Are joins on 1970 911 petrol tanks brazed & how seal seams?

[RobFrost]

I'm about to attempt to pressure test my petrol tank for leaks. If it's leaking, I'm expecting the seams to be the most likely problem area. But looking ahead to any repair, are the seams brazed? This seems the most likely method used to achieve a watertight seam and I know from gas welding in the past it can cause a lot of spitting when welding nearby. What methods are there of re-sealing corroded seams?

[Barry]

No, they are roll-welded.

If it's leaking from the seam it would be very hard to repair as a) the roll weld is back from the very edge of the two joining flanges, b) any repair is unlikely to fully penetrate sideways enough into the seam, and c) If you attempted a brazed repair in this area, you'd never be able to remove all of the flux (even assuming you'd managed to get the metal clean enough in the first place.

A repair on the single pressed areas might be possible with brazing (I have done this) because you can inspect it and make sure all flux has been removed.

Even so, you're probably best off considering one of the resin-based solutions that seem to work O.K.

[RobFrost]

No, they are roll-welded.

If it's leaking from the seam it would be very hard to repair as a) the roll weld is back from the very edge of the two joining flanges, b) any repair is unlikely to fully penetrate sideways enough into the seam

Thanks for the tip. In that case if it needs a weld to the seam perhaps I'll try making perpendicular cuts into the tank at either end and weld those closed too.

[Barry]

Yes, you'd want to grind right back into the seam and well beyond (e.g. left and right of) the corrosion.

Even so I'd recommend not getting into welding at all and trying the resin-based solutions.

If you were to braze or weld, don't under estimate just how hard it is to purge the tank of vapour. I've accidentally blown up a 1915 flat tanker tank (fortunately saveable) after being a bit casual about vapours. It was particularly unpleasant I can tell you. After that, the attraction of a resin solution was all the more real.

[jb]

I admire your bravery but maybe consider a new tank?
Not huge money to save all the heart ache
https://type911shop.co.uk/epages/de867c ... ducts/3781

[RobFrost]

I admire your bravery but maybe consider a new tank?
Not huge money to save all the heart ache
https://type911shop.co.uk/epages/de867c ... ducts/3781

It's not the money. Each replacement part erodes the magic. Also, the quality of this tank is amazing. Everything I work on on this car, the quality surprises me.

Sent from my SM-G988B using Tapatalk

[RobFrost]

If you were to braze or weld, don't under estimate just how hard it is to purge the tank of vapour.

One of the things I was mindful of, is it's not necessarily the petrol fumes. If welding vapourises oil, resin or paint into smoke, that's highly explosive too. For now the tank's going back in without resin or welding as it passed the pressure test. Hopefully I tested it accurately. It doesn't look punctured - but there was runny/tacky bitumen in the base of the boot around the seams and a strong smell of petrol so I thought petrol could be dissolving something.