Petrol Tank woes

[jhg1958]

Towards the end of last summer I started to notice a smell petrol around the bike that only got worse.  Now I am getting petrol drips from the back LHS of the tank.  I was unable to see the source although there was a bit of bubbling of the paint.  So I bought a cheap endoscope from fleabay I must admit it works a treat.

Unfortunately I still cannot see any leak however I can see a lot of corrosion that looks very uneven probably due to condensation.

I have read on this forum about cleaning the inside of the tank with nuts and bolts or even gravel. I am worried about making any pinholes worse.  Any advice would be welcome.

As an alternative I am tempted to use “Evaporust” to remove the rust before POR15 tank sealer. I took this from motorcycle forum https://www.motorcycleforum.com/threads/por-15-gas-tank-restoration-kit-how-to-tips.199570/

First job is to get some plugs for the tap holes I think they are 3/8” BSP thread. Then buy the rust remover.

I was wondering how to seal the filler cap the only way I can see is to put some plastic under the filler cap.

See the pictures of the inside of the tank.

I was lucky.  When I removed the tank found that it was rubbing on the oil feed to the rocker box!  I am not sure how much damage might have been caused before I noticed the oil. See photo.

John

[trevinoz]

To seal the cap hole make a bung out of thick rubber.

[limeyrob]

Try golf tees, they are very handy for all sorts of things.

[CheeserBeezer]

My method for checking tanks is a s follows. Flush the tank out with soapy water, then sit it on a radiator until dry. Fit both taps and attach a fairly long piece of tubing to one of the taps which should be left open. Close the other tap. Fit the petrol cap down tightly using an oil filter wrench, then just block the breather hole in the cap with some tape. Paint the suspect area of the tank with soapy water. Blow into the tank down the long pipe on the open tap. That's all the pressure you need and you'll see bubbles in the soapy water where the holes are.

[Rex]

Indeed, never ever do as some Net sages say to do and connect a compressor-driven airline, as it'll blow a seam.
Likewise the old tripe about blowing dents out with an airline is a nonsense too.

[limeyrob]

I trained on aircraft and of course wing tanks get leaks so they use soapy water. We were shown a safety video from Boeing - a B707 with the whole top wing skin pealed off. took about 1/2 psi.  The procedure was to use a 2" dia manometer so if it over pressured the water blew out, but someone had an idea to save time.....
They then changed to having a "volunteer" climb inside, put a perspex hatch on and pull a slight vacuum while the "volunteer" crawled about in a 18" space with a torch, a jar of soapy water and paint brush while inhaling kerosene fumes.

[berger]

a compressor driven airline found my leak on the coffin tank, just regulate the pressure you don't have it on full pressure.

[jhg1958]

Stupidly I decided to tackle relining my petrol tank before Christmas in the recent warm weather.  The tank was not desperately rusty but I wanted to cure the leak.  I had already drained and removed the tank and I has received two 5/8” BSP plugs for the tap holes and a rubber bung for the filler hole. If anyone needs a bung for the filling hole let me know as I have 2.

I taped up large parts of the paintwork so I would not spoil it. And poured one 1l of evapo-Rust into the tank, shaking and turning the tank so all surfaces were covered by the liquid.  After 24 hours (as per instructions) I emptied the tank and looked inside.  Not much of the rust had been removed.  I should have realised the speed of chemical reactions, in this case rust removing, is proportionate to the temperature.  It doubles with every 10C. Although it was a warm winters day it was only 11C in my unheated garage. In summer you should expect 20C so this may take a little longer.  One more day of turning and shaking.  This time the solution came out black suggesting it had done all it could.

I washed out the tank with boiled water as boiled water has less dissolved oxygen that causes flash corrosion. As I shook the tank with hot water it began to pressurise.  Now I found  out where the leak in the tank was.  It was around a repair at the back of the tank. It was by an old brazed repair and was not there before I had the tank painted. I suspect it was caused by the tank rubbing on the frame.  I have 2 rubber mats on the frame but rear one had compress letting the tank touch the frame.

Finally I rinsed it out with meths and dried with a hair drier for about 2 hours.

Today the temperature has dropped and too cold to work so I decided to preserve the tank and leave the job until spring.  I put about a pint of oil and paraffin gave it a good shake to cover all the surfaces and sealed it up.     

John

[chaterlea25]

Hi All,
Some words of warning about "Evaporust"
If a part of the object you are de rusting sits above the level of the liquid (in the air)
In spite of dunking all said part in the solution severe erosion of the object will happen at the line where liquid and air meet..
This happened to a part I was treating, I had left it part submerged for a day or two..

I would be fearful of letting a fuel tank part filled with evaporust sit for any length of time
Filling a four gallon tank with Evaporust would be fairly expensive ..

I have a vintage BSA flat tank to de rust very soon, once I remove the failed lining that's in side it. I have 2 containers of evaporust  that should be enough to fill it completely

John

[sean]

go to your local wine kit store they sell different size rubber stoppers for wine carboys and will have one that will fit in the filler hole
drill a suitable size hole to push a soccer ball air pump needles [ amazon] just use a bicycle pump you only need a small amount of air 1 or 2 psi ...put the tank in the laundry tub full of water and you will see the bubbles from the leak
regular white vinegar is what I use to eat the rust  but it takes a week or so
if you have pin holes I would cut the weak part of the tank out and braze in a new piece , hopefully its on the bottom where it wont show .
lots of different methods to make brazing gas tanks safer due to fumes on u tube .
good luck

[jhg1958]

John

I know I did not have enough evaporust but you say it would be very expensive to fill the whole tank with it.  My tank is not dreadful but I was worried about any rust at the bottom before I lined the tank with por 15.

I do not plan to braize the tank but to line it.

John

[sean]

John

I know I did not have enough evaporust but you say it would be very expensive to fill the whole tank with it.  My tank is not dreadful but I was worried about any rust at the bottom before I lined the tank with por

I do not plan to braize the tank but to line it.

John

If you plan on lining the tank follow instructions to a “T “ prep and temps are very important to a successful outcome.
Over the years I have had the best luck with Caswell 2 part tank liner over… did BMW 5 yrs ago still like new no sign of failure.

[Rex]

To seal the cap hole make a bung out of thick rubber.

Or cut a valve + 4" circle out of an old inner tube and secure with a Jubilee clip. You can maintain a steady (and very low!) pressure then.