped now, so can anyone suggest how I can locate the position of the leak, what fluid would be the best to identify the seepage? kind regards

Hi Richard

I have just located and fixed a leak in my Ariel VH tank. I drained it out and pressurized it with a footpump through the fuel tap with the tank cap on with some tape over the cap breather hole. It is important not to put in more than about 4 psi of pressure.
I then brushed a washing up liquid solution over the suspect areas and looked for bubbles.
When I found the leak I cleaned the area thoroughly and not wanting to blow myself up with naked flames I soldered it with a large old fashioned soldering iron which has to be heated with a propane torch. I used Bakers fluid and tinmans solder and just built up a later of solder over the leak.
Still not leaking six months later.

Jim

thanks people, the strange thing is the tank is on a W/ng Ariel, as I said all the inner channel seems perfect, I will have a try at the suggestions, kind regards

Hi

With respect, I wouldn't recommend doing any repair work to the tank until it has been thoroughly vented - sorry if you did this but you didn't say so.

Regards Mick

Hi Mick

Yes I drained my tank and blew the air line through it for ages. When I got round to doing the job a week later I could still smell petrol in the tank so I did it all again. A week later I could still smell petrol so I decided to use a large soldering iron to do the work rather than using a naked flame.

I think it must be very difficult to get all the petrol fumes out to allow welding or brazing to be carried out - not sure how the "professionals" do it. Perhaps washing it with hot water with a hose down the filler neck so the petrol rises to the top and floats out.

Jim

I'm sure I've read (but not checked the science) of running a normal exhaust through the tank, apparently the fumes neutralise the live petrol element. ..... . I can feel somebody about to jump in on this or at least provide a little 'science' (dark, dark stuff).

uktom77 wrote:I'm sure I've read (but not checked the science) of running a normal exhaust through the tank, apparently the fumes neutralise the live petrol element. ..... . I can feel somebody about to jump in on this or at least provide a little 'science' (dark, dark stuff).

Yup seen it done that way. The theory is to fill the tank with inert gas to drive out all the oxygen so the fuel can't burn.

While being all sciencey petrol will find leaks that water cannot go through. Water has surface tension which is why it has a meniscus and forms "beads" on a surface. petrol does neither of these things so will go through smaller holes than water can.

it has been suggested that if I can identify the leaks location then as a temporary repair use araldite to plug it, I will have the tank proffesionaly repaired if necessary but would rather wait until after the Sittingbourne touring week, Latvia and Irish rally, you really would not believe the flakes and damn great lumps of what apperas to be an earlier tank lining I managed to get out of it yesterday, there is still a solid piece that at the moment is defeating me ! . kind regards