Expanding stock tank with hot water and air??

Still waiting on the petcock. I would use the one I have but I have a race on Sunday and don't want to not have a good petcock and gasket in case the super hot water ruins the o-ring. I hope it comes in today. I am planning on doing this tomorrow night (Friday)

If you look behind the shrouds the two parts on the front each side of the frame the tank has tons of room to expand. I do not want the top or the sides at the back to expand at all.

I will post pics and comments as soon as I get the petcock. (ordered last Friday)

I tried to post pics of my IMS tank on another thread with no luck. If it doesn't work I can e-mail them to someone that knows how to reduce the size for this forum. I will let you know.


It will work. Never measured how much you gain but I have done it just for shits and giggles on my 400 in 99. Also did a conversion on a 98 CR125 that we stuffed a 500 motor in (for that I used a heat gun to shape the tank to fit the head. The motor went in with little hastle.

Boil the water, fill the tank and watch how much air pressure you use. It won't take alot. I would start with 5-10 psi to see how it does and slightly increase to get ot moving. Take your time and do it several times to get where you want to go. Don't try to get everything at one time as this will and I stress will cause disaster.

Back to the heat gun, I have used this method to increase or decrease and shape plastic in specific places and have had great luck. When useing the heat gun to increase the tank in a specific place, I also use a bit of air. It's like using a rose bud tip on the gas oxy-aecet welder to take out dents in pipes.

Thanks for the info. I think I will get the results that I want. I am not in a hurry so I will take it a little at a time. I do have a nice heat gun and planned on using it if needed. Parts house just called and the petcock is in!!! I will be doing this tomorrow after work.


:bonk::thumbsup::cry: Well I gave it a rip and had good results!!!!! :confused: I installed my new petcock and got out my ratio rite and measured how much the stock tank would hold. I got 1.82 gallons all the way to the rim under the threads. I then dumped out the water I used to measure with and mounted the tank up on the bike. I boiled 1.25 gallons of water and used a large funnel sitting on the bike I poured it in! :bonk: I thought I might have a melt down with all the hot steam!!! I was surprised how long it took the outside of the tank to feel hot, about 1 minute. I let it sit pondering if I should boil more water and use this water to only preheat the tank. I decided to add some air and see what happened. I gave it about 2 quick shots of air and Holy :thumbsup: the tank blew up like a balloon. It did not expand much at the shrouds. It expanded behind the radiator and underneath front fins which is right where I wanted it to expand. My air hose set up would not hold the air pressure longer than about 2 minutes. It was leaking at the rubber hose to the vent cap nipple. I rolled the bike out side and kept adding air trying to keep it at a constant pressure and rinsing the out side of the tank with cold water from the hose and it finally cooled off. I knew that I had gain some but was unsure how much. I drained the water out using a spare fuel line and kept the pressure up. The hot water really came out fast(under pressure). At one point it found its way into my boot!! :bonk: The water was still pretty hot!!! I pulled the tank off the bike and completely emptied it. Reinstalled and started pouring water in from my ratio rite.

The tank now holds 2.06 gallons. :bonk: This took very little effort. I have a race Sunday so I decided to call it quits for the night. Next week I will fix the air leak on my filler set up and try it all again. I am hoping that with constant air pressure I can get the water cooled off and keep the tank around 2.2 gallons. I inspected all around the tank and it is not even close to rubbing on the frame or anything else. I am stoked to try again and know I will get to 2.2 gallons with out a problem. The tank still feels nice and solid and not thin at all.

This was way easier than I thought it would be. Trust me I was a little nervous with the pot of water right off the stove!!! I used a sweet funnel. I would strongly suggest that if you do not have a high flow good stable funnel to not try this!!!!

I will post my next try next week and let you know if I get to 2.2 gallons

Thanks for the comments

There wasn't really any reason to take pictures so I didn't.


Can you post some pics so we can just see it because I can barely make one ride with my tank right not and it would be nice to get another .3 or .4 more gallons.

