DIY! How to Repair Fuel Tank Leak with a Solder for Sheet Metal

tankhanda.jpg How to

Some of the motorcycles that had been left outside for a long time and vintage motorcycles have some troubles such as "gasoline leak" or "smelling gasoline" from the fuel tank. It needs a lot of time and effort to completely repair the fuel tank where such a fuel leak occurs. I tried the "sheet metal soldering'' which is a surprisingly a permanent repair method while providing first aid, so I will deliver its report!!


Fuel may leak from the gap of welding rib parts like an overlap width of the fuel tank and cracks in the butt weld of the sheet metal by vibration. After draining all the fuel and drying the inside of the fuel tank, the flammable gas was released by filling the tap water in the fuel tank, and the paint was peeled off. This time, the old coating film was burned off because the fuel tank had to be repainted.

1. Best soldering iron is 100-200W class


For a soldering iron for wiring repair, the sufficient output can be obtained in a 20-30W (watt) class. On the other hand, it is better to use 100-200W sheet metal solder soldering. This is because the fuel tank has a thick iron plate, which requires a large wattage.

2. Drain all the gasoline before performing the work and dry the inside of the fuel tank


Solder is not only for electrical wiring repair, but there is also a type corresponding to a variety of materials. Since this fuel tank is a steel plate, I used the solder for sheet metal. In addition, a special flux (hydrochloric acid) is used for treating the surface of the iron plate to clean the surface of the fuel tank.


A handy gas burner was also used for removing the paint and to heat the repair area efficiently. When repairing the fuel tank, gasoline and flammable gas must be completely drained from the fuel tank. It is important to prepare in advance.

If hearing "soldering repair", many people may think that it is for electrical wirings repair, but in fact, solder has been used in various situations. The rise of plastic parts has reduced the number of tinplate products, but solder has been used for metallurgy of tin products such as tin toys and tin buckets.

Although it is rare at the present, even in the automotive sheet metal painting industry, there are many examples using solder for concave sheet metal of pre-processing, and for production site of automobile manufacturers in the past, the sheet metal solder was the common.

As the name "sheet metal solder" means, sheet-metal solder uses a special solder and a special flux for preparation. In contrast to solder for electrical repairs, solder for sheet metal has a material mix suitable for heaping, and in the flux for exposed out to the iron plate surface also, the one for sheet metal is used. Since the flux that treats the iron plate surface will rust the coated part after a few minutes of use, useless use with flow down is strictly prohibited. Be careful not to be stuck to other parts.


・Make sure to use a special solder for sheet metal and a special solder flux for sheet metal.
・The affected area must be thoroughly cleaned and then treated iron sheet with flux.
・It is good to apply with a brush so that the flux will not flow out.

3. Drain the gasoline and wash the fuel tank with tap water completely!


Dry the inside of the fuel tank after draining the gasoline, pour a small amount of neutral detergent into the fuel tank and slowly pour tap water to wash the inside of the fuel tank. By filling with tap water, flammable gas inside the fuel tank can also be completely removed. It is better if you remove rust in addition to this work!!


When the tank where the paint was burned off was filled with water and allowed to stand, it was confirmed water drops from the affected part. The rust around the affected area was removed with a wire brush, and flux was applied to the affected area and its surroundings.


This is a welding rib part like an overlap width. After the coating film and dirt around the affected area which leaked were removed particularly well, a flux was applied, and then sheet metal soldering was done. After this solder welding, flush the affected area with hot water and polish it with a stainless brush to thoroughly wash away the flux. The purpose is to prevent the occurrence of rust by flux.

4. Pay attention to the cracks in the sheet metal butt weld


The fuel tank skin (exposed part) mostly has a three-piece structure. The upper surface of the fuel tank is divided into the left and right pieces, and many models are welded at the center. This butt weld ends are often thinned by finishing grinding, and a crack may be formed in this part by vibration.


Solder was poured into the butt portion of the rear end of the fuel tank in which gasoline leakage has occurred, and the mounting portion of the fuel tank cap bracket in which future gas leakage is expected. Since the mounting part of the fuel cap bracket is grooved, thoroughly remove dirt from the inside and blow the air for degreasing.

When restoring a vintage motorcycle, there are many opportunities to paint exterior parts, but in such a case, "grinding before paint" of the gas tank is desired to be done firmly. It was good until it was beautifully finished, In fact, after riding a repaired motorcycle for a while there are many cases "there is a leakage odor of gasoline!" The owner of this fuel tank decided to repaint it because of its gasoline leakage.

The fuel leak was the rear part of the fuel tank where the front part of the seat overlaps, but for the "mounting portion of the fuel tank cap bracket" which is often defective by the fuel tank of the vintage motorcycles was run the molten solder into the groove of the mounting portion and took preventive measures.

The repair procedure is ...

◆ Peel off the paint on the iron plate, and polish the affected area with a wire brush after the surface of the metal appears.
◆ Apply the special flux for sheet metal to the affected area and its surroundings.
◆ When applying, it can be applied cleanly without waste by using a brush.
◆ After firmly warming the affected area by soldering iron, melt and run the solder into the affected area.
◆ If the base material is not heated enough, the solder will not run into, and if it is too heated, the solder will be rounded due to surface tension and it will not run into. It is important to heat the base material in a well-balanced manner.
◆ If the heat will run away due to adding heat by using the soldering iron alone since the iron plate is too thick, it is better to use a gas burner or an industrial heat gun to heat the affected area to provide warming back up.


・If the solder runs smoothly into the affected part, the affected part will pile up by solder for sheet metal.
・If the solder is not piled up, brush the affected area again with a (stainless steel) wire brush to remove any dirt, reapply more flux, and start over again.
・It is a success if the solder is well piled up.