Tank Dents

After setting over 10 years I'm bringing my old '82 KZ1000 back to life. It has two dents in the tank. One is where the front screw on the "KAWASAKI" is attached. The other is right below it. I had to drill out the stripped screw where the dent is also.
Best way to pop the dents back out?
How to chase threads for screw?

From what I'm reading the screw is a 3mm x .6. therefore that would be the same size tap correct?
Ken

Take the tank off, wash it out COMPLETELY and then over to any decent body shop and have them spot weld a few appropriate "dent puller" studs and yank on it.. snip them off, grind the nibs down and start with some good filler.

There's some videos on you tube about dents using dry ice,heat, even peanut butter.
Steve

The peanut butter was an april fools joke from a few years ago. Don't actually try it

As missionkz mentioned, the first step before any techniques requiring heat is to clean the tank thoroughly of any remaining fuel. Gas fumes are more explosive than liquid. I've had welders insist the tank remain filled with water before they would touch them.
For that particular area, you may be able to get a wood stake thru the filler neck. Cut the stake at a 45 on the end. Heat the area starting at the outer perimeter of the dent. Use the center hump in the tank for leverage sliding the butt end of the stake across the dent to push it out.
I've never tried it on a gas tank, but this has worked on some crushed Ti head pipes. Get expansion plugs for the filler and petcock holes. Fill the tank with water completely and seal it. Place in a freezer. Just like frozen water pipes burst, the ice will expand and force out the weakest point. Hopefully the dent. You have to watch this closely because the next weakest point is the tank's weld seams.
A similar technique is to install a schrader (tire) valve in the filler neck expansion plug. Heat the dent area and use compressed air. This allows you to control the pressure and area. Start with minimal air pressure and work up. Also keep in mind that applying heat will raise the air pressure. Just like the freezer method, the risk is bursting the tank at the seams. I know a guy who made a pretty good living repairing crushed/dented 2-stroke expansion chambers with this technique.

As I remember it one method was to use liquid air for cleaning computers to freeze the area and watched as the dent poped out on it's own.
Steve

Ive tried that.You hold the can upside down and it sprays something very cold (Im sure someone on here can explain what). In theory,shrinking the metal,which,if its under tension will spring back into original shape. Didnt work for me
though. I think it depends on what sort of dents you have.

I have a spare Z1 tank I had painted. I used Bondo to fill a dent made by the fork in the wreck. I spent a lot of hours sanding and painting, got it to the same purplish blue like my helmet, clear coated it, god it looked good. Must have had 12 coats on paint and primer on it. It was last August, I put on the last coat of color, opened the door of the shed, turned around and watched in horror as my paint turned cloudy. Too humid. Had A/C in the shed but it took only seconds for the moist air to ruin it. Wet sanding and more paint. This will be a summer project getting the dent out and repaint. I just threw color on the one I'm using now.
Steve

I forgot to say, without thinking, I cleaned my tank with Windex. They say not to use on plastics. Cracks started to appear and chips started falling off. Sometimes I can be such a moron.
Steve

Pressurizing a tank or any containment vessel with compressed air equals death or injury. Please post up pics if you do try that for the next Darwin Awards in your town. Seriously DO NOT USE COMPRESSED AIR! :dry:

Try everything else. If that fails have the pros do it. There should be a hydrostatic company somewhere. Dry ice works for small dents. Let the tank sit in the sun for awhile(if you have any...sun) then hold dry ice(with gloves) on the dent.

That's right. Dry ice is another way. Safer too.
Steve

HBKwaka wrote "DO NOT USE COMPRESSED AIR!"

Agree! If you plan to try using pressure use water. Unlike air, since water won't compress to any significant degree it will not expand rapidly and cause a violent explosion if the tank ruptures. Having said that, I doubt that using pressure will push out the dent. Ed