Brazing fuel tank and fork ears

When I took of some paint and rust I discovered two pinholes in the fuel tank. The rest of the tank was in good condition. It's just the part where the seat meets the tank that was rusted. Same thing with one of the fork ears, 3 small holes on the inside.

Pinholes in Yamaha Fuel tank

Time for some brazing!
I used brazing rods containing 5% silver.
Melting point of those brazing rods is around 650° Celcius, melting point of mild steel is around 1450°-1550° Celcius. The difference with welding is that the braze alloy and steel won't fuse/melt together but will bond like glue, the braze alloy works like a filler. You could also try to weld it but I find brazing easier and the change of warping is less than with welding. I used a simple and cheap propane torch, as long a you braze pinholes it will work.

Brazing rod, propane torch and flux

Before you start brazing, make sure the tank is completely empty. My fuel tank has been empty for 4 months or so, so I blew some compressed air through it to get rid of the last fumes.

First you have to heat the area you want to braze till it's red hot. Then add some brazing flux, let it turn brownish and press the rod on the hot spot. The trick is to melt the brazing rod with the heat of the part you want to braze instead of melting it with the torch flame.

Brazing pinholes Fuel tank Yamaha LS3

Brazed pinholes Fuel tank Yamaha LS3

Brazed holes lamp ear front fork

After brazing the holes I sanded it back with 80-120-240-360 grit.
The rest of the rust pits I'll fill with JB Weld or some other filler.

Brazed pinholes fuel tank Yamaha LS3 1972

Brazing holes in lamp ear  front fork Yamaha LS3

To make sure the tank wasn't leaking anymore, I filled it with water and waited for an hour or so. No leaks!

Leak test brazed fuel tank Yamaha

After the test I used a paint stripper (on low!!) to get rid of the last bits of water drops in the fuel tank.

Drying Fuel tank Yamaha LS3 1972

There was also a nasty dent in the exhaust. As trhe dent wasn't too big I filled it with silver solder. Make sure it's thick enough so when you sand it back it will be smooth and flush with the exhaust.

Dented Exhaust Yamaha LS3

Brazing dent in exhaust Yamaha LS3

Brazed dent in exhaust Yamaha LS3

Smoking hot

Brazed and sanded 

Next thing to do is strip back the fuel tank to bare metal for painting.