Using Heat and Compressed Air to Remove Dent from Gas Tank

I've heard of people doing this also but I don't know how successful it is. I've got a tank from an older 1100 Suzuki that has a dent that I had actually thought about trying the same thing on. I ended up picking one up off ebay years back.

I was more concerned with the tank distorting or rupturing at a seam than anything.

Be curious to know how it turns out though... I still have that dented tank out in the rafters.

Switchman wrote: "Speed doesn't kill. Sudden stops, brick walls, and old women in Buick's do."

The small tank was on my 600cc VLX, V-twin I had to lay the bike down at 35 mph to avoid hitting the 80 year old lady (no kiddin!) who ran the stop sign. When the cop wrote 2 tickets (for negligence and failure to stop) I thought she was going to have a heart attack!

The dent on the big tank (my 1800cc VTX, V-twin) happened while banked steeply in an exit coming off an expressway. A large dog or deer jumped in front of me. I forgot you don't use brakes when banked. The animal survived and I managed to drive home.

L.J.

There were some comments on CR4 about pressure testing a tank. I know that your pressures are much lower, but still the stored energy of compressed air is a worry to me. From your posts, I believe you are smart enough to think your self through this. The safest way I know of to pressurize something is your hand pumped grease gun.

If the cap is on, and you fill it up with water, then adapt your fuel outlet to 1/8" pipe thread. You can then fit a grease fitting to that. Just pump the grease gun till the pressure in the tank causes the dent to be forced out. If the fuel filler cap starts to leak, you may be able to use a rubber freeze out plug as a substitute. It might require some tapping with a plastic hammer to help coax the dent out. With luck it will not need painting. The volume of grease should only be equal to the volume of the dent. Should be a cheap SAFE way to repair it. Good luck.

Hi Bob!

Thank you for nice comment.

I propose to first try a hand held torch running MAPP gas initially, not my acetylene rig, simply to keep the temps down. I only want to heat the metal to where the pressure forces it out.

Then idea of using water was only to inhibit the combustion of any residual volatiles. Probably not needed but it appears the prudent thing to do. Besides which the extra weight, about 14 pounds on the smaller tank, will help stabilize the tank.

The drawback to the water is that it will most assured draw off heat, thus requiring more heat than if dry inside. I'd hoped to keep this procedure simple and not have to manifold a pressure gauge into the preparations. However, if there is risk of elevated pressures from steam, I may have to.

The main concern was preventing a violent rupture of the tank.

About 30 years ago I knew a man who ran a radiator repair shop and who worked at repairing auto gas tanks. One day the shop closed and he was no where to be seen.

Someone volunteered that he'd been seriously injured when gas fumes in the tank blew up while he was welding on a new filler neck.

That tank had been fully immersed in some kind of leaching fluid for two days, prior to the attempt, a process he had used successfully for many years without incident.

Although I never saw him again, those who did say he looked like he'd fallen into a huge sewing machine.

It's my memory of that man and that explosion that prompts this request for comentary from others.

We'll see.

Thanks

L.J.

There is a company in So.Fla that is called Dent Magician. They seem to be franchised, so they could be anywhere. They are specialists at removing dents from sheet metal without damaging the paint, or surrounding metal. You might find one near you that could help.

Just how well do you like being on the top side of the grass? Insurance paid up? Will made out? Pressurizing a non-pressure rated container of any type is dangerous, and besides, if the dent has a crease,forgetaboutit.I suggest a dent puller to remove most of the dent, then fill in with solder. That's right,lead plumbing solder. Bondo will not hold under gasoline very long. A very high wattage tinsmith soldering iron is recommended: no flame.The torch- heated type of tinsmith soldering iron will also work.I have done it with butane, but I do not recommend it to the novice. If soldering,flush tank with detergent and water thoroughly first,and fill all but the small area around your dented work area with water.This will keep the remainder of the tank cool.Clean the area down to bare metal,using coarse grit sandpaper.The little scratches create a lot of bonding surface area, and use RUBY FLUID,or other tin flux to clean and prime the area.Apply a thin tinning coat of solder first,to make sure you have a good bond with the surface.If it does not adhere to any spot,clean and flux again.Once you have a clean,shiny,silver surface of solder,then go back and build up above surrounding surface.Any solder that looks like a round or half round drop of water standing on the surface is not bonded.More heat is required.Careful application of heat is required to build up without melting previous layers and dripping into tank from dent-puller holes. After this, sand,prime, and paint.Properly done, no leaks, and invisible. Be careful. Know safety,no pain. No safety,know pain. As a card shark once told me:If you can't afford to lose,don't gamble. HTRN

