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cutting tank open to cure leak.

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Jerry atric View Drop Down
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    Posted: 08 May 2020 at 17:14
Having spent a day trying to get the old Petseal out of the T3 Cali tank, I wonder what the consensus of opinion is on cutting a section out of the underside (after venting etc.) to get at the huge lumps of loose Petseal? The leak appears to be coming from behind the badge. Obviously I can't use a liquid sealant without getting all the old petseal out first as well as the rust. H

Having cut out a large patch, what is the best way of closing the hole back up? I would be using a pro for that bit.

Thanks for any advice.
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Ben. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ben. Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 18:23
Welding or brazing a patch on the bottom of the tank would be tricky, as the patch would tend to separate from the parent metal under heating, and I can´t think of a way to hold them together. MIG welding might allow the patch to be tacked without too much distortion, then welding between the tacks -- I´m not familiar enough with MIG to be sure.
 Soldering with tinman´s solder might work, each surface could be tinned,  then I would probably try with a very hot large old-fashioned copper soldering iron, rather than a flame.
I reckon it would be a risky business, the sort you embark on when all else has failed, but a good old-time plumber would be able to assess your chances of success.
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-HJB- View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote -HJB- Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 19:13
Id imagine cutting and welding will have it’s challenges. How hard are replacements to come by? There’s a chap with a few tanks for sale on ebay at the moment. You would need to figure in paint for either route so it might end up cheaper / easier. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ranton_rambler Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 20:20
I’d say you need someone good with a TIG welder for that.
Ian 
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Ben. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ben. Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 20:38
Bear in mind that any method which melts the metal will be likely to cause differences in the temper of the metal -- if it cools quickly it will become embrittled, and the area will react differently to vibration from the more malleable area around the weld, leading to cracks appearing. Although the tank will be mild steel and unable to be tempered properly, any weld will cool very rapidly, and become brittle.
Soldering was fine for car body panels until cheaper methods arrived.
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Jerry atric View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 21:11
Thanks for the benefit of your knowledge, guys. It doesn't sound like good idea really does it.

If the leak turns out to be one of the badge fixing points, do you have any clever dodges to do a local fix.

The paintwork is very good so I was hoping to preserve it
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 21:12
Soldering rusty mild steel might present a challenge. Fine on clean new metal.
Brian.

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Jerry atric View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 21:25
It seems there is no amateur way around this simple problem. I thought I read that ethanol attacks soft solder so maybe that is not a solution either?

I had a look on eBay. I wonder how the bloke in Bungay came to have so many tanks! They're all described as spares or repair.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote George S Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 21:27
I have used Pro Seal epoxy putty with success Suitable for small leaks. Worth a try for what it cost.
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Ben. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ben. Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 21:44
You´re right Jerry, it seems ethanol attacks brass as well as solder, so brazing is out too.
Seems any kind of surgery would kill the patient.
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 22:32
Are you sure?

Tarnishing with Brass, but no corrosion, and that was over 12 weeks at 45 degrees C, with E20 fuel.
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Ben. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ben. Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 22:41
Nope.
Googled it :- 
Certain materials commonly used with gasoline may be incompatible with high-level ethanol blends, causing them to degrade and contaminate the fuel. Metals that have been shown to degrade over time in the presence of high-level alcohol blends include brass, lead, zinc and lead-based solder.May 22, 2007

Or do they ...?

Your info is more recent, but I don´t know where we would find unbiased advice.

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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2020 at 23:01
Would SAE be biased?
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Jerry atric View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jerry atric Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2020 at 08:18
I had never seen that report, Brian. I wonder if there is bias at that level, we know there's a lot of big money involved in ethanol.

The Pro Seal Putty sounds like it might be worth a go as it is very small weep behind the 'Guzzi' badge so thanks for that, George.

As an aside, the loose sealant in the tank is not gummy as you would expect from ethanol attack, but is in hard lumps so I think it was just badly applied inn the first place, so what is it? maybe someone had a go with fibre glass resin, which I know from experience, doesn't work.
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 09 May 2020 at 08:38
I can find no reference to SAE International, formerly the Society of Automotive Engineers, being involved in the production of fuels.
They have been responsible for setting standards mainly in America, but used globally too.
I can't see how a scientific test which found no corrosion, but considerable tarnishing could be biased.

What I do know is that Ethanol is being used as a scapegoat for problems which were not caused by it. Mainly in corrosion of zinc based alloys, which were actually caused by water and salt, and which also happened long before ethanol was heard of.

However, we digress.

I would say a good TIG welder would be your best option if you go down the cut and repair route.

Years ago (well a lifetime actually) I restored an old BSA which my dad had taken to bits when the big end failed. He had stored the tank outside.
Now chrome was better in those days so it actually looked good, but rattling some pebbles around inside removed a lot of rust.
So I put some petrol in it, and of course it leaked, though somewhere near the top in the frame tube channel.
So I cleaned it carefully and put some Epoxy filler in that area.
It never leaked again in the next 20 years, Bike went to new owner about then so lost touch.
Brian.

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