Petrol leak

[ste]

Anyone have a petrol leak from under the rear tank mount on a TS? We did a leak check before it was painted but is now dribbling up as I ride, between the mount and the tank.
Is it possible just nipping up the screws? I would've thought no petrol should be getting out there?

[oily bloke]

Hi,
I had a similar problem on my EW. Inside the tank (assuming they are assembled in a similar way) there are plates soldered across the inside of the tank with captive nuts which have a lead 'top hat' over the nut to prevent leakage. I can see a number of possibilities. The top hat has been pushed up by using too long a bolt, cracking the lead, or twisted due to gunk in the threads or an incorrect threaded bolt being used. The plate has been lifted for the same reason or corrosion has broached the plate/tank join. If the tank has been lined internally then it is possible that the fuel is getting past the liner due to poor application and is finding its way to the weakest point. Think of flat roof leak where the leak can be anywhere on the roof but finds its way to a weak spot a significant distance away from the faulty area.
Pressure testing OK is a good indicator but can mask leaks where the fuel has found a path behind the liner as the pressure can push the liner against the tank making the result look OK.
The tank mounts may be out of true causing stresses on the tank. The solder used on these tanks is good but seems to be age hardened making it less pliable and more prone to stress and vibration fractures.
Hope that helps
Andy

[eddie]

Hi,
     The problem may be exaggerated by the tank getting pressurised due to the breather being blocked. On most 2 3/4 tanks the breather is just a shallow cut down the filler neck threads and a small hole just below the rim. This hole can easily get blocked with dirt or paint (after a respray).

Regards,
              Eddie.

[Chris]

Hi ste
Inside the tank the suspension is taken care of by a bronze casting soldered to the inside of the top panel of the tank on the TS and similar suspended petrol tank models. This casting has two integral bosses which are drilled and tapped to take the screws. It is quite difficult to solder the casting to the tank as the difference in material volume and sections necessitates a good amount of heat which can in turn cause distortion of the top surface of the tank. If the solder joint is not good then petrol can leak between the casting and the top surface of the tank emerging through the holes in the top of the tank through which the screws enter. A more likely cause of leakage is if at some time the tapped holes for the screws have been stripped and drilled and tapped oversize. If the drilling has been over enthusiastic and penetrated the bosses of the suspension casting this will permit leakage. It is also possible that the casting has developed cracks just due to age or shock loading of a full tank bouncing over a rough surface when tightening of the screws could have opened the cracks.. Without stripping the tank for fundamental repairs the simplest and most effective cure is lining the tank with one of the advertised tank sealing products. Having said all this it is much less likely to be a problem with suspended tanks on models like the TS as it is not common for the tank to be so full that petrol is in long term contact with the inside top of the tank. I have this problem currently with two tanks that are secured to the frame brackets from underneath but then you have  petrol always over the internal castings with considerable pressure from the head of petrol above it. Chris.   

[ste]

Thanks guys for your replies. Is there a quick fix without tanking the tank off and internal work?

[eddie]

Ste,
      Assuming there are no hairline cracks around the mounting boss, a good smear of red Hermetite on the threads of the mounting screw should stop any leakage up the threads or between the skin and mounting boss (providing the screw doesn't bottom out - in which case the skin wont be pinched up).

Regards,
              Eddie.