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Discussion Starter #1
I kinda hate myself for asking this but . . .

. . . long story short, a tank I've just had refinished - and it looks great - but it turns out there are two (I think) pinholes somewhere along its underside seam. Obvious signs were, well, obvious really, but the holes themselves are pretty much invisible to the naked eye. Really not sure how they happened; I don't think they're rust 'cos the inside of the tank was spotless. Normally, I'd fill the tank with an Evap-o-rust type solution during the teardown, but this one was so clean that there didn't seem any point. Having said that, it was blasted before it was refinished, so it's possible someone was a little over-enthusiastic with the gun and/or used an unnecessarily coarse media (note to self - don't use that process again).

On the upside, the seam (and so any small/localised external repair) will be very, very hard to see from any angle other than directly underneath the tank; it's recessed away from the outer edges by about two inches. It's also possible that one of the holes is on the inner side of the seam (the bit that faces the frame), which would make it undetectable from almost everywhere.

That said, I've still yet to pinpoint exactly where the holes are. My plan is to let the tank dry out, then very gently apply some air pressure and feel my way around; I'm assuming the holes - and any others(!?!) will make themselves known with air leaks and without the need for me to get any more wet than I did earlier today when I put some fuel in. If it turns out there are many more than I thought plans will change, but in the interim . . .

. . . what fixes (other than welding) are viable in situations like this? I've not come across this particular problem before, so I'm hoping your experiences can fill in some blanks in my knowledge. I've seen folks soldering small holes before but I'm not sure how reliable that fix would be in the longer term. I'm also hoping someone out there has tried JB Weld/two part epoxy and can join in with what they found and whether it's fuel resistant. Again, the rest of the tank was spotless, so I really don't want to use any sort of liner, and I'd prefer not to have to get the tank stripped and repainted again if I can help it.

Thanks in advance.
 

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Generally speaking if there's one pinhole there's a few more that are about to break thru. I would seal the filler hole with a rubber freeze plug and attach a hose to the petcock fitting so you can add low air pressure to the tank while it's submerged in a bucket of water. Low pressure means no more than 15 psi, may be up to 20. That should be enough to find the current leak and probably blow out the real weak spots.
From there it'll be decision time of trying to seal the holes with a gas proof epoxy tank sealer like this Permatex® Fuel Tank Repair, 1 Oz. Epoxy Stick - 84334 followed with a tank sealer like RedKote.
The other option would be a radiator shop that does gas tanks. Not all do so be sure to ask specifically about motorcycle tanks. They'll pressure test the tank, braze the current holes and retest repeating the process until there are no more leaks. Good shops will also use a tank sealer to make the repair permanent.
 

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Like LDR says, more pinholes may be lurking. I've successfully used JBweld and yes it is fuel resistant per the manufacturer. I would identify the pinhole area, rough the surface with 120 or 160 grit paper about a 1/2" circle around the pinhole will do.
Mix up your JB, not the JB Quik, get the regular 2 part JBWeld and add a few drops of acetone. This will thin the epoxy and allow it to penetrate and self level. Block up the tank so that the pinhole faces up and the area is level before applying one little dab at a time. If the JB appears too thick add a drop of acetone and stir it in with a wooden toothpick until it self levels, then leave it to cure.

I've heard tell the entire bottom of a pinholed Honda tank can be reinforced using this method.
 

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If you are careful you can use a liner without affecting the paint. I've used POR-15 and Redkote with great results, some people rave about Caswell but I haven't used it, but Kreem is generally not well thought of. Follow directions to the letter.
 

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Discussion Starter #5
Thank you folks - I feel a little better after reading your contributions. To all those who've voiced caution about the number of holes and the likelihood of there being more than I bargain for, I hear ya. I'll be on the lookout . . .

Jim - great shout with the water submersion test. One of those things that I wasn't in the headspace to think of earlier today but became blindingly obvious when you pointed it out. As far as the pressure side of things goes, I think I'll start out by blowing into the petcock tube, rather than diving straight in with compressed air. I figure that'll limit the damage I can do until I've got the most obvious holes located.

I'm pretty convinced one of the leak spots is around/under a boss on the underside of the tank (there's a boss on each side but only one leaks . . . so far). Looks to me like there's a gap in the welding joint between the boss mount and the tank body that's weakened over time, blasted badly or exploited by corrosion. I'm hoping that's an easy one to deal with.

