Some K gas tank questions

[Los_gatos]

Hi, first post.

I just recently purchased a project 92 K75. There's a slight leak from the gas tank at the typical low spot along the seam. It looks like someone has tried to put some Permatex or JB weld on the outside of the tank to seal it, but it still weeps. The tank look good inside other than the low spot on the left side. I've searched the forums for potential remedies, but I still have a few questions:

1. I was thinking of using JB Tankweld on the inside of the tank. Is that advisable? Most posts I've seen suggest the outside, but didn't see any about using it on the inside.

2. I was thinking of then using red kote over the the Tankweld, or even without the Tankweld. Since most of the tank is in good should I just red kote the seam or most of the bottom?

3. If I use red kote, or por or something else, how do I go about blocking off the metal fuel lines to prevent clogging? Particularly the return line. The other lines I think I could maybe put a rubber plug over?

Thanks in advance.

[triplek]

Have the seam welded to repair it. There isn't really an acceptable substitute.

[The Mighty Gryphon]

And don't bother with the coating.  The aluminum is okay as long as you don't let stale fuel sit in it for years on end.

[blackie1]

https://www.motobrick.com/index.php?topic=15474.msg137502#msg137502

jb weld on outside worked great for me

[Duckbubbles]

I used a product called Kream or Kreem to coat the inside of the tank.  It is intended to coat fuel tank interiors.  I didn't coat the whole thing as they suggest but put it mainly in the trough made where the upper and lower tank halves are welded together. It is maybe 1/4 inch thick in that area at it's deepest.  Several years now with no problems.
I originally used JB weld externally but it finally started to leak again at that spot.

Frank

[Los_gatos]

Thanks for the recommendations. I asked our local motorcycle FB group and found someone who would tig weld the leaking location. Would painting the seam with the red kote I bought help prevent potential future corrosion, or should I just forget about and don't let it sit for too long?

[The Mighty Gryphon]

Use the bike regularly and don't bother with coating the tank.  If you are going to leave it unused for an extended time either fill the tank with non-ethanol fuel and some Stabil or drain the tank completely.

[Los_gatos]

Here's a pick of the holes in the tank for those playing along at home.

[Los_gatos]

Preliminary update: Had the tank welded on the outside a couple times. New welds kept exposing new holes to weep from. Tried seal-all on the exterior and that seemed to plug it up after a short trial.

[natalena]

Sidebar: has anyone tried the aluminum brazing rods on a K tank? Looks like a magic solution if prep is really thorough.

[Los_gatos]

From what I've seen in other threads, it's hard to get the aluminum up to temp without over cooking it. I recently watched a ProjectFarm video and he had good luck with some fairly low temp rods.

[Duckbubbles]

From what I've seen in other threads, it's hard to get the aluminum up to temp without over cooking it. I recently watched a ProjectFarm video and he had good luck with some fairly low temp rods.

This made me think how about solder?  I don't know what it would take to make it stick to the aluminum, maybe flux?

Frank

[Laitch]

Welding unites metals by melting them together. Rod or wire with flux or gas shield to prevent impurities in the bond is used to unite the pieces. Aluminum welding must be done smoothly and rapidly because of aluminum’s rapid rate of liquifying when it reaches the melting point. The heat and filler must be moved along rapidly or holes will be blown into the material being welded. Welding can blow holes in thin sheet steel, too, if it it isn’t done rapidly enough.

Brazing unites metals by raising their surface temperatures enough to adhere together using filler rod containing flux but not at a temperature high enough to melt them. The filler applied to the pieces creates a strong bond that can withstand vibration. The lugs that join bicycle tubes are often brazed. Project Farm is discussing brazing and brazing rod.

Solder is similar to brazing in some ways but uses a lower temperature to bond similar metals together. It’s more like glue. It isn’t the choice for filling holes. Usually patches are used over holes and united with the metal beneath by capillary action of solder and heat. Flux in the solder, or applied before soldering, prevents impurities in the joint.

Brazing would be the choice for an amateur attempt at repairing holes in an our aluminum fuel tanks' seams but plenty of practice should be done on sheet of a similar thickness and grade before the brazing attempt or the hole will grow during repair because the metal was overheated and melted during the fill process.
JB Weld seems to work well enough for most of us, if we're able to follow directions and don't ask too much of it.