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  #1  
Old 04-24-2021, 05:26 PM
00Dan 00Dan is offline
 
Join Date: Nov 2016
Location: Atlanta, GA
Posts: 222
Default Fuel tanks venting through caps

I know the fuel tank vent line design in the -4 makes it exceedingly difficult for any fuel to exit through the vent. What Im seeing is my tanks are venting fuel through the center of my caps after a fill up. I have the old black o-ring caps, for reference.

Is this a common problem? Should I look at rebuilding my caps or is this something Ill just have to live with due to the vent line design?
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  #2  
Old 04-24-2021, 05:40 PM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 1,448
Default Rebuild the caps

The caps will leak as they age. Rebuild, keep lubricated and maintained. The vent system if built correctly will do its job. If your plane is sitting unlevel, you may still get some out of the cap, but dont overfill past the bottom of the cap flange. Remember, if fuel comes out the cap, rain goes in the cap. The vents are critical to continued fuel flow to the engine, and you need to be sure they are open and unobstructed , but the cap should be completely sealed. The rebuild is simple and I keep spare O-rings and the cam pivot on the shelf ..cheap insurance.
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  #3  
Old 04-24-2021, 10:13 PM
dnh98221 dnh98221 is offline
 
Join Date: Oct 2018
Location: Anacortes
Posts: 27
Default Fuel caps

I lube mine with Vasoline, been doing so for many years.
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  #4  
Old 04-25-2021, 12:01 AM
Lt Dan Lt Dan is offline
 
Join Date: Dec 2014
Location: Utah
Posts: 100
Default

Quote:
Originally Posted by fixnflyguy View Post
The caps will leak as they age. Rebuild, keep lubricated and maintained. The vent system if built correctly will do its job. If your plane is sitting unlevel, you may still get some out of the cap, but dont overfill past the bottom of the cap flange. Remember, if fuel comes out the cap, rain goes in the cap. The vents are critical to continued fuel flow to the engine, and you need to be sure they are open and unobstructed , but the cap should be completely sealed. The rebuild is simple and I keep spare O-rings and the cam pivot on the shelf ..cheap insurance.

Ive noticed a similar issue recently. Where does one find the part numbers, etc for the parts you mentioned?
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  #5  
Old 04-25-2021, 05:17 AM
Skysailor Skysailor is offline
 
Join Date: May 2011
Location: Atlanta, GA
Posts: 287
Default More than one O ring

Those seeing "venting out the fuel caps" have bad O rings as the Usher caps are not vented. There is a small hidden O ring around the shaft going through the cap in addition to the large one you can see when removing the cap. It is likely your small O ring needs replacement. You will have to dismantle the cap to get to the small O ring.
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  #6  
Old 04-26-2021, 06:56 AM
219PB 219PB is offline
 
Join Date: Aug 2014
Location: Victoria, Tx
Posts: 515
Default O-Ring size

Are the O-rings from Van's Viton? Their website does not say, and the description states "The brown O-rings are generally auto fuel resistant, but their tolerance for the newer oxygenated auto fuels is unknown". If they were Viton, this statement would not be necessary.

Does anyone know the sizes of the two O-rings? Would be simple enough to source.
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  #7  
Old 04-26-2021, 07:23 AM
00Dan 00Dan is offline
 
Join Date: Nov 2016
Location: Atlanta, GA
Posts: 222
Default

Along the lines of the o-ring discussion, what is it about the brown o-rings that makes them incompatible with the old caps? Did the castings change? Vans website says the new caps will fit any receptacle so it cant have been outer dimensions that changed.
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  #8  
Old 04-26-2021, 07:31 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Default

Quote:
Originally Posted by 219PB View Post

Does anyone know the sizes of the two O-rings? Would be simple enough to source.
The o-ring sizes are standard and listed on the picture posted above.
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  #9  
Old 04-26-2021, 09:24 PM
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pjc pjc is offline
 
Join Date: Apr 2012
Location: Tampa, FL
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Default

Quote:
Originally Posted by lr172 View Post
The o-ring sizes are standard and listed on the picture posted above.
Those with older kits should note that the old caps also use 2 o-rings, but of different size. For the old caps you need 1 size 326 and 1 size 011.

Not sure when the switch from old to new occurred. Mine is a 1992 kit RV-6.

More here ... https://vansairforce.net/community/s...d.php?t=193677

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  #10  
Old 04-27-2021, 06:16 AM
219PB 219PB is offline
 
Join Date: Aug 2014
Location: Victoria, Tx
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Default

Quote:
Originally Posted by lr172 View Post
The o-ring sizes are standard and listed on the picture posted above.
Sorry, my bad.
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