Fuel tank seam leak

[nhmaf]

Well, at some point, there has to be a first time for everything...

My 3 motorcycles were tucked away in the back for the garage for their long winter's nap.   Fuel tanks were filled up and had a good dose of Marine formula STABIL and/or SeaFoam in them to prevent varnish/gunk and water damage.  Around New Year eve, I noticed a strong gasoline odor coming from the R100/7.  A day or two later, I noticed some wetness on the cement under the engine.   A day or two after that I discovered the left side of the engine wet with gasoline, and the left side fuel line was soaking wet with fuel.   I checked the fuel bowls, pulled the fuel line fromt he petcocks and noted that the fuel wasn't going through the line(s), nor was it overfilling the carb bowls.   I checked the dipstick - oil level normal and not mixed with gasoline-good.  I noticed the starter cover, engine badge were also wet with fuel.   Oh....... fudge.

The fuel leak seemed to stop after a bit.   I opened the filler cap and noted that the fuel level in the tank was somewhere around 2/3 full - over a gallon had leaked out but the level was now somewhat below the internal "hump" where the tank goes over the frame backbone.   I pulled the tank, drained the gas, and, as I feared, the tank seems to have been leaking at the udnerside of the center seam where the 2 halves are joined, in the area directly beneath the filler cap.   The tank itself (inside) still has most of the original red liner and doesn't appear to be rusty.   But I figure that at least some bit of rusting must have compromised the weld joint (or is it hard-soldered?), or perhaps some strange form of metal fatigue.  I cannot find any evidence of rubbing, denting, etc, and the undertank M/C has not been leaking/corroding.

I have to do some cleanup of the tank, but I am wondering if I thoroughly clean the inside and re-line the tank with tank sealer kit if that will adequately do the job, or should I see someone about welding the tank, or try to silver solder it with propane torch, etc (and yes, that will precipitate a repaint).

At first I thought that one or both petcocks were leaking, then I thought maybe the very bottom edge of the tank had rusted out, but neither was the case.   I haven't seen an airhead (which doesn't go on motocross/offroad trails) have a tank seam leak in this place before.

Suggestions?

Mike

[tvrla]

That IS an unusual place to leak - normally it's down by the petcocks.

This isn't due to rust but parting of the seam?

New paint wouldn't be needed in that spot. Just touch it up -- it is the underside, after all! I'd think brazing would be the best fix for it.

[nhmaf]

I'm letting the tank air-dry for a bit and will try to clean it up some more inside and out to see - but it was leaking enough to drain out about 1.5 gallons over the course of a few weeks.  After taking the tank off, I saw that the  frame tube area just behind the M/C was wet with fuel, and even the left side coil was wet with fuel.  It had been dripping slowly on the top of the starter cover and running down the side of the engine, and also it seemed to run down the side of the tank, along the lower edge to the left petcock, and then down the outside of the fuel line (which was soaked).     I've seen tanks leak at the seam in this area when they were dual purpose, steel tanked bikes that saw alot of off road jumping, etc and the seam parted.   I don't know what the PO did with it, but I've had the bike a couple years now and it has only seen paved roads and maybe 100 miles of graded gravel roads.   Weird.

[Barry]

Here's me thinking a virtually intact red liner means the tank is good and solid.  

That is an unusual place to leak and to rust so it will be interesting to see what the cause was. Not a simple problem then.  Depending on how much of a gap there is I might be tempted to try high temperature high strength soft solder to minimise the paint damage. You need an active flux to solder steel but it can be done.

[montmil]

Will not the solder/braze/weld repair ultimately lead to R&R of the heat damaged liner?
In this case, it seems one thing leads to another.

[Bob_Roller]

POR 15 will seal seam leaks .

One drawback, is that the original OEM liner has to come out before you apply it .

So, which ever way you go, it's going to be a bit of work .

[davidpdx]

I have a leak at the seam of the tank on my old Triumph right about where it meets the seat. I prepped it and used POR on it and the seal lasted for a few years but the leak did come back. One thing that I have heard from from an aircraft mechanic is Green Loctite 609 can be used to seal tiny holes in gas tanks. You create a vacuum on the tank and let it draw in from the outside and then set up. That is the next thing I will try on my tank as I don't look forward to stripping the liner out and starting over. Good luck.

[old biker]

I just got a BIG soldering iron and simply soldered the split with a generous bit of solder using flux .That was years ogo with no probs .
I did ask a welder but he would not touch it since any residual fumes
would just explode with the heat .

[Justin B.]

+1 on the POR15.

[nhmaf]

I'll post an update after it warms up a bit - it is just barely above 0F (-18C) in my garage right now and it is too cold to work in their bare-handed!

[livingdeadhead]

-18 ! wow makes it seem like summer here! its only 6" of snow and 0c!

[livingdeadhead]

i once had an old cd175 (still got one best jap small twin ever) filled it with petrol , the seat had rubbed through the tank , (thin steel) rubbed it down used araldite , repair was still fine when i sold it , funny how some bodges turn out as permanent solutions! a fluke?

[old biker]

Yep snow here in Bolton Greater Manchester (england if your wondering ) 6 inches of it ! but it only snows at +2 degrees centigrade so its WARM here by comparison .....we should grumble .

[Dizerens5]

for a temporary repair to a small split a 50-50 mix of Loctite and non-setting jointing compound works well.

[marcmax]

If you can find this I know it works great. Since it is on the unseen underside and is used to seal fuel tanks it is a natural.

http://www.newpig.com/pig/US/patch-repair-maintenance-7240/pig-epoxy-putty-patch-repair-7459/pig-plug-n-seal-patching-paste-7494/0/20

I have seen it used to seal a leak on a diesel locomotive with fuel in the tank above the level of the leak, press in place, hold with a piece of duct tape until it sets then remove the tape. Done and it is permanent.

I have used it to replace broken off threaded inserts. Mold a blob in place and once it is hardened, drill it and tap it and it is as strong as the original.