[bmetz99]

Bondo will shrink and fall out.

Only if you do it wrong. At least that's been my experience in doing body and paint work on cars and motorcycles for the last 35 years.

 

[bmetz99]

Your tank is a good candidate for a Bondo-based repair. If the dents were shallow and not on an area with a sharp bend I'd recommend trying paintless dent removal (where they alternate heating the dent and chilling it with liquid nitrogen to get the dent to shrink and pop out) but you've got some damage that won't respond to that kind of effort.

You don't want to put more than a 1/4" thick layer of Bondo on- that means pulling the dents that are more than 1/4" deep. I've had good success with drilling a small hole or a series of small holes in the dented area, then screwing a sheet metal screw into the hole and pulling the dented area out with a pair of Vise Grips. You have to be careful to not pull the metal out past where it originally sat (don't make a high spot). You must then close up the holes by welding or brazing them.

Grind off the paint into the smooth area surrounding the dent, then mix your Bondo and lay it down with a piece of flexible plastic- a piece cut from a coffee can lid works great. The idea is to fill the dent so that it's flush with the surrounding area. This may take more than one application. Make the Bondo as smooth as possible, and shape it with a coarse wood rasp while it's still somewhat soft. If you wait until it hardens completely you'll have to do a LOT more work. Again, work one area at a time, work quickly, and build up to meet the surrounding area. Too many people try to fill all the dents at once and end up with a hardened mess that's a bear to work with. Rough things in with the first layer, then make the Bondo smooth and blended with the surrounding area with the second or third application

Once the Bondo is blended, sand it as smooth as possible with a block sander. Use glazing putty to fill in all the micro-fine scratches and defects, and again block sand with 400 grit wet-or-dry paper. From there you'll want to rough up the entire tank with 400 grit wet-or-dry (wet!) and then prime, sand, and paint.

You can get a good color match with the Color-Rite spray cans if you use a white or grey primer and build the base color coat until it matches the other pieces on your bike, then build the metal flake/pearlescent coats. From there I'd take it to a professional painter and have them clear coat it. It'll run you another $100+ but you'll end up with a factory-like finish that'll stand up to gasoline (important on a tank) and last for many years. At least that's what has worked for me.