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  #1  
Old 06-17-2018, 08:27 AM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 2,021
Default QB FUEL TANK CAUTION

For those with QB wings and therefore finished fuel tanks, here?s something to check before installing the fuel level sender and large inspection plate opening on the inboard tank rib with pro seal. The B-nut on the inboard end of the tank vent line may not be tight. It?s easy enough to check and exercising due diligence, it should be checked - just like the proper bolt torque on all the Z-bracket bolts. I?ve found these loose, but for some reason I didn?t think to check that B-nut. If you have fuel dripping out of your vent line when the tank if fairly full but the outboard end of the vent line is ?above water?, then your B-nut is probably loose. It shows up when the air in the fuel tank heats up, has no where to go and forces fuel up and over the loop in the vent line. We?ve had 4 of these at our airport all on QB RV wings. I had the joy of removing the tank and then the inspection plate on my right tank to gain access. The nut was barely finger tight. This won?t show up on a tank leak test because the vent bulkhead fitting is capped off on the outside.

Here?s another thing to consider when doing this part of your project. You might want to run a dedicated ground wire to one of the fuel sender mounting screws if you?re pro sealing these in place. My left fuel level sender had an intermittent indication, going from correct reading to empty intermittently, with warnings from the G3X about an empty fuel tank. I removed one of the mounting screws on the sender, cleaned off the pro seal, installed a wire with a ring terminal and a lock washer under the screw and then re-prosealed it. The lock washer insures a good ground connection. This ground wire is grounded under one of the inboard Z-bracket bolts. This is easy to do without removing the tank. I put one on the right tank also, just to be sure, since I had the tank off anyway. Seems I had enough proseal under the sender mounting screws and/or the inspection plate mounting screws to disrupt a smooth pathway to ground. That fixed my indication problem.
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RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
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JAN2021
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  #2  
Old 06-17-2018, 02:00 PM
vic syracuse vic syracuse is offline
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Join Date: May 2005
Location: Locust Grove, GA
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Default SB in 2006

Hi, Scott. I don't know what vintage your kit is, but there was a SB issued in 2006 to check on the B nut inside the tank and safety wire it. Here's the link:

http://vansaircraft.com/pdf/service_.../sb06-2-23.pdf


Vic
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  #3  
Old 06-18-2018, 04:34 PM
Scott Hersha Scott Hersha is offline
 
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Location: Cincinnati, OH
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Default

Vic,
That?s not the B-nut I?m talking about. I?m talking about the one that attaches the fuel vent line to the 90 degree bulkhead fitting inside the tank. There is no safety wire on that nut and it?s normally tight from the factory on a QB wing tank - but I?m just saying it should be checked. No SB on this one.
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SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO
JAN2021
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  #4  
Old 06-18-2018, 05:17 PM
Lars Lars is offline
 
Join Date: Nov 2005
Location: Davis, CA
Posts: 1,189
Default

Have found a few myself including my own 7 another 7 and a 9. All wings were assembled in the 2007-2008 time frame. And to be clear, vent line b-nuts as Scott described, not fuel pickup lines.
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  #5  
Old 06-18-2018, 05:34 PM
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Steve Melton Steve Melton is offline
 
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Default

they probably just hand tighten those. how else could it be loose?
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Last edited by Steve Melton : 06-18-2018 at 05:49 PM.
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  #6  
Old 06-18-2018, 07:36 PM
Scott Hersha Scott Hersha is offline
 
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Location: Cincinnati, OH
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Default

I?m pretty sure they are supposed to be properly torqued on QB tanks, but occasionally they miss that step and as Steve said, are just hand tightened. One of the tanks at our airport had the B-nut slid all the way up the vent line to the next rib. It?s easy to check before installing the fuel pick up line (the one that needs to be safety?d) and fuel level sender plate. I just wanted to caution QB builders to not assume that connection is tight, and also make sure you check z-bracket bolt torque.
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SH
RV6/2001 built/sold 2005
RV8 Fastback/2008 built/sold 2015
RV4/bought 2016/sold/2017
RV8/2018 built/Sold(sadly)
RV4/bought 2019 Flying
RV6/Used kit purchased 2021 building
Cincinnati, OH/KHAO
JAN2021
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  #7  
Old 06-18-2018, 09:11 PM
artrose artrose is offline
 
Join Date: Jan 2011
Location: San Antonio area
Posts: 86
Default

I had that exact same situation with the right tank on my 2005 6A. The original builder neglected to properly tighten that nut inside the tank. I diagnosed the issue by plugging the end of the vent line with my finger thru the filler neck, and then had a helper blow on the other end of the vent tube. You could hear him blowing bubbles inside the fuel tank. For several years when I parked the plane, I would just loosen the filler cap so it would'nt push fuel overboard.
Recently, I pulled that tank to repair some small leaks around the sender, and I fixed the problem with the vent. Unfortunately, I still have a small fuel seep in the top of the inboard rib in that tank, and it will need to come off again next inspection. I used the green loctite to fix the left tank fuel seeps last year, and I'm going to try it again on the right tank. I'm really tired of messing with leaky fuel tanks.
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