HBergh Posted September 25, 2011 Share Posted September 25, 2011 I would like to know if anyone else with a DA has had excessive vacuum occur in the gas tank such that the gas tank metal started to collapse. Here is how it happened to me: I knew my gas tank was pretty empty while in my shop but I had started my DA several times for static test engine runs. When I decided to go for a test drive, the car appeared to stop because of not enough gas in the vacuum tank. So, I added about a half cup of gas into the vacuum tank. The car started and ran for a couple of minutes and then I heard the sound of thumping metal. When I tried to removed my gas cap it was nearly impossible because of the excessive vacuum in the tank and I observed that the tank was dented in. I decided that with gas tank gas level was below the outlet such no gas could be brought to the vacuum tank, so it just kept sucking until the tank started to collapse. My question is: Should the vent hole in the gas cap been able to withstand this vacuum without collapsing the tank? Thanks. Link to comment Share on other sites More sharing options...
idrjoe_sandiego Posted September 25, 2011 Share Posted September 25, 2011 Wow! Hbergh- interesting problem there. My guess is you do not have a "functional" vent in your gas cap if it was difficult to remove (presuming, of course, that the difficulty was, in fact, due to excessive vacuum). The entire fuel system will fail to operate properly without a functional gas cap vent. I seriously doubt that your engine is drawing enough vacuum to collapse the tank, unless the tank was extremely weak to begin with. Joe Link to comment Share on other sites More sharing options...
Guest 1930 Posted September 25, 2011 Share Posted September 25, 2011 Do either of you have an original gas cap? Do you know how the original gas cap is vented assuming you have one ? Link to comment Share on other sites More sharing options...
HBergh Posted September 25, 2011 Author Share Posted September 25, 2011 I really don't know if my gas tank cap is original. However, when I blow on the small hole in the cap, air does pass. As long as there is plenty of gas in the tank, the engine seems to run normally. If someone has an original cap that could provide a close up image of the vent hole, it could be helpful. My tank looks solid, so yes, it was a surprise that such a vacuum could be developed in the tank. Link to comment Share on other sites More sharing options...
Guest cben09 Posted September 25, 2011 Share Posted September 25, 2011 Vent hole plugged,,,Poke it out with wire,,,Ben Link to comment Share on other sites More sharing options...
Guest 1930 Posted September 25, 2011 Share Posted September 25, 2011 I have an original cap but I am not sure how it is vented, I was hoping someone could explain it to me. Solid top no hole Link to comment Share on other sites More sharing options...
HBergh Posted October 1, 2011 Author Share Posted October 1, 2011 Now that I think I've created a well vented gas cap, I would like some ideas on how to return my gas tank to its original shape. I hope you can get an idea of what the tank looks like from my pictures.1. Could I some how safely pressurize the tank sufficiently to pop the tank back into shape?2. Should I need to take my car to a body & fender shop to have them pull out the tank from the exterior?3. Any other idea(s)?Thanks, Howard. Link to comment Share on other sites More sharing options...
keiser31 Posted October 1, 2011 Share Posted October 1, 2011 (edited) I have heard of using water as a pressure "spreader". Fill it 3/4 up with water and shoot some air into it. It is supposed to disperse the pressure and pop the dent out. I have never tried it, but have heard about this process more than once. I may try this on my 1931 DB tank. When I was 15 years old, I was under it, draining the tank when a spider dropped down onto my face. My head made a pretty bid dent in the tank when I hit it on the way out from under the car. It even knocked the baffle inside the tank loose. Edited October 1, 2011 by keiser31 (see edit history) Link to comment Share on other sites More sharing options...
Guest 1930 Posted October 1, 2011 Share Posted October 1, 2011 (edited) The creases will not go away completely unless you were to work the metal and then fill a little but pressurizing the tank with air would make a good start. Make a fitting on the hole you choose to put air into, the smallest hole may be best. Weld an air fitting onto that fitting and in between that some sort of valve with a blow by to let off excessive pressure, fill the tank up until it begins to pop, take a small dowel maybe 1/2 or so and tap on all the high spots, work your way slow starting at one end and tap gently back and forth along that crease, You will start seeing the crease becoming less noticable and you will notice the metal moving back to where it was originally. All metal has a memory, it wants to go back from whence it came, it will take time but you might enjoy it. Good luckBy the way, start at the worst crease first, you always want to try and reverse the damage in the order it took place. Dont move onto a different area until you have the majority of that first worst crease, you can also work out the dent possibly from the inside out using long whatevers but if it comes to that than you might as well forget about it looking too pretty unless you really have a knack for that sort of thing. Edited October 1, 2011 by 1930 (see edit history) Link to comment Share on other sites More sharing options...