Laughing Jaguar. You may need to change your name if you attempt this method of dent removel. This amount of pressure far exceeds anything this vessel is designed to handle. A vessel of this volume under this much pressure is capable of launching the cap at a velocity great enough to kill. There is no need to exspose yourself or others to something this powerfull and unstabile. Use the safe method of filling the tank with an inert gas and drilling holes in the under side of the tank and use a rod to access and push out the dent. The end of the rod can be bent over or shaped to correspond to the surface of the tank. Afterwards fill with an inert gas and weld up the holes. Another method would be filling the tank with an inert gas and use a dent puller that utilizes a stud welded in the middle of the dent for a puller to be attached. Put safety above all else. J.Conway

You need to determine a couple of things. First is real cost to replace your tank. A new tank from the Honda dealer is going to be very expensive, like you said. But there are a lot of bike breakers out there and of course ebay. I did a quick search and found a few ranging from 150bucks upwards of 750 for a new one.

http://motors.shop.ebay.com/items/Parts-Accessories_Motorcycle-Parts-Accessories__W0QQ_nkwZvtxQ201800Q20gasQ20tankQQ_fromfsbZQQ_trksidZm270Q2el1313QQMake247a0eZHonda42abae4

You also need to determine whether or not it is feasible for you to get a good clean home repair / paint that you can be proud of. If the damaged area is really pinched or creased then the method you're thinking about is not going to help. The dent will need to be pulled and edges knocked in then bondo applied. If you really enjoy and are very skilled with body repair then go for it. But I have seen many examples where attempted repairs really should have gone out for repair. I have also seen people spend 50hours doing a repair and then do a $20 rattle can paint job.

I don't know your location but if in the US take a look at EmpireGP... I know a couple of people that have had repairs done by them. http://www.empiregp.com/ . And there are many more shops like this.

That Link to Empire GP is appreciated.

I'll take some pics of both tank damages and send them for a quote.

Thanks Switchman!

L.J.

If you decide to try the pressurized dent removal, provide a method of pressure relief such as a regulator valve. The temperatures required for the metal to become maliable will most likely cause the pressure in the tank rise fairly quick.

Another option may be to check out 'paint-less dent removal' in your local phone book. I used to work at a car dealership, and we had a company with a mobile unit (i.e. a pickup truck with tools in the back) come in to do all our work on site. You'd be surprised at the tight spaces they can get in and out of without damaging any other parts. Another bonus, I never saw a bill for more than about $50 from anything that they could do. As mentioned before, so long as the dent is not creased you're likely that it will come out totally, and probably will not damage paint.

Note also that if you can't find a specialist in paint-less dent removal, swing by your local car dealership and ask them who does their body work. Most places don't do it in house, but they have someone they recommend.

Best of luck!

-MechMatt

Hi MechMatt!

I don' have to go that far to find such talent: the guy in the hanger next to me owns such a business.

In this weather, I doubt he'll be doing much flying but I'll tack a note on his door anyway.

Thanks for the suggestion. I'd completely overlooked this.

L.J.

I had dented racing car exhaust pipes repaired in exactly this way, (without using water) by a braver man than I. Let me suggest that you pressurize the tank with a non-oxygen gas like CO2 that will not effect combustion of any residual hydrocarbons.

Good luck!

RC

If you will completely fill your tank with water or oil and pressurize in a controlled way it will more than likely push the dent out of your tank unless there is a sharp bend in it. If there is a kink in it, tap the bend with a hammer and work it out. With the hydraulic pressure inside it will act like an anvil that you can hammer against since it is non-compressive.

Air is real dangerous because it's so compressive but using the hydraulic method is much safer in that it isn't so explosive if it should rip your tank apart. A hand pump is the best way to do it because of the control you have and should the tank come apart there is only a small squirt of oil and normally not enough to cause any damage.

You are proposing a hydroforming method when you pump water into the sealed tank. This usually forces the material against a mold. Simply pressurizing the tank may pop the dent, or it may find a weaker area - like a seam - that will give away first. A dent, especially an inverted dome shape, can be quite strong. I would suggest some support for the tank walls. I'm sure that an actual mold would not be economical here, but burying the tank in sand, with a void created for the dent area to expand into would increase your chances of success. If the tank did rupture in the process, it would be less dangerous under sand than in free air.

Fuel residue can be a problem for a long time. you could vaporize a tarry residue and produce flammable gas.

The problem with dents is that you have usually stretched the material and now it has to go somewhere but that somewhere usually won't fit in the original shape.

I am going to explore an alternative.

Instead of the risk associated with heat, pressure, etc., I may simply remove the paint from the damaged area, fill in the dents and, after sanding and priming it, coat both tanks with mold release.

Then pull a fiberglass plug from each tank to use as a mold for fiberglass replicas.

I've been making composite parts both with and without autoclaves, bagged and not, for almost 30 years.

Why not?

Thanks for all the comments and supports

Have a great holiday.

L.J.

