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metalhead777

cutting and rewelding a gas tank?

19 posts in this topic

Im wanting to cut 3-5 inches out of the center of my cb750 gas tank to shorten its length and then weld it back up. Problem is its been used before, and I know for sure that its had gas evaporate into it. Someone told me that cutting and welding a used gas tank like so is about as dangerous as trying to wrestle a hungry grizzly-bear while wearing a suit made out of raw meat and honey (Im paraphrasing of course.) I've seen some guys on this site cut and weld old tanks though. I am a welder by trade, and I've always been told not to weld on fuel tanks. Im coming to you all for opinions and tips on this one.

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Either have it boiled out at a radiator shop or steam clean it.

Dusty

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I've welded a bunch of tanks(car & bike), I hook a hose to a car's tailpipe & run exhaust thru it for about half an hour. It drys it out somehow. If I'm nervous about it I'll weld it while connected to the car. If you're gonna cut your tank apart anyway, scrub the inside real good, JB weld works real good to plug pinhole leaks, but bondo may not stick too good. I haven't blown up yet!

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Hot water and non petroleum based de-greaser works pretty well too. If you're still worried fill the tank with Stargon from your MIG or Argon from a TIG tank, the inert gas will keep the tank from exploding.

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I welded on one tank that I was sure had been used. I wash the inside of that with plenty of degreasing soap repeatedly (think Dawn. if it cleans baby ducks at oil spills then it should work on my tank). Then I carefully put a match in just to see. When no reaction happened I proceeded to cut and weld as needed. My tank had a bit of rust in it. Thinner metal from rust made for lots of blow outs to repair. Once I got it all together I looked for leaks with water.

The prep that Dusty mentions is probably way safer.

If you are feeling... .... ...adventurous, I have heard of people denying the spark oxygen by filling the tank with an inert gas; say maybe a second line from the Argon tank. But there are some folks that will turn on the car and run a line from the exhaust to gas tank. That seems like it would be hard to control if you are cutting the tank in half. There's aught to be lot of oxygen that could find it's way in when it's cut in half. When I started writing this Joe and Slime hadn't replied yet. It took me that long to find the below links.

this is one time I did some welding on a tank.

http://www.thechopperunderground.com/forum/index.php?showtopic=69996&hl=%2Bgas+%2Btank

Here is another tank I modded a little.

https://www.facebook.com/ward.swann/media_set?set=a.758928734120650.1073741827.100000105919292&type=3

Edited by Pluto

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Pretty much what I plan on doing is using a cut off wheel to chop the tank, remove several inches, then reweld it back. And now, using my advanced computer editing software (Aka Microsoft paint) I will now show you what I am attempting to do!

post-36697-0-10745400-1430971652_thumb.j

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Pretty much what I plan on doing is using a cut off wheel to chop the tank, remove several inches, then reweld it back. And now, using my advanced computer editing software (Aka Microsoft paint) I will now show you what I am attempting to do!

Hey, your bike shrunk too!

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It can be done but you need to be very careful.
the thing you need to remember is the fire need o2
Take it out and replace with non flammable gas like argon and you are safe. It will be expensive but well worth the keeping of ones hands.

Carbon monoxide can be used but be aware that a rich running engine can still put out unburned gasoline. Add the possibility of o2 sneaking into open spaces that are not welded and you have a possibility of ignition.

If you are not 100% comfortable with it have someone do it with experience.

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Fill it with water and start cutting.

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Gas vapor is what burns. If you get out the liquid fuel and let that sit open a few days to evaporate. Then wash and dry. I haven't had a problem.

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Pretty much what I plan on doing is using a cut off wheel to chop the tank, remove several inches, then reweld it back. And now, using my advanced computer editing software (Aka Microsoft paint) I will now show you what I am attempting to do!

Hey, your bike shrunk too!

I know it. Damned techno-lology trying to shrink up my wheel base an demolish my engine

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Co2 fire extinguisher give it a good squirt and go for it

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I've welded a bunch of tanks(car & bike), I hook a hose to a car's tailpipe & run exhaust thru it for about half an hour. It drys it out somehow. If I'm nervous about it I'll weld it while connected to the car. If you're gonna cut your tank apart anyway, scrub the inside real good, JB weld works real good to plug pinhole leaks, but bondo may not stick too good. I haven't blown up yet!

Carbon monoxide poisoning splains alot!

Dusty

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Pretty much what I plan on doing is using a cut off wheel to chop the tank, remove several inches, then reweld it back. And now, using my advanced computer editing software (Aka Microsoft paint) I will now show you what I am attempting to do!

hay that'll be sharp!

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Gas vapor is what burns. If you get out the liquid fuel and let that sit open a few days to evaporate. Then wash and dry. I haven't had a problem.

yah I think the vapor is heavier than air too, I'd let it sit upside down.

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hmmm.. wish I would have known this stuff, I drained all the gas, let sit for a week then I lit my tank on fire bout a one foot flame came out the spout but it was all burnt out and clear to cut. atleast I know for next time!

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I dont do anything and im fine.

Big-Romotion-Horrific-Rotten-Burned-Band

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I just cut the tank open on my running bike today. I simply dumped the gas out, washed it out with dish soap, rinsed, then cut it open. No big deal.

I've done it this way several times but I wasn't sure how fresh the gas was in the previous tanks.

Edited by Dieselchanic

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