Hi all,

My 1984 K100 has been up and running for a month or more now - after finally getting it registered in the UK. It's running well, but there is a small leak from the fuel tank (front bottom left-hand side before the lower seam).

This is a leak that had been repaired before.

Should I repair this from inside or out?

What is the best method/material for the job?

Will post some pics - there's an odd fairing on my bike! Wonder if anyone else has one.

Best,
Neal

Hey Neal, Hi!

My 88 was repaired with JB weld on both sides when I bought it. It looked to have been on there a long time, since it had been painted over. I replaced my tank but who know how long it would have lasted... A good welder can fix it easily with a TIG machine also, once it's cleaned out. I don't know about sealing the inside. Maybe someone else can say how that works.

Luck!
Steve

Hi Neal,
There are two ways to fix this, internally and externally. The internal fix uses a resin which coats the whole tank interior and works really well. My pal's Suzuki Intruder tank rusted out and had a big hole. A patch was fitted and brazed in and the tank treated and is now perfect again plus protected from further problems. My K bike tank had a small spot where it was getting damp with petrol and I used Permatex kneadable petrol tank sealer. I took the tank off, cleaned the area and with the tank positioned so there was no pressure pressed a blob into place firmly. It sets very hard and has not leaked at all since. I know several people who have used that and a similar Loctite product.
Regards,
K-BIKE

Great thank you!
Neal

Hi neal

Just discovered I had a 3mm hole in the tank immediately underneath where the fuel pump sits just inside the seam. After reading this thread and others on flyingbrick website and general google search on various products available went with the Permatex GTR 1 Gas Tank and Radiator Repair kit. $8. Only used 10mm piece off the roll. They claim it sets hard within 5 minutes and can be drilled machined etc in 2 hrs is pretty accurate too as it set hard as a rock. The Full cure time indicated is 24hrs and unlike some of the other products claimed suitable it is impervious to fuel deisel oils detergents etc. not merely resistant.

I'm in the UK. I've repaired my  fuel K100 tank with putty twice. First time lasted 5 years. Second time 5 months. Second time I cleaned the area scrupulously. I used Granville repair putty. I have been told that the latest petrol additives in the UK are much more reactive and aggressive. I know this as my fibreglass tank on my old BSA became very porous a few back after 40 years of ownership! So does anyone know of a putty that will work for a decent time with current petrol? (None of the ads seem to mention this)

The following has been around for years (notsuitabel for plastic or fibreglass tanks though)

https://www.amazon.co.uk/Por-15-Sealer-Repair-prevention-236ml/dp/B00APFN1YM

Supposed to be o.k. for use with high ethanol fuel.

Mike

Why not try brazing? 
https://www.ebay.com/itm/10Pcs-1-4mm-500mm-Aluminum-Low-Temperature-Repair-Welding-Soldering-Brazing-Rod/332908353005?epid=912007244&hash=item4d82e255ed:g:0gUAAOSwjyBcdhoZ

Thank you both. I hadn't thought of the low temp brazing option, although have come across it years back. Never done it tho'~. I'll strip the tank down and decide when its bare, cheers

Hi Neal You don't say if the tank is Alloy or steel but i would think Allo on this year.low temp Alloy welding/brazing is a first class repair. For safety rig up a steam feed to the inside of the tank to prevent igniting of fumes,simple is best ie kettle with rubber tubing works well.
N/B good videos on utube

Just remembered Liquid Metal developed for the military impervious to petrol etc no heat required flows well wort a try

thanks for all ideas but I needed to use my bike so tried a last attempt fix with a putty. I used PC7 - it took 3 days to cure and I read somewhere that slower cure meant more inert epoxy.. (maybe rubbish). Only 4 months but no leak yet... time will tell

ps -tank is alloy

downssm wrote:Hey Neal, Hi!

  My 88 was repaired with JB weld on both sides when I bought it. It looked to have been on there a long time, since it had been painted over. I replaced my tank but who know how long it would have lasted... A good welder can fix it easily with a TIG machine also, once it's cleaned out.  I don't know about sealing the inside. Maybe someone else can say how that works.

 Luck!
  Steve

I'd be doubtful that welding would be successful on a rotted through tank since the metal is very likely thin and weak in the surrounding area. It's a bit like welding a rusty exhaust pipe. If you can add a patch to some sound material a bit further it can work but filling will just melt more holes.

Also ali has high thermal retraction on cooling so the repair pulls in and is never clean. You could get away with welding inside the line of the seam where it would be less visible but it's tricky on ali tanks. 

I have K100 tank which has corroded through in several places due to water infiltration resting in the bottom of the tank. I have to assume that the well on both sides is pretty thin and  weak in multiple places. I will try to find a fluid resin suggested here by some.

The challenge is how to clean the inaccessible metal inside the tank. First port of call is jet cleaner but I'd like some abrasive solution to remove any oxide and have clean sound metal. At the same time I don't want any kind of sand or carborumdum dust hanging around. Well may be course gained quartz sand ... ?

The trouble is these tanks really don't drain well because of the deep ring for the filler cap.

