The tank of my 1948 ZB32 has leaking petrol since not long after I bought it just over 4 years ago. I found that it had been bodged up with Petro Patch or some other epoxy putty at the front just behind the steering head where it bolts to the tank. A design asking for trouble.
Over the past three years I have tried to alleviate this by scrapeing out any putty that was detaching, cleaning the surfaces and applying more but it never lasted more than a few months before it was leaking again. I got in the habit of never filling the tank more than ½ full.
This year I got fed up of it and decided something had to be done. I was reluctant to have it welded because this would almost certainly have damaged the chrome and possibly the paintwork, the tank is chrome plated with silver panels at top and sides, so I decided to solder it.
Since I would need a gas flame to get sufficient heat I was going to have to de-gas the tank first which was a worry. I went about it, after completely emptying the tank and leaving it for a few days with the cap off, by squirting in a good dose of washing up liquid (I used "Elbow Grease" which claims to be a good degreaser) followed by a kettle of boiling water and giving the tank a thorough shaking. The steam produced certainly showed up the leaks. After emptying I ran a hose through the tank for a good 5 minutes. I then emptied the water out. There was only the very faintest smell of fuel from the filler now. So I carefully at arms length held a lighter to it. I'm happy to say that nothing happened, not even a pop. I did this outside.
Happy that it was now safe to use a flame I went about soldering up the leaky section. Although there was an obvious hole at the top RH side the seam was in fact leaking out most of the way across the seam. I checked at various stages by having the filler cap in place with the vent taped over and applying pressure through the fuel tap union with my small portable compressor. A little soapy water over the mended area showed any remaining leaks. I'm now happy with result and hope that it is more permanent than the epoxy putty.
Incidentally, for others with a rigid or plunger frame with this tank fitting. I have a lenght of pipe insulation foam along the top rail of the frame which helps hugely in preventing the tank from vibrating. At the rear are 2 isolating rubber mounts and at the front the bolt has an acorn nut so that when fully tightened it doesn't grip the tank lugs. I've also have modified rubber grommets in the holes that the bolt goes through but they are a very tight fit.
Below is picture of the repair and one of the sort of rear mounts fitted.
Hi,
These rigidly mounted tanks can be prone to cracked joints. On the plunger frame A7/A10, BSA ended up using a rubber bush at the rear of the tank and a bush in the frame at the front.
On my wife's A10 is has the tank with the rear bush but no bush in the frame. I found that the front bolt had to be very tight to stop any vibration but ultimately I used POR 15 tank sealant and it has been good for many thousands of miles. It is not cheap but the kit contains all the rust remover/killer and metal prep. needed. There is enough sealant to do two tanks so either do two of your own or buddy up with someone to save costs.
It is also important to fit any cross brace under the tank to prevent any 'flapping' of the tank.
Dave.
I've used POR15 in the past on a Ducati tank with good results but in this case I preferred to use something more solid and I'm less keen on using sealants with the current ethanol fuels although I believe the POR15 has now been changed to make it ethanol resistant. The trouble with sealants is once the are in you can't get them out again and if they go wrong you are in trouble.
The tanks on the singles are a bit different from the twins. There is no cross brace nor any means of adding one. The front has no rubbers at all yet the Gold Star versions had a sleeved rubber bush in each front lug. I don't know why the rest of the singles didn't get this as they are all subject to the same vibration issues. My rubber pipe insulation over the top frame tube cuts down in the vibration hugely.
Hi,
The extra support from the rubber on the frame tube is a good idea.
The tank I used the POR15 in has had a lot of E5 and E10 through it with no issues but a 'belt and braces' approach is worthwhile.
Coincidently, I am about to fit the smaller A7/A10 tank which does not have the brace so the rubber on the frame tube will definitely be explored.
Dave.
If you can get the solder to stick I think this is a good repair, I've done it to rear axle cases and oil tanks. You can also run an exhaust into the tank so its full of inert gas. Be careful with boiling water and petrol, you can create a flammable vapour mix of petrol fumes and steam. There's been a couple of nasty accidents with people using steam clearers. When I did a car petrol tank I filled the tank with water to about an inch below there I was working. But this method means you have to put more heat in and risk distortion, OK on a car tank but not so good on a bike one.
I've seen a (real, pre-dates AI) video of a guy in Mongolia welding a fuel tank but putting a rag in the filler and lighting it while he's working. There's some sense to this as its stopping the vapour build up.
I did the boiling water outside, well aware from any naked flames or sparks. I used resin cored lead solder and "killed spirits" as an additional flux. I had no problems getting the slider to stick.
I can see the thinking behind the burning rag in the filler but it's not something I'd like to try. ::)