Alan - thanks for the epoxy tips. I was wondering whether there was any value in trying to apply the epoxy to the inside of the tank through the holes (depending on size) with a very fine needle, letting it set up with the pinhole facing down - essentially trying to create a very small inner liner layer and then inverting the tank and repeating the process to seal the outer. Couldn't hurt I guess.

I'll have a go at submerging the tank tomorrow and I'll report back when I've got a better idea of the extent of the damage.

Meantime, and completely unrelated, I'm re-watching On Any Sunday. Must've been spectacular to watch some of the riding that went on in/through Elsinore from the side of the road. And out of curiosity I thought I'd see what one of the featured riders - Mert Lawwill - was up to these days. Turns out that in addition to bike work, he makes specialised prosthetic hands for cyclists/motorcyclists . . . very cool.
 

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Meantime, and completely unrelated, I'm re-watching On Any Sunday.
Not to hijack, but when you mentioned that it reminded me that Malcolm Smith was backed over by a golf cart - one of two he sponsored in a tournament, no less - about a year ago. I decided to see if I could find out how he's doing since then. Here's a link
 

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You don't need to submerge the tank, just put dish soap & water solution in a squirt bottle, that way you don't have to wrestle with the tank to hold it underwater.
 

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Discussion Starter #8
So there's good news and not-so-good news . . . although the former outweighs the latter.

After trying various detection methods, I could only find one hole. Using air only, I got an idea of what I was looking at. The soapy water method didn't go so well, so to be absolutely sure I did a submersion test. Here's what I'm going to be working with:

CA77 tank pinhole


One tiny, but very clean pinhole. I've had a dig about with some dental tool-type pokey things, and there's no weakness around it - best bit being it's not rusty. I still suspect it was some overly aggressive/sharp blast media that caused the puncture.

The not-so-good is that in carrying out the various tests, I managed to wreck the finish. The tank was resting upside down on a towel and despite my best efforts to make sure it was empty of fuel, there were still some traces that leaked out. They soaked into the towel, and when I picked the tank up after five minutes or so, the finish on the areas that had been resting on the towel had softened; that allowed fibres from the towel to adhere to it. And no, it's not going to polish out . . . I tried. Knickers.

All things considered it could have been a lot worse. I'll strip the rest of the tank with thinners/paint stripper, get the hole patched, make sure there aren't any others and go around again. And if that's all I have to deal with, I can't really complain too much. Lesson learned for the next one (which is currently sat in a box . . . ).

Thanks again all.
 

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I would flow some solder into the holes, brazing works well also but paint doesn't like to stick to brass , sticks better to lead-based solder. Also,you're less likely to ignite gas fumes with a soldering iron than with a torch.
 

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Given the location of the holes I'll recommend using a tank sealer like RedKote. The seam area where they're located is a low spot of the tank structure and is prone to collecting sediment, water, etc. causing rust out.
After you repaint the tank and decide on decals, pinstriping, etc I'll suggest shooting the tank with Spray Maxx 2K. It's and epoxy clear coat that's pretty much impervious to chemicals and fuels. Comes in matte, satin and high gloss.
 

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Discussion Starter #12
The second 'hole' is an optical illusion. It's an imperfection in the steel that's got a tiny trace of black paint residue in it. Nevertheless, I'll touch it up along with any other marks I uncover.

Mike - I was thinking solder, but also debating whether to use silver solder (I've got some somewhere). I'll probably apply flux to the outside and do the same process as I mentioned with the epoxy of using an ultra fine needle to feed small amounts into the hole (I've got some 0.025mm medial needles knocking around that are flexible). I'd like to get a decent amount of solder behind the hole and around that area and with any luck the flux will draw it in. I've also got some lead tin bar that's s'posed to be good for low heat applications, but I've never had a great deal of luck with getting it to stay where I want it to.

Jim - I hear you on the tank sealer, but I'm still reluctant to go that route just yet. As I mentioned, the tank is still very clean inside despite being around 55 years old. I realise newer fuels contain additives that weren't used when this thing was originally sold, but I'm pretty good at keeping the tanks topped off and the fuels treated with stabilizers that should minimise the long term effects of stuff like ethanol. I've also had to deal with a couple of tanks where the sealer has failed/gone bad over time, and refinishing the tank will be less work than fixing that mess. I'll see how I get on with the soldering option . . .
 
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