Fuel tanks

Pilotgeek said:

Oh quit it, CroMagnum. You're wrong and you're trying to save face. You said it can't be done and you know it. That was a home-made expansion chamber. I'm sure a professional one with pressure meters and better welding could be near perfect. This was hydroformed. (Even more pics and info )

As far as perfection... how many people slap some random 50cc pocket bike pipe onto their 66cc china girl with decent results? I've seen it more than once. Yes, it's great to be precise, but these engines aren't very precise to begin with.

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Like I said, a lot of people make a lot of junk in their backyards. It doesn't mean it's always a good idea.

Pilotgeek said:

Back on topic though, I think making a tank using hydroforming is a wonderful idea. You could get some really nice smooth shapes out of it, even if it may take a few tries.

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Did you happen to read the Wiki page that locell posted? I quote - "Hydroforming is a specialized type of die forming that uses a high pressure hydraulic fluid to press room temperature working material into a die."

Hydroforming is using high pressure fluid to press metal into a mold. It's not "hook a hose to it and blow it up like a party balloon."

Ludwig II said:

Cro, I'm baffled. This technique has been around in the 2 stroke racing world for years, and is the method of choice for ultimate accuracy. Why are you having such difficulty with it?

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Well, I've been racing and modifying 2-strokes since I got my first Yamaha 90 back in 1969. (My first bike was a 1966 Honda C50, but that was a 4-stroke so it doesn't count here.) In the heyday of motorcycle publication I used to prowl bike shows and even the editorial offices and talk to the editors. I personally met and spoke at length with Gordon Jennings on several occasions before he wrote "The Two-Stroke Tuner's Handbook." Since I lived in the same neighborhood as Rick Sieman, Pete Szilagyi gave me a giant CZ sticker as a prank to put on top of the GYDBT. If you read Dirt Bike Magazine in the early 70s then you know what that means. I've been welding up my own exhausts and frames since I got my first torch back in junior high.

So I've been around the block a couple of times.

I have heard of this party balloon method before, and maybe it's more popular in the UK and with American squids on go karts. But nobody I know really takes it seriously. And here's why:

When you force metal into a die it tends to forge the metal. It actually forces the molecules in the steel together and makes it stronger. This is what Detroit does hydroforming body panels, and what Harley does to make their "museum quality" frames.

The Party Balloon method here does the exact opposite - it stretches and weakens the metal making it prone to cracking and failure. Basically creating an accident waiting to happen. Now if this happens to your exhaust and it springs a leak or breaks, no big deal. Your bike is just louder and runs poorly until you can get home to replace it. But if your gas tank fails, you could be in trouble.

Once again, blowing up some metal like a party balloon is not hydroforming. It's just cheesy backyard engineering. Good luck.

one thing i have read by using hydroforming as an art form,using a porto-power hydraulic pump.with water.just drain it and replace the oil when done.
now depending on the amount of pressure used,it can be safe to create desired shapes to be welded together to create a fuel tank.
beating something to death with a hammer doesent stretch or weaken it?
or how about welding it?
grinding doesent make thin spots?
in comparison to the supplied china girl fuel tanks,hand fabricated tanks cant be worse than that,unless you soldered soup cans together.hang on,i think that was done and better than a china tank.
if it wasnt for cheesy backyard engineering,we would all be walking and killing our food with a stick.

i was a backyard mechanic long before i was a licenced one.

Hey i still kill my food with a stick ! Lol