Another fuel leak

[WintrSol]

I kept smelling gas in the garage, so I changed the fuel cap - no change. So, I looked under the tank, and the line to the belly tank was damp. I pumped the gas into a can, and found I'd lost nearly 4 gallons over about 2 months. I assumed that the brazing for the belly tank bung had cracked, because of where the leak appeared. Lifted the back of the tank for access to the connections, then lifted it more to disconnect the petcock, and the petcock moved. Whenever I have to remove the tank, I always check the torque on it, but it was loosened. After removing the tank, I took the petcock off, and found the little O-ring seal was compressed flat and fairly rigid - no seal, and no resistance to the petcock turning. No apparent damage to the brazing or the sealant applied over it, so going with a new O-ring.

Just another thing to check when you smell gas.

[Foozle]

I, too, have a belly tank - and any whiff of gas immediately sends me into a panic re: the bung brazing - which, due to a local unavailability of competent welders, seems like the weakest link. 

It's nice to be reminded this can still be caused by a "just" leaky petcock.

Glad you got it sorted out.

Terry

[WintrSol]

Something to check, anyway. After over 23 years, that O-ring was compressed to the point it couldn't hold a seal. Unfortunately, the parts diagrams don't show the size, so I had to order it from partzilla; had some other parts to order, so it's not like I paid more for shipping that for the part.
Also, I already bought a stick of JBWeld Tank Weld, in case I have to re-coat the brazing.

[MarkT]

It's easy to have a leak from the bung brazing.  I did it myself and had to remelt and add more brass.  So if I could FUBAR it so could anybody else.  You learn to be very thorough after you realize the slightest imperfection can leak the very low viscosity fuel.  Inspect it under magnification.  Screw in a plug, put in some fuel and do a leak test before buttoning it up.  I suspect it could be TIG or even MIG welded instead if you are skilled but brazing is easier as lower temp, not going to burn holes in the thin tank wall.  Also takes less and cheaper equipment.

BTW I had never welded or brazed on fuel tanks before.  I found with proper precautions it's not rocket science to avoid fire.  It can even be done with gas in the tank - I did that.  The precaution is ensure there's no oxygen inside.  Set up your MIG gun to feed the argon/CO₂ in the petcock opening, obviously disconnect the wire feed. I screwed a 6" nipple into the threads of the petcock hole, inserted the mig gun in that and wrapped it with electrical tape - probably not necessary. Open the top filler cap.  Run the gas for 5 minutes before you light the oxy/acetylene torch.  There was several ounces of gasoline in there (the second time I did it, after realizing I didn't need to be as careful as the first time.)  Some yellow flame will light at the bung hole you are brazing when the gas fumes mix with the outside air. But not inside the tank.  So you don't have to purge the gas liquid or fumes if you do it like this.  There are videos on youtube of a farmer welding on a gas tank with gas in it, he ran exhaust into the tank filler to purge the air out.

[WintrSol]

Instructions call for silver solder instead of brazing, but since I have some sealant covering mine, I don't know which it is. Not removing the coating, unless the O-ring doesn't completely fix the leak.

[Foozle]

This past fall, I upgraded to an I/S tank and had a local radiator shop do the bung installation.  Much earlier, I gotten a spare directly from Roger at R & M - and supplied them with detailed instructions.  Getting a good vibe re: their professionalism helped ease my anxiety.

I'm not sure what process they used, but I leak-tested the tank with water several times before installing and filling it with gas - and it's been good so far.  I'll keep some JB Weld on hand, just in case.

The replacement bung didn't screw in quite as far as the coupling on my standard tank, but this hasn't caused any issues (and actually made connecting the belly tank hose a little easier).

I've probably now got more fuel capacity than my aging a** can endure in the saddle, but I really think the larger tank just "fits" the overall look better.  I should be good for as long as I'll be on two wheels (knock on wood!).

Terry

[MarkT]

Silver soldering and brazing are actually nearly identical in use and application.  The main difference is slightly different temps between the filler material.  Having worked with these proceses since '99, I took his recommend with a grain of salt - he could have specified either.  Here it's explained at https://weldlover.com/how-strong-is-silver-solder/
There's more detail there, temp charts etc if you want to read it.

People usually mix brazing and silver soldering because of the great extent of similarity in both techniques. If you also have the same kind of misconception, then we have identified two key dissimilarities between brazing and silver soldering, which are:

    Silver welded joints demand overlap of metal for stronger bonding which is not the case with brazing
    Silver soldering alloys have higher fluidity than brazing fillers

The fillers used in brazing are typically made up of copper metal, but these fillers can also be alloys with high nickel content. Besides, the other metals found in these alloys are zinc, tin, silicon, phosphorous, and Silver. The silver solders are mostly brazing fillers but with a higher proportion of Silver in the overall composition.

The higher fluidity of silver solder means it may drip on through without closing a gap. Harder to use. Such behavior can be adjusted by controlling the phosphorous content. Don't want to mess with the chemical composition, just want to get this done with what I have on hand.  I want to use a bit thicker, more viscous fill.

BTW I changed the design of my original belly tank install, to my own design of retaining the gravity feed and replenishing it with the belly tank.  Mainly so I only run the fuel pump for a few minutes instead of continuously.  That pump has failed for many.  This change meant I needed to remove the bung outlet with it's internal tube and install a bushing that will drain off the tank bottom.  You can remove a brazed part easily (same for silver soldered).  Not so if welded.

I also upgraded to an I/S tank and installed a bung outlet there.  This one is also a bushing so I can drain all of the gas through the bung hole.  This time was easier as I knew the shortcuts.  Total volume is about 9.75 gal.  The fuel comes in handy when you pull a heavy camper, or ride out west with long hauls with no gas, or with riders who might run themselves outta gas.  I made mine to easily share gas with an extra petcock.  http://www.valkyrieforum.com/bbs/index.php/topic,84264.0.html

[WintrSol]

I think the location of the pump leads to it quitting. That location is inches from a header pipe. Mine stopped on a remote road in W. Virginia and blew the fuse that feeds it. After sitting by the roadside a while, and replacing the fuse, it worked fine again. I fashioned a heat shield for it, and haven't had it quit since (knock wood)..

[MarkT]

So did I, on adding a heat shield.  Put a pic of it at the above link. Or here:

[Foozle]

I have the same heat shield as Mark - purchased, in fact, from Horseapple Ranch.  I never had a problem with the fuel pump, but know others who have - which I too attributed to heat from the exhaust pipe.  I just wanted to avoid any future issues.

I had a buddy who covered the inside of the right exhaust in fiberglass heat wrap - and another who did the same with the fuel pump.  Both of these solutions also seemed to work.

Terry