61 B model fuel leak

[JimC67]

I have a seep and a leak from two nuts on my bottom, inboard tank cover. The screws just spin, and won't come out. 

Looking inside the empty tank with a borescope, I see these. Can't get to them to put a wrench on them so I can back, them out. Can't unscrew them.

Looking at the other panels, they're all like this. Same nut

My IA has done tank repairs on Mooney's before and said they're normally a dome type nut. 

Any idea's on how to get this leak to stop?

[47U]

25 minutes ago, JimC67 said:

Any idea's on how to get this leak to stop?

The ‘approved’ way, would be to pull the panel on the top of the wing, then you have access to the nuts.  Remove the improper hardware, install dome nuts, reseal the panel, and reseal the top panel.  After cure check of the sealant, leak check the tank with full fuel.

I don’t think you’ll have any luck trying to reseal the hardware fishing through the fueling port.  I think you’ll end up pulling the top panel, regardless.  Making a big mess with sealant inside the tank could create a safety of flight issue.

If your tank sealant is in otherwise good condition, you might get by (for a while) just resealing the hardware that’s leaking.  Probably remove the hardware, strip the area, reinstall the hardware, and then sealant.  Not sure if your A&P would concur with that option.  It would not be IAW any Mooney tank repair guidance I’m aware of… surely (?) Mooney used dome nuts in the tanks in the B model.  You might check to see if the other tank uses the same hardware.

When was the last tank work done in the logbooks? 

[JimC67]

5 hours ago, 47U said:

The ‘approved’ way, would be to pull the panel on the top of the wing, then you have access to the nuts.  Remove the improper hardware, install dome nuts, reseal the panel, and reseal the top panel.  After cure check of the sealant, leak check the tank with full fuel.

I don’t think you’ll have any luck trying to reseal the hardware fishing through the fueling port.  I think you’ll end up pulling the top panel, regardless.  Making a big mess with sealant inside the tank could create a safety of flight issue.

If your tank sealant is in otherwise good condition, you might get by (for a while) just resealing the hardware that’s leaking.  Probably remove the hardware, strip the area, reinstall the hardware, and then sealant.  Not sure if your A&P would concur with that option.  It would not be IAW any Mooney tank repair guidance I’m aware of… surely (?) Mooney used dome nuts in the tanks in the B model.  You might check to see if the other tank uses the same hardware.

When was the last tank work done in the logbooks? 

The hardware is the same in both wings, top and bottom.

The last tank re-seal in the logbook was the left wing in 1989. Nothing noted for the right tank. 

The biggest problem we're having is just getting access. You can't pull the panel if the hardware just spins. That's our main issue. Other than that, I agree with your assessment.

[Aerodon]

at some point just destroy the removable panel for access and replace with a new one?

[47U]

5 hours ago, JimC67 said:

The hardware is the same in both wings, top and bottom.

Top and bottom panels installed without using dome nuts.  That’s a challenge.  How did they put that together?  Anyone?  

Can you access through the fuel sender hole in the cabin?  It’s not very big, but I think less challenging than the filler neck on top of the wing.

In the end, you may end up with the suggestion by @Aerodon and cut access holes in the panels.  I’m thinking the panels would have been made on a fixture so the hole pattern ‘should’ match.

[JimC67]

21 hours ago, Aerodon said:

at some point just destroy the removable panel for access and replace with a new one?

Hadn't crossed my mind, but that would indeed solve the problem. Any idea on the part numbers I'd need? I've got an old parts manual, but it's kinda useless

[47U]

1 hour ago, JimC67 said:

Any idea on the part numbers I'd need?

Near as I can tell, fuel tank access panels are pn 210099-1.  Same part number top and bottom access panels.  Same part number in the mid-60s IPC, so there should be some available through the salvage yards, for sure.

[JimC67]

Thank you

 

[JimC67]

20 hours ago, 47U said:

Near as I can tell, fuel tank access panels are pn 210099-1.  Same part number top and bottom access panels.  Same part number in the mid-60s IPC, so there should be some available through the salvage yards, for sure.

Those are the panels. Looking at used one's, I came across a couple from a C model that have the same nut plates. Maybe an early factory thing before they figured out dome nuts were better? 

We're removing the panel and putting dome nuts on it, so we don't run into the issue again

[47U]

1 hour ago, JimC67 said:

Maybe an early factory thing before they figured out dome nuts were better? 

I remain confused.  But, I’m not a fuel tank guy, either.

By not employing nut plates, dome or not, how do you hold the nuts from turning when the last access panel is installed to close up the tank?  And how are those nuts sealed?  Installing hardware with sealant isn’t unheard of, but mostly as last-ditch effort to stop a leak and avoid pulling an access panel to make a proper repair.  Maybe I should go read a mx manual…

Glad you have a way forward.

[47U]

22 hours ago, JimC67 said:

Maybe an early factory thing before they figured out dome nuts were better? 

The alphabetical parts listing in the early IPC (‘61-‘64) includes the dome nut plate, pn ESNA-22-NAIK-02, applicable to production serial number 1701 and on.  The mx manual (104) addresses sealing of fasteners and nut plates only in generic language.  Whoever used plain nuts installing the fuel access panels didn’t follow the IPC for proper hardware, in my opinion.