Oil tank leak test?

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1974 850 - I've messed with the oil tank before - took it to a blacksmith. He fixed the top mounts and supposedly "reinforced" the bottom one, although it still looks a little weak to me. If I were a smart person, I would've skipped the bottom mount altogether like the CNW refurb. But alas, I am not that person.

Anyway, a few thousand miles and an oil change later, the annoying leak reappeared and I've traced it back to the oil tank. I have the tank off now, but nothing is obvious. What's the best way to test these tanks for a very small leak? I suspect that bottom mount, but if I can at least rule that out I have some other ideas...

Appreciate any advice.
 
Its a bit of a tricky thing to set up but works well. You need access to compressed air. Stop up all the oil pipes, drain hole and oil banjo hole. Rubber bungs or trimmed soft wood plugs works OK. Leave the top breather pipe free. Coat the entire outside of the tank with a rich mix of dish detergent and warm water. Insert the nozzle of the compressed air into the top breather pipe and apply gentle pressure. Air escaping from a crack will immediately cause bubbles to froth. Stop and start the air pressure to see that bubbles appear consistently. Hot oil will find its way out of the tiniest crack. Scrap back any paint around the area and repeat just to be sure.

Mick
 
Another way. Cap off or tape up all openings except the filler neck really well. Put it in the sink full of warm soapy water and put your mouth over the filler neck and blow. Look for bubbles. Probably the bottom mount has some cracks.

Russ
 
Not aware of any "leak test". But am very aware of the fact that the bottom mounting threaded insert is brazed into the steel ,this can develop hairline fractures that weep out a little oil until it separates and gushes oil ,of course only when driving on the Interstate or some fast situation. You can leave out the bolt entirely or have it rebrazed or fit a thick foam rest pad or a bigger softer rubber grommet or cut out the whole bottom and weld in a thicker steel plate or order the true fix from CNW. Do not drive the vehicle the way it is.
 
Thanks All - - - Mick, your test ended up revealing a TINY bubble right where it "looked" like it should be at a scant spot in that bottom weld. Thanks to a kind soul here I now have a spare tank that I can use while the other is tinkered with and/or fixed. I think I'm going to do some more welding at that spot to shore it up - then leave the bottom mounting screw out of the equation. It was a very slight leak, but it makes sense that it reappeared with new oil...

On a side note, I had an exciting time when the rubber stopper plugging up the large hole on the tank shot across the shop at high speed. Glad I didn't have it pointed at my eyeball. I am certainly clueless sometimes.
 
Listen to the voices of experiance, send it to Matt @ CNW or replicate something like what he does. The bottom needs a caver plate to get rid of any micro cracks & then just put a rubber pad under it. Reinforce the top ones & pray!
 
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