How to seal leaking fuel tank fittings

[JerzyGeorge]

Good Dy All

 

My Savannah developed fuel leak from fuel yank fittings

 

It does not leak from loose rubber hoses

 

It leaks from bad seal between fuel tanks wall and hose fittings.

 

What is the best way of fixing it ???

 

I pull;ed off the wing skins from under the tanks already but need to find the reliable way to seal it

 

I would appreciate any suggestions

 

George

 

 

[Kyle Communications]

welcome to the club...its a issue as the way they do the connection to the tank is crappy. I have dealt with this several times and the best solution so far is my latest fix. It seems to work great but unless you have access to a lathe I havent seen any fittings around like it.

 

I have posted some pics in my blog about it bit with all the tank leak issues I have had...but mainly with 1 tank which I stuffed up when I initially fitted the first fitting and found out the traps. I will see if I can find them and post them here

 

 

[Kyle Communications]

This shows my latest fitting...it works a treat...and so it should

 

Another NEW Savannah XL on its way

 

 

[Kyle Communications]

This is from way back when I first got the plane flying page 29 and 30

 

Another NEW Savannah XL on its way

 

 

[IBob]

Hi JG. Did you try tightening the fitting? I did mine using a wrench and multi-grips at the thread end as per the pic here:

 

Savannah S Build Notes - Fuel Tanks

 

This allows the fittings to be snugged up well, though with care, as they are aluminium.

 

I'm told the principal reason for leaks is plastic swarf from the drilling, so if tightening doesn't work you may have to take the fitting out and try and see or feel the inner hole face.

 

For my build, I worked up through drill sizes, and put the last drill through by hand. I think this gives the best chance of cutting a clean hole. I then 'felt' round the inner hole face with a wire hook, looking for swarf. I did all this after running some test drills through a plastic barrel, and observing that putting a big drill through a small hole sometimes dragged the drill in and made an ugly hole.

 

I'm really hoping I've got it right, as I can see how awkward it will be once the tanks are in!

 

 

[IBob]

I also think there is a problem or error with the instructions, which call for the larger 12mm fitting to be put through an 11mm hole in the tank.

 

The only way to do this is to wind it through, which cuts a (useless) thread in the clean plastic hole you just drilled, and risks raising plastic swarf round the inner edge. Which is exactly what you don't want.

 

Then, when you tighten the nut on the fitting, this useless thread you just cut is actually preventing the inner flange of the fitting from being pulled hard against the inner face of the tank: unless you pull the nut up tight while further turning the fitting. But how much to turn it?

 

I wonder if the hole was 12mm, and we were also warned to drill and check the holes very carefully for swarf, whether there would still be the fuel leak problems that Mark reports.

 

Does anyone else have thoughts on this???

 

 

[eightyknots]

I also think there is a problem or error with the instructions, which call for the larger 12mm fitting to be put through an 11mm hole in the tank.The only way to do this is to wind it through, which cuts a (useless) thread in the clean plastic hole you just drilled, and risks raising plastic swarf round the inner edge. Which is exactly what you don't want.

 

Then, when you tighten the nut on the fitting, this useless thread you just cut is actually preventing the inner flange of the fitting from being pulled hard against the inner face of the tank: unless you pull the nut up tight while further turning the fitting. But how much to turn it?

 

I wonder if the hole was 12mm, and we were also warned to drill and check the holes very carefully for swarf, whether there would still be the fuel leak problems that Mark reports.

 

Does anyone else have thoughts on this???

Undersized holes like you describe make for an 'interference fit' (this is how a self tapping screw or coach bolt works) but this works against the 'clamping fit' that is desired in the fuel tank. Your explanation sounds pretty reasonable and it seems very likely that this is the root cause of the troubles people are having.

 

 

[Groundhog]

Looks like to tanks are rotomoulded so there will be uneven thickness on the internal surface of the tank, as much as 2-3mm, so using a metal fitting it will leak as it doesnt have a flat surface to work against. If all else fails you can use a SPIN WELD fitting which can give you a chance of salvaging the tank, then use a metal hose barb fitting to connect your hose to.

 

 

[Kyle Communications]

I didnt know that was available Groundhog...what a fabulous fix for the Sav tanks...if I have any further trouble I will be sourcing these. Makes life a lot easier to be able to fit a spinweld then you have a screw in fitting

 

 

 

[Kyle Communications]

Infact I am seriously considering do this for Mabels tanks when I get to it

 

 

[Groundhog]

There are spinweld with brass insert threads so you reduce the possibility of cross threading the fitting. You also need to clean the weld area with acetone or metho. There is also a SLIP or friction reducing agent you apply for better bonding. Also helps with cleanning up.

 

 

[rankamateur]

I Spin Welded the whole air frame for my first build ( When I was 9 years old), The skins were riveted on with Spin Weld rivets too. There was also a helicopter kit available at the same time as well.

 

 

Don't worry about watching the video but the tool she is holding is the same one kids were using in the 70's to build airframes. Be completely out of the question these days due to safety concerns I am sure. Wouldn't want any little kiddies developing an interest in building things that fly, would we?

 

 

[Kyle Communications]

I see there is a company here in Brisbane that has them supposedly although I couldnt find them on their website. Where do you get them from?

 

 

[Kyle Communications]

I am also thinking the bigger spinweld fittings could be fitted to the filler of the tanks then just make flush fitting screw caps for the tank fuel caps. Just cut the thread off the fuel tanks and fit the spinweld

 

 

[Groundhog]

When I had our bisiness we could do up to 4 inch (100 mm) but needed a big router with plenty of torque. Might still have some fitting in the junk I kept. Let me know and I will find out where I bought them.

 

 

[Kyle Communications]

Groundhog if you could find out where you got them from that would be great thanks. Do you still have the tools to insert them?

 

 

[Groundhog]

What sizes were you after, need brass inserts??

 

 

[Nobags]

Nerdy glasses Aunty! LOL

 

 

[Kyle Communications]

I dont know I will have to research I suppose as this has caught me off guard. The std outlet hole in a sav tank I think is 12mm and I have one of mine at 14mm so the insert would need to be around those sizes. The top filler hole in the tank I will measure shortly