Kohler 12hp gas tank leaks
 

So, when I bought this old Cub 123, it had a leaky gas tank. Seemed to be the weld between the bung and the tank body, and it appeared the PO had tried fixing it a few times with epoxy, to no avail. I picked up a used/vintage steel tank at a flea market, and all was good... for about 10 months. Now my new tank seems to be leaking, and although I haven't pulled it off the machine for a full inspection yet, it appears it might be from the same area.

I'm festidious about the fitting of the tank straps, and ensuring the soft webbing is properly placed between the tank mount and the tank, so I don't think it rubbed thru there. Seems to me, there may be a flaw in these tanks. Has anyone else had similar experience?

Mine's got the original glass (clear plastic?) fuel bowl on the aluminum casting hanging directly from the tank bung, and a steel line running from that to the carb. The tank is all steel, with a square flange and four spot welds on the bung.

Fred

They make some stuff called Kream for motorcycle gas tanks. Awesome stuff. I used it on an old Kawasaki gas tank that was rotted to death and no more leaks.

The bung is soldered in, not welded, and there is no flaw- these things are 40+ years old; you can't expect things to last forever. This is probably one of three things:

-The solder joint for the bung cracked and is leaking
-The PO left off some of the padding and the mount bracket wore it thin, which then cracked
-Water in the gas over time rusted pinholes in the tank that may be invisible (or nearly so) to the naked eye

Cool. I'll have ot check that out as a back-up option. Thanks!

Thanks, Matt. Both tanks appeared to be clean / no signs of rust. I'd be surprised if the rust is so bad as to have gone thru, while being completely invisible to the naked eye, but I suppose anything is possible.

First tank failed at the bung, without question. Not sure about the second, because I haven't removed it yet, but it appears to be the same. Pretty sure it's not an issue of rub-thru, as this tank was pristine when I installed it last year, and I've checked on the webbing at the mount many times.

I've brazed new bungs into fuel tanks before, but it's something I hate doing. Always scares the piss out of me, no matter how well I rinse and clean the tank first. Something about putting fire to a metal tank once containing gasoline...

Anyone expert in soldering these steel tanks, please speak up! Interested in what flux and solder you used. I just moved, so I don't have the full shop set back up yet, but I do have acetylene, mapp, and oxy-acetylene set up already. I also have a MIG welder, but no gas bottle at the moment, rigged with flux core for outdoor welding. If the old bung is truly soldered, it should not be too much trouble to remove, clean, and re-solder.

Thanks!

I have found sometimes bungs are spot welded into a tank,and also soldered so they are leakproof.
They are spot welded so when over tightning a fitting, the softer solder joint is not twisted allowing the threaded fitting to fall off,
and/or vibration does not fracture the solder, also for assembly purposes.
I wash out tanks well with hot tide laundry soap. then solder or braze/silver solder as needed.
if a fitting is soldered do not try to weld it or braze it,-- resolder, using a large soldering copper, is the best procedure.
If it is brazed you can silver solder or rebraze it.
An once of Muratic acid diluted with snipped pieces of a zinc jar lid is the best cleaning solution for soldering.
Heat the fitting enough to cause it to soften/bubble the solder and brush in the acid to allow a good sweat joint, not a "mudded" glob of solder
Done right, the solder is sucked right into the joint like a sponge taking water.

Thanks, George! Since I don't have muriatic acid handy, can I use good old fashioned plumber's paste flux? I'm talking about the old Rosin stuff, not the modern water soluable, although I do have both.

Thanks again.

Yes you can use that.
I have a old can of soldering paste for clean jobs,
but if things are dirty, cut muratic acid is the only thing that will clean them up to allow a good sweat joint.
You must cut it with zinc, a jar lid works well,do not dilute it with water.
Small snippings of the zinc are added till the acid quits eating them, then it is diluted properly to do a great job of cleaning material for soldering
This past winter I repaired a 1915 honey comb radiator, @ that age, it needed a good cleaning acid.
A soldering paste was just not up to the job.

I hope you're passing this knowledge onto someone, ol'George! You definitely know your way around a torch and solder better than me.

My grandfather was a similar wealth of obscure knowledge, as an old-school plumber, who also apprenticed as a blacksmith. I picked up what I could from him as a kid, but too much of it was still beyond my years when he passed away.

Do yourself a favor and wash the tank with soap and water 3 or 4 times before putting the fire too it. I had to do mine and took a long stick with fire on the end to flush out gas fumes, took three times before they were escaped, the tank literally "popped" four feet each time with what looked like flame from a jet engine out of both the in and out holes. Just a little safety percaution...

I used silver solder to fix my leaky tank. It leaking at the same spot. I rinsed it with soapy water a few times. I also used a trick recommended form a mechanic friend. I piped the exhaust from my truck into the tank to help displace oxygen and gas fumes with good old CO2 and CO. Not sure if that helped or not, but I didn't blow up and the tank stopped leaking.

That's a nifty idea, never thought about it. A buddy of mine said a piece of dry ice would do the same, so you could do that if you drive one of those electric cars and can't get exhaust fumes....

Yep, if you're one of the nine people who bought a Chevy Volt, you're out of luck! :-)

John

I used my '70 F350 exhaust. Good old pre emissions exhaust.

