How do you take dents out of a round aluminum tank?

[vpt]

I have a few water witch outboards with some dents in the tanks one tank is especially bad and will be my test tank.

I am not sure on actual thickness of the aluminum but it does have some strength, I am guessing it is 12G"ish". Today I plugged all the ports and worked my way up to 130psi air pressure in the tank. It pushed some bigger dents out some, I am worried about going any higher with air pressure. I am thinking maybe moving on to fluid and a hand pump. Is pressure the way to go with these types of tanks to "pop" the dents out? You guys have any suggestions? The biggest port is only 1" and only on one tank. If all fails I could cut a window open, do the work, weld it shut, and smooth then polish. I'd rather not though.


The torpedo type tanks:

[Bob Fisher]

Take it to a paintless dent removal guy, they have tools to reach almost anywhere and press the dents out from the inside. Bob.

[Richard P Wilson]

You were lucky. You should never use air pressure in a tank not designed to take pressure, when it fails, it will be like a bomb going off. If you must use pressure, it should be water. Tricky with a polished aluminium tank, but one way with small dents is to drill and put in a self tapping screw, then gently pull the screw with a pair of pliers, till the dent comes out. Does leave you with problem of sealiing the hole though.

richard

[vpt]

I know the dangers of compressed air and the reason I don't want to go any higher with it. I put pressure in the tank while it was covered with a bog bed threw a lengthy hose. The worst that would have happened with these small tanks is a little pop and a rip in one of the tanks.

A paintless guy will cost money, more than the motor and tank is worth. Plus I like doing things myself.

I did think of screws and welding the holes shut but honestly at that point I would rather just cut it open and weld a seem. I would like to avoid welding on the tanks if possible But it might be the only viable option.

I appreciate the input though! Keep the ideas coming!

[Dr Stan]

Does leave you with problem of sealiing the hole though.

Guess one could weld it up, NOT!

[saltmine]

Screwy idea....Why not fill the tank with water, and freeze it? Of course, you'd have to watch it very closely in the event the water pushes too hard on the aluminum shell.

[lakeside53]

Pump it up with water or... hydraulic oil with a hand pump.

[davidwdyer]

I think you could use a curved steel bar with a nylon ball on the end. These are used here in Brazil to

take dents out of cars in hard to reach places. You have to be creative, but you can design your own curve and figure out how to gently

press the dents out.

Also, people who take dents out of brass musical instruments would have some tools and ideas.

[pcrc11]

I pull dents in steel at work with draw pins. There is a special gun that spot welds on a pin. Special slide hammer grabs the pin and you slide hammer the dent out, grind off the pin and go from there. Does not leave a hole. Not sure if they have a set up that will do aluminum. However you could tig weld on the same type of pin and use that to pull on, then grind and file it off and polish. Would be a ton of work but you would not have to deal with putting any holes in the tank like you would with self tapping screws. Also have to take special care that tank has no fuel residue or fumes in it when welding on it, but I did not have to tell you that!!

[vpt]

Screwy idea....Why not fill the tank with water, and freeze it? Of course, you'd have to watch it very closely in the event the water pushes too hard on the aluminum shell.

I had that idea as well. Would it work? I know the ice would push on the tank but would it push out on the dents before trying to rupture the tank? Does ice put equal pressure all around on the inside of a tank?

Pump it up with water or... hydraulic oil with a hand pump.

That is an option I am willing to try.

I think you could use a curved steel bar with a nylon ball on the end. These are used here in Brazil to

take dents out of cars in hard to reach places. You have to be creative, but you can design your own curve and figure out how to gently

press the dents out.

Also, people who take dents out of brass musical instruments would have some tools and ideas.

One other problem with a rod threw the one hole in the one tank is the hole is threaded for the cap. I'd hate to bugger up the threads.

I pull dents in steel at work with draw pins. There is a special gun that spot welds on a pin. Special slide hammer grabs the pin and you slide hammer the dent out, grind off the pin and go from there. Does not leave a hole. Not sure if they have a set up that will do aluminum. However you could tig weld on the same type of pin and use that to pull on, then grind and file it off and polish. Would be a ton of work but you would not have to deal with putting any holes in the tank like you would with self tapping screws. Also have to take special care that tank has no fuel residue or fumes in it when welding on it, but I did not have to tell you that!!

These tanks have been sitting dry for years and have no seams. I would still take precautions before welding and make sure it is safe.

The pins are also an option and I can weld aluminum pins on with the tig. But Like you mentioned it is allot of work and it would take allot of pins to get all the dings out. Once again I think I would rather cut the tanks open to do the work and weld and smooth one seam instead of a bunch of spots.

[A.K. Boomer]

fill it full of water, now add your compressed air, take it up to where you had results before, now for the smaller dents take a small weight little fiber hammer - hit around the parameters of the dents and watch them get smaller,,,

it's far safer than a tank filled with air because the water is non-compressible therefor does not add any compression momentum if the tank should blow - then the little air pocket quickly loses it's umph and instead of the thing taking your head off it basically farts and then starts to leak water at the small controlled fracture...

and unlike just using fluid the air will add enough of a springboard so you won't have to keep checking the pressure and adjusting as the dent's start to come out - it's a beautiful thing.

[jnissen]

Paint-less dent repair guys and the tools they use can do wonders. The entire industry revolves around fixing dents in metal from door dings to hail. I was a believer after having the wife's car get the hell beat of it with 1" hail. I honestly could not find where the dents were. I must caution you that not all dent guys are the same. The guy I used has been doing it for 20 years and is very good. I wouldn't even attempt to do that with water or oil in a pressurized manner. Your more likely to blow out a seam or warp the whole tank. I've tried to repair dented aluminum tuned pipe for two strokes and they are small and hard to get to. Tried freezing water with only very minor success and pressurized one as well and it only ballooned the pipe and did not really get the dent. I've had the best luck with a smooth ball on a long slender handle and just work it out over hours and hours of tapping on the inside to work out the smaller dents. Large dents I just toss the pipe in the trash as I've not found a good way to really save them.

[Toolguy]

How about holding dry ice against the dent with a rag? It makes that one spot shrink and become stretched by the surrounding metal, thereby raising the dent. I have not done this myself, only heard it talked about and there may be some technique involved in getting the best results. A paintless dent removal guy told me it was one of his tricks but did not discuss the details.
You might see what you can dredge up by Googling Paintless Dent Removal.

[Evan]

Place some dry ice on the dents and hold it there for a couple of minutes. That will cause the aluminum to contract significantly and may cause some of the dents to pull back out. This has been used to repair hail dents with success. It may work even better if the entire tank is first heated to boiling water temp by pouring hot water over it.

Beat me to it. I was typing...

[JoeCB]

The early outboard motor shop manuals tell the "how to" ... add air pressure, but only 20 - 30 psi. Then using a small torch heat the dent and begin tapping around the edges. The heat will reduce the strength of the AL allowing the air pressure to push the dent out. Now, please understand that this will not work on a deep "creased" dent. And be darn sure that the tank is purged of all gas vapors. Your Waterwitch tanks are cylindrical in shape, most outboard tanks have flat sides, if you try pumping these to 130 psi you will either end up with a "basketball" shape or the tank will burst. And yes, I'm quite sure that your Waterwitch tanks have a brazed seams.
Joe B