I am entertaining filling the tank with water partially,

Please explain, are you going to fill the tank or only partially fill the tank? . I would assume the latter.

The LEL for petrol is 1,4% and the UEL is 5,9%........the tank could still be a problem on heating with compressed air, the rough surface of the tank could still hold minute amounts of petrol and vapours could be liberated on heating. May I suggest that you partially fill the tank with water and pressurise with an inert gas, e.g. Nitrogen. Always better to be safe than sorry.

Although this is a much larger tank, the same problems can exist.

This method of removing the dent may well work if there are no sharp edges on any on the dents.

Do NOT forget the inert gas!!!!

I am have a tank with the same problem. Been thinking about using air pressure and propane with oxygen instead of actelene. Propane heats slower and more controlable.

I am not recommending this, but if I were to try to remove a dent here's how I'd do it.

Bury the tank in sand, with the dent on top and uncovered. Fit a hose to the cap with a quick-release valve. Fill the tank with water, drop in some dry ice, and cap it. Move to a safe distance (preferably behind a shield) and watch for the dent to pop out, then open the quick-release.

DO NOT DO IT!

When I began reading that you pressurized the tank to 35 psi with air I was a little concerned. But when you suggested going up to 100 psi I became VERY concerned. It is more dangerous than you think. I've worked with pressure testing many times and I have seen some nasty results. Even as low as 5 psi in large volume vessels.

Completely filling the tank with fluid and purging any air from your pressure system is an option. But your heating idea will probably not work with that volume of fluid cooling the metal. And you will (as mentioned) probably pop a seam before the dent comes out.

Also..... I've repaired a few motorcycle tanks. I worked with a guy that did tins for Harleys and other bikes. The metal of these tanks is typically very thin. Thinner than typical body metal. Applying heat to the thin metal would be difficult without popping it or deforming it out too much. Once it gets hot enough to move what's to stop it?

Even using the proper tools to repair a tank it is a little difficult to not create a hole in the tank. The last tank I did I used a stud welder. It fastens a puller stud to the dent like a spot welder. And even with this tool you have to be very careful to not burn through or pull out the thin metal.

I would try one of those suction type pullers first. It should work well on the thin metal. Get it as close as you can and then glaze over the area to blend it in. You will probably find that blending it so it looks good will be a bigger job than pulling the dent.

....just my 2 cents

7to 11 lbs of pressure is what I will try, if I ever get around to it. Just to see if it would work. The old tanks will have good quality steel unlike the brittle new tanks.

Tanker trucks are repaired al the time by pressurizing the tank with water. The tech told me there is no danger of a tank explosion at all. the logic behind this is hydraulic action. However, you MUST BE SURE that there are NO AIR BUBBLES in any of the pieces of the system. Eg. the tank, hose and pump. Good luck and be Safe.

maybe you might want to consider not putting pressure on the tank or heating it with a torch. as much as i would not use a damaged tank when my crotch will be over top of it that may not be of concern to you, but then again thats your choice.that related you might want to consider using the same type of epoxy patch material that is used to repair pin hole leaks in car ant truck gas tanks, this requires the work to be done by a very experienced and heavily insured company, it

repair or resealing a motorcycle gas tank is NOT something to do in the backyard.

'da ber

Is it much of a dent? I've used a tool called Ding King on the car to pull out shallow dents but it won't work on one with a real crease round it. You can buy it in lots of places.

There is a metal shrinking trick used by auto body guys back in the day where they heat a very small area to cherry red with a torch and cool it rapidly with a sopping wet rag. However the thickness of steel used in body panels is probably thinner than that used in an M/C gas tank. So it may not work so well in your situation. It is also somewhat of an art and you can have a bigger mess than with which you started.

I wouldn't pressurize the tank as you suggest. My guess is that you would have to get the dent cherry red or close to it before the steel would deform from the pressure against it. Heating a small area to that point you're more likely to just have it blow a hole. Flying hot shards of metal does not sound fun.

I've seen this demonstrated on a car body dent but using an aerosol hair spray can for cooling. Much less heat was used & it did not damage the paintwork but, obviously, the steel is pretty thin on a car body.

an aerosol har spray can? sounds interesting, how was that trick done, by whom?

'da ber

My dad used to use dry ice applied to the center of hailstone dents after the vehicle had sat in the hot Texas summer sun to pop them out, I presume the freeze spray used to troubleshoot thermal problems with PC boards could work similarly.

This video shows how it works, different aerosol to the one I remember but same technique. I think it relies on gently expanding the whole area then cooling just the dent which pops out as it shrinks.

If your dent is not creased, you can try the suction cup method. Don't try it with a toy. Use a real suction cup designed for this use. To increase the effectiveness, fit the tank to something stationary, and use oil, or grease to increase the holding power of the suction cup. The comments I am reading are implying a thin metal tank. The heating might cause the metal to expand, making it harder to pop back out.