hchris Posted October 2, 2011 Share Posted October 2, 2011 You know I might be missing something here, but I wonder why you want to go to the trouble of removing the dent. If you are worried about losing fuel capacity, you might be talking about a 1/2 gallon (2-3 litres) perhaps; if you are concerned with the aesthetics then maybe use a dent puller. The last thing I would do is pressurise the tank, as you are just as likely to weaken the solder around the tank ends, or fittings, and finish up with a leak. Link to comment Share on other sites More sharing options...
knobless Posted October 2, 2011 Share Posted October 2, 2011 I just removed a original tank off my 34 DR it too had a dent almost exact location,but the dent was my last concern, someone had sealed the tank with what, I have no idea but I do know whatever material they used was now pulling free from the interior of the tank walls and clogging everything, I purchased a new so called "Original tank on eBay, but be careful if you go this route filler neck does not fit waiting on 60 degree hose, to work?, also all locations for hook ups are in different location from original, as for pressurizing the tank, I dont think I would try it weak seams could spell new tank........JMHO..... Link to comment Share on other sites More sharing options...
MikeC5 Posted October 2, 2011 Share Posted October 2, 2011 The highest vacuum attainable in the tank (i.e. a perfect one) would only put a 14.7 psi pressure on the outside of the tank. So it really shouldn't take to much air pressure in the tank to pop it out. If you have a spare gas cap try drilling a hole to fit a tire valve stem and then use a compressor to put air in. I would not go above 20 psi or so or you may create leaks. Also, you will need to remove the fuel inlet from the vacuum tank and plug it or gas will be forced out there. Whatever you do be careful with the gas fumes. Link to comment Share on other sites More sharing options...
Guest cben09 Posted October 2, 2011 Share Posted October 2, 2011 A tank rupture at 20 # could be very bad,,Most of you guys have not had a tyre sidewall let go at 20#,,,I will assure you its not to be forgotten,,Fill with water and apply pressure slowly,,,under control,,,,Be careful,,Ben Link to comment Share on other sites More sharing options...
Bullfrog_eng Posted October 2, 2011 Share Posted October 2, 2011 I agree that it should not take much pressure to pop it out (with any luck!!). I would just stuck the nozzle of a air dusting gun, or some similar device, into the tank with some rag wrapped around it to seal it. Just hold it in by hand, don't modify the cap. I think you will get quite enough pressure in the tank that way and you can just release your hand and the rag will blow out if things start to look a bit ugly. Assuming there is a pressure regulator on the air compressor, set it fairly low to start off with (10 PSI??) and see what hapens.I use this method to test 4X4 fuel tanks for leaks when I build them, I put a bit of Diesel in as well and the air blows it everywhere and soon shows up a leak. Good luck,John Link to comment Share on other sites More sharing options...
keiser31 Posted October 2, 2011 Share Posted October 2, 2011 A tank rupture at 20 # could be very bad,,Most of you guys have not had a tyre sidewall let go at 20#,,,I will assure you its not to be forgotten,,Fill with water and apply pressure slowly,,,under control,,,,Be careful,,BenI agree. Link to comment Share on other sites More sharing options...
Guest 1930 Posted October 2, 2011 Share Posted October 2, 2011 I think the key thought is to use common sense, fuel tanks and radiators are tested using air every day still to this day. If you put a blow by valve on the fitting at some point than the pressure will not be so great and you will also be able to acomplish what you desire hopefully and that is repairing the tank. Link to comment Share on other sites More sharing options...
60ch Posted October 2, 2011 Share Posted October 2, 2011 If you are going to use the air method to push the the dent out you will not fill the tank with water. You want air under the dent and water everywhere else. The idea is to get the air to push the dent only. Do not weld to the gas tank. modify a gas cap with an air fitting and make sure the vent is sealed in the cap. Position the tank so that the air is under the dent and slowly apply pressure. Tap around the edges of the dent to unlock the stress. This can be a dangerous proceedure since you have no way of knowing how thin the metal is in the tank. In my experience they rust the most on the bottom where you are dented. Your tank may be very thin there already. Consider leaving it as is or taking it to a professional. :eek: Be Carefull Link to comment Share on other sites More sharing options...
dwollam Posted October 2, 2011 Share Posted October 2, 2011 I agree with bullfrog. Wrap a rag around an air nozzle and apply it through the filler neck. You don't want huge amounts of pressure. Link to comment Share on other sites More sharing options...
Guest Harold Phillips Posted October 3, 2011 Share Posted October 3, 2011 In the orig. problem I think what happened is the gas tank was empty and the vacume tank continued to suck air until the small vent hole could not keep up. by priming the vacume tank so the engine could keep going long enough this is possible,thank you for making me think about this as I will make sure i have gas in tanks as well as priming vacume tanks. Link to comment Share on other sites More sharing options...
HBergh Posted October 3, 2011 Author Share Posted October 3, 2011 Thanks, everyone for all your great suggestions and general discussion. Harold: You are exactly correct with my original condition. My goal with my delimma announcement was to find a reasonable solution as well as to alert others of this type of condition. I will proceed very carefully! Link to comment Share on other sites More sharing options...
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