<VV> Fuel Leak

roboman91324 at aol.com roboman91324 at aol.com
Wed Sep 26 16:52:02 EDT 2018


Great advise overall.  I would like to expand on your statement. 
When Engineers design threaded fastening systems, they almost always assume dry thread-to-thread contact.  This dry condition results in the intended and predictable amount of friction between the male and female threads as you tighten.  As you tighten the fastener, the force between the threads' contact faces increase and they deform in the process.  The increased compression increases the frictional force until the design torque is reached.  The result is that there is enough holding force to hold things where they should be while ensuring there is enough friction that the threads will not back out.  Again this assumes dry contact between the threads.  (The use of thread sealers, etc. is another issue.)
When there is a lubricant between the threads, two potentially bad things happen due to reduced friction.  The first bad thing is that you have increased potential to strip the threads.  You imply this with your cautionary note.  Because of reduced thread-to-thread friction, you will compress/stretch/deform the threads significantly more before you reach the specified torque.   This could strip the threads.  That is the case with bolts and such.  In this particular case, the threads will probably survive but you will likely crush the flared end of the tube resulting in fractures.  The second bad thing is that with the reduced friction and the "finger tight" torque, the connection has increased potential to loosen and leak.  Keep in mind that the fitting will be experiencing repeated heat/cool cycles.  A fractured flare or loosened fitting are very bad when dealing with gasoline.
Your suggestions to inspect mated surfaces and even prepping them are good.  However, I would like to modify your grease suggestion.  Put grease ONLY on the inside of the flared tube OR on the male side.  The threads must remain clean and dry.  ALL of the sealing is done on the face of the flare.  Threads are not intended to do any sealing in this application.  This way, you can tighten the fitting normally.  Never use thread sealer or tape.  It is too easy to get that stuff into the fuel system.  The tiny bit of grease in the fuel is soluble in gas and will quickly dissipate. 
If you suspect you have a bad connection, the best solution is to cut off the flare and put a new flare on it.  I think you can borrow a tool from your FLAPS if they have one.  Better yet, bring your tube with you and perform the operation in the store.  Make sure the cut is square to the axis of the tube and the face is clear of burrs from the cut.  Oh, and make sure the female fitting is on the tube before you flare it.  Don't ask how I know about this.  :-)
In a message dated 9/26/2018 9:00:11 AM Pacific Standard Time, virtualvairs-request at corvair.org writes:

Message: 1
Date: Tue, 25 Sep 2018 22:42:51 -0400 (EDT)
From: JUDY HOOK <judynrandy at comcast.net>
To: virtualvairs at corvair.org
Subject: <VV> fuel leak
Message-ID: <485071148.3836.1537929771441 at connect.xfinity.com>
Content-Type: text/plain; charset=UTF-8

Try this wonderful trick. Disassemble the fuel lines and physically inspect each sealing surface. Check for things like micro-cracks and deep scratch marks. Also, a small piece of dirt or debris stuck to the fittings will cause a leak, too.

Make sure they "mate" up properly. You might even try lightly sanding and polishing each sealing surface area with a piece of fine grit sandpaper to insure smoothness and a good sealing surface area. Now for the kicker - Lightly coat the sealing surface, tube, and fitting with some axle grease. I use Amsoil's synthetic grease. Then, assemble everything just finger tight. When you go to tighten things, just tighten them slightly. With the grease on them, it's super easy to over tighten them. I usually use the "just snug, then a little more" formula. Remember, you can always tighten it a smidge more, if needs be.

Hope this helps,

Randy (Cap'n) Hook

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