[Candyman]

So lets hear some thoughts about modifying tanks.

Two options obviously are fiberglass or welding. Fiberglassing might have issues bonding well with the metal (I've never tried to join the 2), but welding would be a bit of a hassle for those who don't have much of a shop.

Are most tanks steel or stainless? I know older tanks were steel, but did they change that at all in recent years?

What tips can you offer for smoothing off welds? That would probably be the most time consuming PITA part of it for me.

In the name of sharing skills lets see what ideas you have...

 

[Nudist]

A good weld that has full penetration can be ground down to near flat.... nothing a proper bondo job couldnt ease.

 

[drunkNun]

full penetration

Always a good thing. :LolLolLolLol:

 

[Nudist]

I knew someone was going to exploit that one part of it.....

 

[dogbreath]

Fiberglassing a new shape around the tank is perfectly feasible, you just have to float the fiberglass. If you fiberglass to the tank and then bolt it to the frame it will probably break.

 

[Vcook]

Are most tanks steel or stainless?

steel

 

[Candyman]

What attachment do you use to grind it down? Seein as how a tank would be kinda awkward to work on a bench grinder

 

[Candyman]

Fiberglassing a new shape around the tank is perfectly feasible, you just have to float the fiberglass. If you fiberglass to the tank and then bolt it to the frame it will probably break.

Describe what you mean by float

 

[dogbreath]

Fiberglass it to the tank and leave it. Don't bolt the glass to anything else if it's stuck to the tank.

Get an angle grinder and some steel grinding wheels to grind down the welds.

 

[fslflint]

modding tanks is a job for a good tig welder IMO. I wouldn't trust the job to just anybody.

well, steel wheels work well on welds, but with sheet metal be extreemly careful, or you will be buying a new tank.

a better option is a 4" grinder with a flap disk on it. its allot less aggressive, thus less risk.

another option and probably the safest still is a quality palm random orbital sander with an assortment of different grit disks.

 

[Dudad]

My tank is welded and im using a flapper disc to grind with........just be careful cuz that bitch will flatten a spot REAL fast......I had a couple spots i had to round out because it ground it flat lol

 

[shift1313]

one thing that hasnt been mentioned is cleaning the tank and letting it air out. IF you are going to weld to it you might want to fill it with water. This will help keep the metal cool and also help flush gas out.

There are epoxies out there that you can use for car patch panels. They are supposed to be as stron when done properly, might be a good option? www.eastwood.com should sell it.

Cleaning up the welds. If you are or know someone proficient at tig then you shouldnt have much work to do. I use a right angle die grinder with a 2" sanding disc assortment. You can start with like an 80 or 100 grit and work to a 150 then you scotch-brite pads on the same grinder to finish it off before cleaning/etching primer.

You should have no problem fiberglassing and getting it to stick as long as you prep the tank. You cant fiberglass to a clearcoated/waxed tank and expect it to stick. If you get it down to bare metal, I did this by hand on my tank but scotch brite pads again work well without heating it up to bad. You will want to rough up the metal and probably wrap the glass around every corner you can find.

What are you trying to do?

 

[Candyman]

modding tanks is a job for a good tig welder IMO. I wouldn't trust the job to just anybody.

well, steel wheels work well on welds, but with sheet metal be extreemly careful, or you will be buying a new tank.

a better option is a 4" grinder with a flap disk on it. its allot less aggressive, thus less risk.

another option and probably the safest still is a quality palm random orbital sander with an assortment of different grit disks.

Ya I have yet to use one of those flapper wheels, wasnt sure how abbrasive they were.

 

[fslflint]

they are pretty abbrasive, but they have allot less bike then a standard grinding wheel

 

[Candyman]

Thanks for the info Shift, like I said, I havnt had experience getting metal and glass to bond so I wasnt sure how succesful it would be.

I'm not really trying to do anything right now, but I'll probably end up modifying a tank eventually. Thinking possibly of bikes that require RAM intakes, possibly incorporating the intakes to go down through, or join very closely with the tank. I'd need to modify the tank somehow for that... I dunno, I have it in my mind but its hard to explain.

Something like this, though this one's scoops are just aesthetic as far as I can tell.

 

[shift1313]

if it were me i might make the parts out of fiberglass then use some sort of epoxy to mount them to the tank, then bondo over that. While you can get the glass resin to stick you would be better off using an epoxy of some sort.

good luck

 

[929_adam]

A good weld that has full penetration can be ground down to near flat....

my buddy who polishes frames told me that you can actually strengthen a weld by smoothing it off b/c you work the metal over both sides of the original seam so it spreads any would be tension across the area, making it less likely to stress or fail.

:twocents: - thats just what i heard.

but i think i would use the DA over the flapper on it.

 

[mpls|cafe|racer]

Your buddy was wrong. Once the weld has been placed and cooled there is no tension.

The way you release tension in a weld is called hammer welding, and you usually only do it on sheet. You put your weld in, be it a tack or a stitch, then you dolly behind the weld and give it a good pop with a hammer right after the weld is done and it's still hot. This will release the tension on the weld, decrease warpage, etc. It does NOT strengthen the weld though.

Neither does grinding it flat. Whomever taught him that really didn't know what they were talking about. In structural welding we only remove suface aesthetic welds. Things that are welded on the outside where people will see, that are NOT critical welds. If they are critical welds and could cause a problem at failure we don't grind them at all.

 

[mpls|cafe|racer]

Oh, and if you ARE going to weld a tank there's a really easy way to do it safely.

Start up your car or another bike or something nearby and run a hose from the exhaust to the inside of the tank through the gas cap. Let it run for a few minutes to fill it with the exhaust and weld. Exhaust does not support combustion, and works great for this.

Be cautious though... this should only be done after you've drained the tank and let it air out for a few days or a week... you'd think it wouldn't take that much but I've seen someone dump gas, wait a day, and then try to weld. BOOM! Shit sounded like a shotgun going off, and luckily he wasn't hurt.

 

[JK1]

I´ve modded a few tanks. Most difficult thing for me was to get the welds to hold the gas inside. I have both good (my car) and bad (a bike tank) experienses of sealing liquids (like POR15). Now I prefer welding the seams properly and checking them with pressure (little air in the tank and mist of soap water over the seams). I also finish the welds with solder.

J