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Fuel leak thru BNC fuel sender plug

TIPSYNIPPER

Active Member
Hi Guys (Girls)
I am a new RV4 owner and have found that the BNC fuel tank sender "chassis plug" at the wing root are leaking through the center of the connector. This is covering the small PCB in fuel and is corrupting the data for the AFS3400 EFIS so I get erratic fuel contents indications.
Is this a common issue, is there a repair scheme?
I have no invoice to see where they were purchased from, can anyone advise a replacement source?

Thanks for your help.
Neil

photo1_zps86eadba7.jpg.html
 
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neil,
to post a photo, upload the photo to photobucket, or any other photo hosting site, and place the link to the photo in your post on this forum.

upon uploading to photobucket, photobucket generates a link to the photo that I then copy into this forum, and viola, the photo appears in my post. hope that helps.
 
...thanks, will do, shame we can't upload direct from the confuser, I don't use photobucket but will sign up for it.
Neil
 
Needs more sealant on the inside

This problem was commonly discussed about 5 years ago and comes up from time to time.

The most likely cause is the application of tank sealant. In order to prevent fuel from seeping through the center connector, the whole BNC inside the tank and a few inches of the connected wire need to be covered in sealant.

If the BNC is only sealed around the penetration hole, fuel will seep into the wire strands and migrate into the connector and around the center pin.
 
Hi Bill,
Thank you very much for the prompt reply.
That sounds very much like the issue I have. What would be your recommendation for a repair scheme please?
The fuel tank sealant comes in a large tube, I will only need a small amount, any suggestions?
Neil
 
proseal

Hi Bill,
Thank you very much for the prompt reply.
That sounds very much like the issue I have. What would be your recommendation for a repair scheme please?
The fuel tank sealant comes in a large tube, I will only need a small amount, any suggestions?
Neil

There must be RV builders over there. Almost every builder has some left. If not, Vans sells a smaller container.
Depending on how the access plate was attached, you may need some to reseal it as well.
 
Try LAS

Neil

LAS aero sell a small kit that you can mix up as much as you need and keep the rest for another time.
Also it looks like if you open the inspection plate it would be a good idea to refit it with sealant as well plus put some on each screw as you refit it.

Cheers

Peter
 
Thanks Guys,
Larry, your blog helps no end as I am now better informed as to what I am going to find when I open up the inspection hatches. What have/are you using to seal your inspection hatches? I am reluctant to use proseal, as it is a bugger to get apart once cured I would think, and if I need to get inside the tank again that may be a problem. I am thinking of using Permatex?
If the wire is just soldered to the center pin I don't see that fuel seeping down the wire can be a problem, it must be coming from around the center pin, possibly due to excess heat when soldering and not coating the chassis plug with sealant? or even a defective chassis plug? I will know more once I get inside. I think maybe using permatex to seal the chassis plug?
Neil
 
Hi Bob,
Thank you very much, i may have some in the workshop, I will check tomorrow and if not would very much like to take you up on your offer.
Where are you based? (off on a jolly tomorrow!)
Neil
Ps: pm me your mob' if you like?
 
Sealing access panel

Thanks Guys,
Larry, your blog helps no end as I am now better informed as to what I am going to find when I open up the inspection hatches. What have/are you using to seal your inspection hatches? I am reluctant to use proseal, as it is a bugger to get apart once cured I would think, and if I need to get inside the tank again that may be a problem. I am thinking of using Permatex?
If the wire is just soldered to the center pin I don't see that fuel seeping down the wire can be a problem, it must be coming from around the center pin, possibly due to excess heat when soldering and not coating the chassis plug with sealant? or even a defective chassis plug? I will know more once I get inside. I think maybe using permatex to seal the chassis plug?
Neil

Neil
Thanks
Sealing the access panel is discussed almost as much as primer wars.:eek:
After reading through threads, there are two or three common practices.
1. Proseal with no gasket
2. Titeseal with gasket
3. Permatex.

I'm still on the fence but leaning to #2. I put a flop tube in the left and standard pickup on the right. I considered #1 on the right and #2 on the left in case the flop tube needed to be inspected later.

You are probably correct and the fuel is leaking because the BNC was not sealed all the way back to the sender wire.
 
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You probably can't reach it in a finished tank, but it's a good idea to also seal the wire at the terminal on the far end, where it attaches to the inboard capacitance plate. fuel can wick down the length of the wire, and if the wire isn't tinned well at the BNC, fuel can find its way through the connector.
 