Sounds like we came from similar families
Dad was born just after the turn of the century; he learned it from his dad as
they were plumbers/tinners, having their own business.
In those days you learned how to wipe a lead joint as most water pipes were
made of LEAD.
Funny how we learned that lead is bad for our brains after so many years of using it, but I'll not go there.
The young people today are just not taught old school skilled trades.
When chit breaks, somebody has to be able to improvise/repair as not all things are computer driven.
The schools in my area don’t even have/teach shop classes now a days, how sad.
With all the good/high paying jobs gone from this country, where are folks going to get the $$ to pay someone to fix everything?
I have experienced recent engineering graduates that don’t have the least bit of mechanical ability; you can’t learn that in a book.
It has to start @ home or at least in high school.

When I left high school we had to be able to proficiently operate a lathe, mill (Bridgeport), shaper, & weld,--- acetylene/oxy as well as arc.
We even did some aluminum sand casting.
2 days after high school graduation, I had a job in the auto industry going on to apprentice school.
Today they are in a pickle, because all us old guys are retired and we were not able to apprentice young fellows under us.
The only salvation I see is the world wide web for advice/help just like here @ OCC
Sorry for the long winded post

Well, because they can be had for $20 - $40 on ebay, I just bought another used steel tank. It's the quickest way to get back up and running this week. I'll be doing the solder repair on the old tank, so it's sitting on a shelf ready to go, when the one I just bought (my third!) innevitably fails.

My proceedure for soldering tanks in the past was to soak and wash out several times during the course of a week (I usually only get to do repair work on weekends anyway) with water and detergent. I'd also do the flame-out test from the safest possible distance, but never fun with a 10 - 20 gallon auto tank.

More recently, an old-timer at work had taught me the exhaust trick. I like the idea, but have never tried it myself. Not sure how I'd "pipe" the exhaust from my pickup to the tank.

Thanks for the thoughts, ol'George. I agree with most of it, but it's just the way the world works today. Thankfully, there still seem to be a lot of guys who know how to turn a wrench, whether they learned it in school or not. Similarly, I've seen some real ugly repair work done by folks a generation older than me, who went thru the obligatory shop class program of the time. I'm not sure all those high school students taking shop in the 1960's absorbed what was given to them, any more than many teenagers today absorb the calculus taught to them. No matter what the future holds, I assume there will always be a self-sufficient few (and then the rest), as has been the case in every generation.

I used the hose from my shop vac.

Now I don't recommend this, but I have soldered tanks with gas in them.:bigeyes:
When using a soldering copper, there is no flame to cause an ignition,
but that is me.
This past winter I did an extensive gas tank solder repair on a '52 M38 jeep for a 81 year old Korean vet that he was restoring.
It was done with a soldering copper and little washout, but man that thing had more rust holes than a old model T muffler buried in the dirt for 50 years.
But it's best to wash tanks out and I also have flashed tanks by passing a torch over/in the opening, just to make sure they are clean when doing a welding job.
I remember modifying a sportster tank for a guy, many years ago that had some gas residue in a seam and after a little welding, it gave a whoosssh, and got my attention, Ha,LOL-- no harm done just a attention getter.
For soldering, I will not use any kind of torch, just an appropriate sized copper.
Way better and no chance to overheat and burn the metal causing you to start over and it enables you to bridge many rust holes easily.
Radiators are the same situation no torch used, it's to easy to overheat.
Now on body leading, I do use a natural gas torch and compressed air to paddle the lead, but I like to use the copper to tin it first,-- ya it's slower and more costly but it's old skool and I'm comfortable with doing it that way.

what kind of sized heated copper would you use to have enough thermal mass to solder a tank? Do you heat it with gas, or...?

John (who has some old vintage soldering "coppers")

[QUOTE=jbrewer;138549]what kind of sized heated copper would you use to have enough thermal mass to solder a tank? Do you heat it with gas, or...?

John (who has some old vintage soldering "coppers")[/QUOTE

The bigger one is maybe 1-1/2 sq 2-3" long I heat it with Nat gas burner I built for it, but you can use any heat source,-- propane torch, oxy/acc,
blow torch, plumbers furnace etc.
I would think a at least a 1x1" would work, they have numbers a #1 or 2 will work well, but most old ones the numbers are long gone from drawing them out, as they wear.
The bigger ones hold the heat longer.
When heating them, don't go to hot or you will loose the "tin" on the tip. if you do, just plunge it in paste or acid and quickly re tin with solder, it's important to keep the "tin on the tip as this is where the heat transfer takes place!
It takes practice but once learned it is really easy to use.
Now if you are sweating copper plumbing a instant-lite propane torch is the way to go.

My dad has one of those big coppers...we fixed one of my tanks that way years ago. It worked great.

can I get some more info on that.

I got an old Yamaha dirt bike that needs some attention.

bump... I really need to fix my gas tank.

It doesn't take flame to ignite gas fumes... just any object beyond ignition temperature.

I have an old set of very large soldering irons, one at least 1.25" in diameter. About the size of a soldering copper, and I've used them for soldering copper roof and window flashing. I suppose I could try it for gas tank repair, although I had sort of set my mind on doing it with a torch.

New guy here, the gas tank on my 100 needs a liner as well. I have found a few different fuel tank sealer/liner kits:

Eastwood, $34 shipped on ebay:
http://www.eastwood.com/gas-tank-sealer-kits.html

POR-15, $40 shipped on amazon:
http://www.por15.com/CYCLE-TANK-REPA...ductinfo/CTRK/

Kreem, $41 shipped on amazon:
http://www.bikebandit.com/kreem-fuel...iner-combo-pak

Which one is the best?