Problem with leaking tank and wrong mounting

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Problem with leaking tank and wrong mounting

Postby schrottschlecker » Tue Jan 12, 2021 7:43 pm

Hello there,
I have bought a tank for my AJS on ebay. Unfortunately, the tank is leaking. I guess the reason is “classic” and a weak point for these motorbikes. Someone has tightened the mounting bolt so hard that it drilled a hole in the tank bottom. You can see it by looking into the opening. To try to fix this, some dabbler has brazed nuts and studs into the plates that are welded to tank bottom. Still leaking on 1 side.
I would like to keep the paint of the tank as is. What would you recommend to do? Cut-off the plate with the stud, weld the hole and reweld new plates with correct thread? Leave the side with stud which is tight untouched?
I am curious what you would do.

Thanks for your advice.

Cheers,

Christian
tank.jpg

tankstuds.jpg

tankhole.jpg
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Re: Problem with leaking tank and wrong mounting

Postby Duncan » Tue Jan 12, 2021 7:53 pm

Hi Christian, you might wish to try fitting the tank first to help you decide, having fixed studs does make things more challenging.

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Re: Problem with leaking tank and wrong mounting

Postby g80csp11 » Tue Jan 12, 2021 8:01 pm

I believe that you cannot weld successfully over a braze unless you completely remove the brazed filler material before you weld. Brazing filler metals, such as copper, have a low melting point and will melt or crack from a high-temperature welding electrode although a brazed patch should still be ok to repair the tank .
It may be that cutting out a repairing back to standard is the real solution

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Re: Problem with leaking tank and wrong mounting

Postby schrottschlecker » Wed Jan 13, 2021 7:40 am

Duncan wrote:Hi Christian, you might wish to try fitting the tank first to help you decide, having fixed studs does make things more challenging.

Hi Duncan,
that is correct. It would only fit if I would take off the handlebar bracket first. That would be a compromise and ok for me, rather than risking that the tank gets damaged by removing the stud.

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Re: Problem with leaking tank and wrong mounting

Postby clive » Wed Jan 13, 2021 9:28 am

If you are happy to leave the studs they look a bit long and reducing them to the minimum length required with the rubbers and nut in place (and perhaps room for a drilled hole and split pin) might make it easier to get the tank on and off.
To cure a similar leak on an autojumble purchase for me a friend welded either side of the plate and then drilled the plate and fitted a "top hat" with the correct internal thread. As you already have the stud brazed in place and assuming the leak is not running down stud then you could simply weld either side of the plate. This requires much greater welding skills than I possess but it's a relatively easy job for a skilled welder.
If you decide to pressure test the tank, brace across the mounting points with a plate or even at relatively low pressures the tank will spread and the studs will no longer fit in the frame slots!
clive
if it ain't broke don't fix

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Re: Problem with leaking tank and wrong mounting

Postby schrottschlecker » Tue Jan 19, 2021 10:09 am

clive wrote:If you are happy to leave the studs they look a bit long and reducing them to the minimum length required with the rubbers and nut in place (and perhaps room for a drilled hole and split pin) might make it easier to get the tank on and off.
To cure a similar leak on an autojumble purchase for me a friend welded either side of the plate and then drilled the plate and fitted a "top hat" with the correct internal thread. As you already have the stud brazed in place and assuming the leak is not running down stud then you could simply weld either side of the plate. This requires much greater welding skills than I possess but it's a relatively easy job for a skilled welder.
If you decide to pressure test the tank, brace across the mounting points with a plate or even at relatively low pressures the tank will spread and the studs will no longer fit in the frame slots!


Hi Clive,
in case I will leave 1 stud, assuming it it is tight, I will shorten it to a maximum. For the leaking side, I will create a plate with the correct thread. What do you mean with "top hat"? Like an insert?

Regards,

Christian

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Re: Problem with leaking tank and wrong mounting

Postby SPRIDDLER » Tue Jan 19, 2021 12:29 pm

schrottschlecker wrote: What do you mean with "top hat"? Like an insert?



Yes, something like this......

Top hat insert.JPG


https://www.ebay.co.uk/itm/8mm-RIVNUT-W ... 1095229500
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Re: Problem with leaking tank and wrong mounting

Postby clive » Tue Jan 19, 2021 5:36 pm

Thats it Sprids. means you cannot repeat the damage
clive
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Re: Problem with leaking tank and wrong mounting

Postby Mick D » Tue Jan 19, 2021 6:02 pm

clive wrote:means you cannot repeat the damage


Hi

Standard rivnuts such as that are 'open', ie a bolt can be threaded all the way through, and thus, repeat the damage. Closed rivnuts are available and usually specified as such.

Regards Mick

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Re: Problem with leaking tank and wrong mounting

Postby clive » Tue Jan 19, 2021 6:41 pm

Yes a top hat with the top still on the hat :?
clive
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