If the suction cup method noted above does not work, there is a more aggressive bit of kit you might look into. There are stud welders that body men use to temporarily weld a 2 or 3mm stud to the panel and then they use a sliding hammer to pull the dent. Then they use an angle grinder to grind the stud off. I know harbor freight carries them, other places may as well. I've also heard of devices that use a special high strength hot melt glue to glue studs to the panel that will release when re-heated, although I've never seen one.

Laughing Jaquar: pay attention to this response, cause there may be a test, and if you get it wrong and use open flame you just may fail the test, loose your hearing and possibly your eye site.

I have tested under ground water mains that I supervised the construction thereof. Because we fear explosion as the result of high pressure, we totally fill the water main with water. We place bleeders where they are needed to relieve any possibility of trapped air. We often test a mile or more of this kind of system at one time. The pipe diameter may be any where from 12" to 24 " and is constructed generally of c-900 poly pipe. The blue stuff!

After filling the pipe and bleeding off any possible trapped air we use a stand pipe with a fitting on it that will permit us to pressurize the system with 150 psi of atmosphere.

If the system leaks down more than 2 lbs of pressure in 24 hrs, we must find the leak and repair it. The reason that we saturate the system before applying the pressure is just plain common sense. If we get a catastropic failure it will not amount to anything more than a PSSST and the little bit of air is no longer meaningful, and we don't blow up anything.

Therefore with your caved in tank I suggest that you invert the tank and where the fuel pet cock is, install a fitting that will permit you to apply a fixed amount of air pressure and increase it gently by adjusting the pressure controller on your air compressor. Then turn the tank upright and fill it with water and put the unvented cap on it. Turn it back over, place it into an empty trash can and slowly apply the air pressure. One of three things will happen. Likely the dent will pop out, or the cap will leak, or a seam will fail., but you are not likely to be harmed!

If the dent is in an area that you could get a small plumbers expansion blatter into you might try just using that and your compressor to accomplish the same thing , but somehow I don't think you are that lucky.

TMF

apparently you havbe seen first hand what happens to a pressure cooker when it is not allowed to vent properly. from what i read sent the enquire's original and subsequent posts it seems to me he is either looking for ways to come up with a commerically viable way of repairing motorcycle fuel tanks something along the lines of the old gas tank king franchise, or he/she does not intend to think about what can be done to come up with ways to solve his /her problems or more likely has a death wish he /she wants someone to bear the bear the problems attached to the granting of.

'da ber

The traditional method of dent removal in a steel petrol tank- purge vapours, fill with inert gas or water, invert so bottom upright, use air chisel to open enough to gain access to dent- use hammer & dolly to get as perfect as possible- weld up opening using oxy-acet or mig- test for weld soundness with comp air & water(or petrol)- use body filler to get surface perfect prior to rubbing down/painting.

I would try filling the tanks with water, then stick 'em in the freezer. The ice will expand and there's a good chance you will get a satisfactory result, depending on the dents and their position on the tank. Keep a close eye on 'em though, as you run the risk of splitting seams...

Cheers

After all of this input I can't wait to hear how it works out.........

gdevine wrote: "After all of this input I can't wait to hear how it works out........."

After all of this input I may take up gardening!

L.J.

Ah but if you aren't careful you might be pushing up daisies from the wrong side of the dirt....

I did exactly this on a DR400 tank may years ago, when I applied the compressed air the tank tried to flatten out from it's saddle shape and when I pulled it back together I got a crack in the aluminium. I ran a car exhaust through the tank for a while and gave it to a welder who fixed it.

The exhaust fumes did the trick cleaning and scavenging but I wonder if catalytic converters would make any difference to the effect?

The exhaust fumes did the trick cleaning and scavenging but I wonder if catalytic converters would make any difference to the effect?

Not a problem, in fact better, all the catalytic converter does is reduce the toxicity of motor vehicle emissions..........especially carbon monoxide.......and to meet EPA requirements, including prevention of emissions of unburnt fuel. The gasses are inert and will not support combustion.

NOTE:- By using exhaust gases without a catalytic converter there would be a risk of explosion. i.e. Carbon monoxide and unburnt fuel are both highly flammable.

freeze it

<...entertaining filling the tank with water partially, tilting the tank so the dented area is the highest part of the tank, applying compressed and pressurize the tank with 100 to 125 psi...>

Please ensure that no other CR4 reader is in the immediate area before commencing this operation. Please also check that insurance cover is in place to look after the eventualities.

It would be safer to apply a high-quality body repair filler to the outside of the dent, then smooth back and repaint, particularly as <...slowly heating the dented area with a torch...> from the original entertainment will require a measure of repainting in any case.

10 years later.. nice