I did try Permatex on the connector but started leaking again after a few months. ProSeal solved the problem.

Ken
 
Gents, thank you for your input. I will seal the fitting in due course.
I can't see that the fuel can "wick" down the wire to create a leak, as the wire is soldered to a solid center terminal in the BNC plug.
Regards,
Neil:)
 
....I have now taken off the fuel tank cover and can see the BNC chassis plug and can see why you suggest the fuel could make its way down the wire. The back of the plug has been coated with proseal, and looks like it has been done well. This in effect creates a "sleeve" to connect the "tube" of the wire insulation to the plug.
For a repair scheme I intend to scrape away a small area of insulation on the side of the wire to expose the conductors, use a vacuum pump (its a fridge compressor that will pull a good vacuum) on the BNC plug and hopefully "suck" Cyano into the wire core. I have vacuum gauges from servicing automotive aircon' and will hopefully see the change in vacuum to establish if the process has been successful.....will let you know!
Thanks for your input.
Neil
:eek:
 
vacuum ?

I just tested my tanks with air and they have a leak thru the BNC connector. I think the method you suggested below might work. What is this "Cyano" you suggested? I'm wondering if I could do this without open up the tank, just apply a vacuum and suck it into the leak?

....I have now taken off the fuel tank cover and can see the BNC chassis plug and can see why you suggest the fuel could make its way down the wire. The back of the plug has been coated with proseal, and looks like it has been done well. This in effect creates a "sleeve" to connect the "tube" of the wire insulation to the plug.
For a repair scheme I intend to scrape away a small area of insulation on the side of the wire to expose the conductors, use a vacuum pump (its a fridge compressor that will pull a good vacuum) on the BNC plug and hopefully "suck" Cyano into the wire core. I have vacuum gauges from servicing automotive aircon' and will hopefully see the change in vacuum to establish if the process has been successful.....will let you know!
Thanks for your input.
Neil
:eek:
 
Hi Gary,
Believe it or not I have not been back to the a/c since I topped the tanks. However, I hope it is sorted.
What I did:
1: Remove some insulation on the side of the wire to expose the stranded core. I used a new Stanley knife blade (with some grease on the blade so any cuttings did not fall into the tank) to carefully cut an area of insulation off about 1" long.
2: Using an old fridge compressor on the vacuum side (I used to use it to evacuate car a/c systems before refilling them) so had gauges to see what the leak-back was. (This gave me some positive evidence the leak was rectified before refilling the tanks.)
3: With the vacuum pump running applied some cyano-acrilate (super-glue) to the side of the wire to allow the vacuum to pull the thin glue into the wire strands. This had a very positive effect on the leak down, but just to be sure I then covered the exposed area of wire and recoated the back of the BNC plug whilst the vacuum was applied with fuel tank sealant (from LAS)
Refitted the inspection hatch using a fuel proof sealant (Blue Hylomar will do I think which is readily available, but I used Bondloc B5180 ( http://www.bondloc.co.uk/#/b5180/4549958340 )
I will be going over to the a/c tomorrow, so will know then as I topped the tanks before I left.
LAS do a fuel proof grease which as a "belt and braces" could be put into the BNC chassis plug, but I don't know if that would affect the performance of the Capacitive readings for the fuel gauges. I would not think it would.
Good luck. I will report back tomorrow!
Neil
Ps: If you are using the a/c for aero's have you fitted "flap valves" to the innermost baffle? I need to check this as during slow rolls or knife edge flight the fuel will move to the far end of the tank (toward wingtip) causing fuel starvation. I don't know if I can achieve this through the inspection hatch (with the tank removed) if it has not been done.
 
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My BNC connectors both leaked when I first leak checked the tanks in 2006 and I had pro sealed as in the above posts. I didn't want to tear into the tank so I pro sealed a 90 degree connector on to the leaking connectors. I covered the leaking connectors from the tank with the pro seal and then put the 90 degree connector on and covered the whole thing with more pro seal. It was easy to do since the tanks were not on the airplane at the time. So far 650 hours and 8 years with no leaks.:)


Hi Bill,
Thank you very much for the prompt reply.
That sounds very much like the issue I have. What would be your recommendation for a repair scheme please?
The fuel tank sealant comes in a large tube, I will only need a small amount, any suggestions?
Neil
 
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