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Discussion Starter #1
Hi. I have a CB200 tank to go on my XBR500 build and need to get clearance where my frame rails attach to my top tube. At this location, the tank tunnel is 130mm and if possible needs to become 160mm. Having googled around, I hope to be able to use a plastic mallet. Any advice on weight/shape of mallet and technique - do I strike against the inside face of the tunnel first, or the bottom edge where the wall and bottom of the tank meet? Any prep to help move the metal most effectively? I thought about filling with boiling water, but I could always purge the tank of petrol/gas fumes and use a butane torch. Many thanks.
 

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That tank is 2.9 gallons, down from the 5.2 gallons on the XBR500. Are you prepared to wind up with a 1.5 gallon fuel tank?

don't purge fumes with fire... if you must do something, rinse it out several times with water first
 

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Good luck with that - I tried to dent the tunnel on a GS650 tank to fit over the head of a 450 and only had to move part of the tunnel less than 1/2 inch each side in just a small area and the outer skin still deformed.

You'd probably be best off cutting it out and re-welding.

But I doubt you are set up to do this seeing you are asking here.
 

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If you're referring to the the black circled marks in the pic, all you need is the round side of a ball peen hammer. I assume by plastic mallet you mean a teardrop. A teardrop won't work as well here. I work mostly with a repoussé and a ball peen for work like that.
 

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Discussion Starter #6
If you're referring to the the black circled marks in the pic, all you need is the round side of a ball peen hammer. I assume by plastic mallet you mean a teardrop. A teardrop won't work as well here. I work mostly with a repoussé and a ball peen for work like that.
You're right, it is the areas circled. I suppose I need to reverse the corner. No problems with losing capacity, I can't ride far.
I was thinking to use some oxalic acid I have handy to derust and purge the tank. Any chance you could link me to the hammer you would use for this job, as I don't know what face size, weight is best? Will it need heat? Many thanks.
 

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Rust is the process of iron in the steel turning into soil. Your tank was originally cold formed supposedly using new steel, now it's old rusty steel so it is thinner in places then it was originally, if you just try to hammer it into a different shape I would expect a better then 50% chance you will end up with a leaker. :I think you need a new plan.
 

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Discussion Starter #9
Rust is the process of iron in the steel turning into soil. Your tank was originally cold formed supposedly using new steel, now it's old rusty steel so it is thinner in places then it was originally, if you just try to hammer it into a different shape I would expect a better then 50% chance you will end up with a leaker. :I think you need a new plan.
I got it for a song, so if it fails and I can't get it brazed, it's no big loss and I might learn a bit along the way.
 

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why on earth would you trade that great looking xbr500 tank for a useless cb200 tank?

Old honda tanks are thicker metal than later tanks. They are also crimped seams. For the most part working slowly and tapping more than tapping harder is the way to go, the last thing you want is the metal to pull because you are hitting it and then the seam at the bottom splits.

But back to this partially uselsess and ugly mod for a second - have you ever seen a GB500?

1990-honda-gb500-tt-rr-1024x735.jpg

This uses almost the same design tank as what you have and it is proof that you can have a pretty, functional, and retro design using something as "modern" as your tank.
 

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Discussion Starter #12
Thanks for the tips on striking. Yes, beauty is in eye of the beholder. The boomerang comstars are going as well. If I can't get the CB200 tank to fit, I've got a CB350 which would need less work.
 

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Discussion Starter #16
If you're referring to the the black circled marks in the pic, all you need is the round side of a ball peen hammer. I assume by plastic mallet you mean a teardrop. A teardrop won't work as well here. I work mostly with a repoussé and a ball peen for work like that.
Your advice worked well, thank you. 30mins of fast, short strikes produced the results in the pic, along with a resolve never to engage in an arm wrestle with anyone who shapes metal this way on a regular basis!
 

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Discussion Starter #17 (Edited)
I went to the local shop where the petcock bung was TIG welded into it's new position. The guy says the tank is old and thin and has to switch to MIG to build up a weld over the two original petcock holes. On testing, the weld is leaking at it's base.
My question is whether a tank sealant like POR15 will sort this out, or has the metal on this this tank become too porous and so beyond help? Thanks.
 

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POR15 should solve the issue.

just make sure you follow the directions to the letter
 

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Find a competent welder. I can build plenty of metal up with tig. In fact, it's the preferred method for thin stuff.
 

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MIG is fine if you learn how to work with it. I have no TIG, so I do all of my welding with MIG and O/A. In sheet metal, burn out comes from penetration. In welding thinner gauge sheet metal, you want to lower your feed speed and lengthen your stick-out. Longer stick-out = less penetration. Lower feed speed = less amperage. The other thing is voltage. Lower volts = narrower puddle. Higher volts = wider puddle.
 
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