Fuel tank boo boo fix

[nichzimmerman]

Good day all,
My main tank's aft hole is out of round thanks to a drop on the floor. Any ideas on the best fix? All I can think of is buy a 3/8" NPT tap and run it through, but I don't like the idea of aluminum shavings in the tank. Thanks in advance. - Nic, #1217

[jim.mclaughlin924]

You might try to turn in a steel npt plug with anti seize grease to straighten it out and clean up with the tap. Turn the tank up so the hole is facing down and the shavings should fall out on the floor.

[svyolo]

It might be too out of round for a tap, but it is worth a try. Boelube does a great job of holding onto shavings when you tap something. It has just the right viscosity to grab onto the shavings.

There are a few other ways to force it back into position, like welding on a rod and using a "slide" hammer to get it back closer into shape, and then use a tap. But ultimately, the fittings are sealed by the tapered threads. Doing all that, and then it still leaks? It might not be worth the effort.

If it is too bad, it might just be easier too cut it off and weld on a new bung. I had an extra bung welded on each tank for EFI return lines. They are available through ACS, Wicks, and Mark says they make their own at the factory. Or you could make your own.

[nichzimmerman]

Another idea that just occurred to me is to drill it out for a 1/2" NPT and tap it for that. Not sure how much flange would be left over though.

[whee]

Another idea that just occurred to me is to drill it out for a 1/2" NPT and tap it for that. Not sure how much flange would be left over though.

I wanted to do this but determined the remaining flange would be too thin for my liking.

Tapping as is my not be the best idea. The tap will cut both where the bung bent and opposite of it leaving you with a hole that is still out of round.

Perhaps some heat and a steel plug with some kind of lube will get it back straight.

[Battson]

Run a tap upside down (tank hole facing down), use lots of cutting fluid to keep the swarf stuck together, back to tap out and clean it every half-turn. Blow the tank out with compressed air when you are finished. It will be OK, I promise!

Despite all reasonable efforts to isolate my fuel system from swarf, I flushed literally tea spoons full of swarf out of the fuel system during the first flights. It's what the gascolator and fuel filter are for.

[Mark Moyle]

I’d recommend using a 3/8” brass nipple. Bore or dill the ID to reduce the wall thickness...then install with grease. Run in until good and snug. Cut off the nipple so that 1/8”-3/16” protrudes. Then use a long round tapered drift small enough to fit into the brass nipple. Tap tap tap...tighten a little..tap tap tap... that’ll remove most if not all of the deformation. May have to use an easy out to remove the nipple......if you use a tap to clean up the threads you may find the finger strainer may bottom out before tight enough...

[fairchild]

Here is what I'd try-- (but im not normal you understand) Id take a piece of heavy angle iron and cut a piece out a little less tall than the tank is. That goes in the corner below
where it "hit " was. Thread a stainless steel plug into the hole-- maybe the next smaller size of plug-- thread it in until it gets tight. it should be making contact with the bent-in
parts of the threads. Then take a puller and apply pressure from the plug to the angle iron. as you pull --- you should be able to reverse the pushing-in event with the opposite
event-- a pushing out one. You prob. don't have to get it out all the way--- 3/4 of the way might be fine---- enough that you can get the tap back in- and have a tight enough hole
that the roundness is restored before you get to the fat end of the tap. Might take some tinkering to rig the puller.

You wouldn't want to stretch the bung too much because you might get a crack. Might want to do a dye-penetrant test after whatever you do.
I guess this is a variation on marks idea..... If all else fails--- drill out the center big enough to fit a new bong and weld it in--- Lots of chips---
use shop vac on one side and air on the other--- (assuming there has NEVER been gas in the tank---)


T

[Ivan]

Has this been fixed? If none of the suggestions looked good to you because the remaining id is too small to get started, I have a last suggestion.

[svyolo]

Everything I can think of is harder, more work, and riskier than just welding a new bung on. Welding now before the tank has had gas makes the job a lot easier. If you fix it a different way, and it leaks, welding gets to be a bigger job. You have to "inert" the tank.

[nichzimmerman]

Thanks for the input all.

I ended up trying a little of everything (except welding...I don't have TIG machine or skills).

The threads were too warped to thread anything metal into, so tried Mark's suggestion, except with a plastic NPT reducer, which the tapered rod happily disintegrated.

So I just lubed it up real good with thick cutting oil and ran a tap through it. Seemed to work well, and the cutting oil caught most of the shavings.

A 3/8 NPT nipple threads into it very smoothly, but I haven't leak-checked the tank yet. I'm hopeful though.

Thanks again, -Nic