Wow that is awsome it worked:thumbsup:

You sure did get a lot of extra gas too:ride:

Nice! I was curious how this would work out for you.

That is awesome. I would have lost that bet. Unreal. :thumbsup::confused::thumbsup:

Damb thats sweet!!

Can you post some pics so we can just see it because I can barely make one ride with my tank right not and it would be nice to get another .3 or .4 more gallons.

Nvm I looked there is no room to expand. How much is a tank that is like 2.8-3 gallons on ebay

Post some pics for sure. :thumbsup::thumbsup::confused:

Sap- glad to hear it turned out good. Where in WA are you? I'll bring my bike by and let you give it the treatment... I'll buy the beer and still be way cheaper than a Clarke! :thumbsup:

Nice job man! :thumbsup:

Nvm I looked there is no room to expand. How much is a tank that is like 2.8-3 gallons on ebay

I paid 164 for a Clarke 2.8.

I like the natural see through color though. I can tell how much gas i have without stopping to look.

I might try this expando method with my XR tank.

I've got my fuel mileage figured out pretty good. It is any where from 22.7 to 25.8 depending on what kind of terrain that I'm riding. Most of the enduro and harescramble stuff i do is max 30 miles between fuel stops so I like to use the smaller tank for that. The reason I did this is that even though the stock tank holds 1.85 gallons you will never get 1.85 gallons out of it before you start to hick up and burp. I always deduct about .3 gallons before I calculate how far I can go on a tank of gas. If the tank holds 2.2 gallons and my mileage for that kind of terrain is 22.70 I figure that I can only effectivly get 1.9 gallons out of the tank that gives me 43.10 miles before I start to hickup. If the laps are 7 miles than I know I have a max of 6 laps and I need to pit for gas. In a ten lap race at 7 miles with a 3.1 gallon tank using my .3 deduct leaves me 2.8 gallons at 22.70 MPG I would have to stop and get gas max of 9 laps. So it is still a one gas stop race. I can stop and splash in 2 gallons and ride faster with the smaller tank 6 laps in a row than if I was to use the large tank and carry 8 pounds more gas around so that I can make it to lap 9. I would still have to stop for gas so why carry all the gas around for the whole race and have the shrouds 2 inches wider if you still have to stop for gas. I also like to stop around the 6 lap point so I can get fresh goggles with a new stack of tear offs!!

Any way sorry to ramble on.

There really isn't any thing to see if I took pictures you can hardly tell that the tank holds more fuel.

For those longer casual rides in the mountains in the summer I will use the IMS tank just to make sure. It is not uncommon for a mountain ride to be in the 60-65 mile range.

This was very easy to do.


I was just thinking. Have you re-checked the volume of your tank since you expanded it. Reason I ask is that some plastics have a memory and will try to return to there origional shape. Your tank may try to shrink back on you over time.

I work with plastic Vacforming vendors. They have to make the tools oversize because the plastic will shrink once the part is off the tool and cools.

Its cool that you got it to expand where you wanted it to. I would of been nervious of having scalding hot water exploding in my lap.

I am working on making a better air fitting and I am going to try to get the tank to 2.2-2.3 this weekend. I am sure that it will shrink slightly from the size I get it to so that is why I want 2.3 if I can get it. If it shrinks back to 2.2 and you use my .3 gallon reserve then that leaves me with 1.9 gallons that I can use every race. I would be happy with that.


Do you have any pictures yet?? This is something I will be trying in a couple of days from now. Have you tryed again for 2.3 gallons? I really don't like the ugly Clarke or IMS tanks, too bulky. Plus, 2.3 gallons is all I really need.

no pictures. There is not much to see. I have not had time yet to try it again. I spent 3 days last week in the hospital with a bowel infection. (not fun!)


no pictures. There is not much to see. I have not had time yet to try it again. I spent 3 days last week in the hospital with a bowel infection. (not fun!)


:thumbsup: That sucks. Have you dropped a bunch of weight because of the infection? LOL

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