ok guys spent a few hours cleanig up my 850 gas tank ( lefty) , only to discover it has a pin hole in it.Can it be repaired and if so what would be best way, ie. brass weld, lead fill, solder,. There has not been fuel in this tank for at least a year all washed out. De rusted inside and out. This is a hole smaller than a pin head any suggestions !!! NOOB....

Yes it can be repaired by pouring in an epoxy which is sold to seal and repair rusty bike and car fuel tanks.
I just repaired a rusty right hand tank and it works a treat.
Where are you as I have enough left over to do another tank

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Take it to a radiator place.

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Dean Hutton's first car was a Mini.

The epoxy forms a protective coating over the rusty bits, basically like a membrane inside the metal fuel tank

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Check out this product.

www.por15.com/

I have used it for two mini tanks, one becase it was a right hand tank with rust issues - worked a treat.

But I suspect a second hand tank would be a better / cheaper option, unless you are after an original 850 one.

One pinhole in a 40 year old tank could be an indication of a wider problem! Maybe get it opened and treated correctly or get another

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"Show me the Mini!"

Stick a pin in it.

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Respect mine and I'll respect yours.

A word of warning on fuel tank sealer. Mk1 Mini's (and possibly later models) have a screen on the fuel pick-up pipe and sealer will likely block it or partly block it. It might be a good idea to remove the screen before you seal but this will mean cutting a hole in the bottom of the tank.

Al

Good point regarding the screens.
You may be able to pry them of through the filler hole or gauge hole.
My Cooper S tank, and clubman tank had the screens, which I removed.
The Por15 is designed for general rust and small holes.

find another tank...

When I did the RH tank a while back I stuck a drill up the outlet pipe afterwards. My pump has an intake screen anyway.
Beware, this stuff can also block the little air vent pipe at the top of tank. Stick a little drill in it too to ensure it's clear.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

When you've finished sealing the tank, a shot of compressed air in the various holes should clear them but the screen is very fine and does not completely clear easily.

Al

Same as what Doc said, I blew air through the outlet in my tank but it still sealed the mesh so I pushed through the mesh with a rod and now run an external fuel filter just under the floor. And yes the vent at the top of the tank is small and also needs to be cleaned out. But the inside of the rusty tank is all nice and smooth with an epoxy coating.

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

When your gas tank pressurises your repair may fail? ... a gas tank is a pressurised vessel and will need proper testing before its put back into proper use..


...

..

Unless of course you mean fuel tank.

I would think about getting another tank. They are easy enough to get new or a second hand one in good nick. When it comes to fuel the less contaminated the better it is for the engine and performance. Just get one from a later model mini to be sure.

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1975 1310cc Street Mini Custom
1974 Leyland Mini daily driver
2008 Cooper S R55 Clubman