Any ideas on chemically reducing the oxide layer with an acid rinse before applying these products?

Any tricks to share?

Mine went I had it tig welded but it was unsuccessful, I ended up using chemical Metal epoxy

Beamer wrote: The trouble is these tanks really don't drain well because of the deep ring for the filler cap.

Would you please explain how a ring for the filler cap affects drainage of the tank? How much fuel is left over after emptying that couldn't be sopped up with an old sock?

Laitch wrote:

Beamer wrote: The trouble is these tanks really don't drain well because of the deep ring for the filler cap.

Would you please explain how a ring for the filler cap affects drainage of the tank? How much fuel is left over after emptying that couldn't be sopped up with an old sock?

I was not discussing removing fuel.

Beamer wrote:I was not discussing removing fuel.

I enjoy a cryptic answer as much as the next person. 

I didn't read that you were discussing drainage until the post to which I responded. That's why I asked. Drainage and filler cap were in the same sentence. Previously, you seemed to be discussing fuel separation leading to water residing along the lower seams of the tank. How does the filler cap opening contribute to all this.

me wrote:The challenge is how to clean the inaccessible metal inside the tank. First port of call is jet cleaner but I'd like some abrasive solution to remove any oxide and have clean sound metal. At the same time I don't want any kind of sand or carborumdum dust hanging around. Well may be course gained quartz sand ... ?

The trouble is these tanks really don't drain well because of the deep ring for the filler cap.

It was in the post you replied to, on the previous line!  If you don't read what is there, I can understand you finding it "cryptic". Just don't blame me or get snarky.

Beamer wrote: If you don't read what is there, I can understand you finding it "cryptic". Just don't blame me or get snarky.

Are you trying to corner the market on snarkiness, or keep up the pace, Beamer?     Regardless, my interpreter tells me you might be referring to removing the filings, so I'll go with that.

Fine, so now we've established that the deep ring supporting the sunken filler cap impedes cleaning of the fuel tank, hopefully we can get this thread back on the subject of repairing leaks.

White Vinegar strong enough to remove reside without risk of damage.You can make several Thingamagigs to scrub about with.  Iwould look at repairing the tank Inside and Outside, Belt and braces moto

Beamer wrote:. . . we've established that the deep ring supporting the sunken filler cap impedes cleaning of the fuel tank . . .

You really should take sole credit for establishing that. 

I agree with Moriarti. Also, the tank bodies seem thin enough that abrasion of them could become problematic. Once tanks have been cleaned,  POR-15 has been used successfully by several Brick owners.

moriarti wrote:White Vinegar strong enough to remove reside without risk of damage.You can make several Thingamagigs to scrub about with.  Iwould look at repairing the tank Inside and Outside, Belt and braces moto

I was wondering about some kind of mild acid wash to remove the oxide layer but that needs to be based on science, it could end up worse. Abrasion seems better but with all the baffles, tubes and other structures inside these tanks, I don't see that being very practicable for much of the area.

Mild acid wash!! That's vinegar. Should you require a scientific 100% guarantee, Send the tank to Professional tank repairer  company.

moriarti wrote:Mild acid wash!! That's vinegar. Should you require a scientific 100% guarantee, Send the tank to Professional tank repairer  company.

Yes, thanks, I am aware that vinegar is A weak acid. That does not mean it is the best choice or suitable for aluminium or even that acid is the best option.

If I could rely on anyone who called himself "professional" to deliver 100% guarantees, I would not need to fix my own bikes and would not be wasting my time on forums. 

Seems like I subscribed to the smart reply thread by accident.

Vinegar does a good job of gently cleaning the inside of fuel tanks. I have successfully used vinegar in three tanks to clean them out. There are at least 30 tanks that have been cleaned with white vinegar and documented on this and the Motobrick forums. A search will reveal a number of them.

Please know I am not being snarky with this post, just politely offering some of my experience.

many thanks .75 , that's useful. 

I think the question is what are we trying to remove?  General gunk and stale petrol vinegar is probable a good solution.

The thing here it for the corrosion there will be fluffy white aluminium oxide. For the resin to bond well I think that probably needs either etching way chemically or a bit of ( gentle ) mechanical abrasion to stick to clean metal.

I get the gut feeling swilling course quartz sand back and forth with water would be sufficiently abrasive, if I could clean it out well enough afterwards.

Maybe a water capable vacuum cleaner would suck it out to get around problem with the rim.

Moriati's suggestion of sealing both in and out side sounds a wise precaution, at least inside the folded rim.

Easy Beamer, nobody's time is wasted on our forum, we ask and reply as best we can,sometimes with tong  in cheek humour, Maintaining/repairing our bikes is a way of life and if we can help each other that's a bonus  I F YOUR TANK IS A EARLY ONE WITH SINGLE BOLT MOUNT. Then i have a spare without any damage/repairs /leaks.If this of use PM me for price and shipping costs.   Happy to help.

Many thanks for that offer.  I'll chew it over. I'm getting more inclined to giving this one the bullet. It's probably more cost/trouble than it's worth to end up with a damaged/repaired tank. 
If I was a bit nearer, I'd snap it up.