Custom Gas Tank on a Motorized Bicycle




Introduction: Custom Gas Tank on a Motorized Bicycle

About: Full time College student (Computer Science and Engineering Major) with a passion for building stuff with whatever is on hand at the time. Been tearing stuff down and putting it back together my whole life. ...

Seeing that Instructables had a bicycle contest, I knew I had to enter the contest with this project. It took two weeks to get the materials and put it together. So here is the results.

I bought a motorized bicycle kit about a month ago and I did not like the look of the cheaply made tank that comes with all the motorized bicycle kits. They use cheap metal and when I received the kit, the gas tank had a little bit of rust inside and had a dent on the side of it. The petcock that comes with it also leaks and the inline fuel filter sucks.

So I decided to make my own tank using fiberglass, styro-foam, epoxy resin, and wooden dowels. It is simple, but time consuming to make a custom made tank as shown in the following steps. I tried to use wire mesh as a base for the tank, but the shape I made had too many curves for it to form.

Do Not use the green styrofoam that I show in the pictures because that foam does not dissolve with any solvents.I planned to use Acetone to melt the foam after the fiberglass was laid, but ended up cutting a hole in the fiberglass and removed the foam with a dremel and then patched it.

This instructable involves using dangerous tools and chemicals. Safety should be your number one priority

Video Walk Around of Tank

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Step 1: Materials and Tools

There are many materials and tools used in this project. It can be very expensive to build your own tank, but it is worth it in the end because no other motorized bicycle will have the same tank.

  • Styro-foam
  • Small Wooden Dowels
  • Styro-foam Safe Glue
  • Fuel Safe Epoxy Resin 
  • Fiberglass Cloth (2-5oz)
  • Fuel Spigot
  • Inline Fuel Filter
  • Cardboard
  • Masking Tape
  • Marker
  • Spray Paint for Finish
  • Clear Coat
  • Primer
  • Copper Sheet
  • Copper Coupler
  • Removable Plug for Coupler
  • Flux and Solder for Copper
  • Thread Lock (Optional)
  • Scrap Piece of 1/8th inch plywood
  • Body Filler (Bondo) 
  • Dust Mask (highly recommended)
  • Gloves
  • Measuring Cups
  • Four nuts and 2 threaded rods.
  • Acetone

  • Bandsaw
  • Rasp
  • 320 Sandpaper
  • Socket Set
  • Gloves
  • Spreader
  • Propane Torch
  • Razor Knife or Sharp Scissors
  • Tin Snips
  • Drill with Drill Bits
  • Scroll Saw (Optional)
  • Scotch-Brite Pad
  • Sanding Disks
  • Dremel with Sanding, Wand Attachment, Brass Brush, and Cut off Wheel

Step 2: Designing the Tank

I thought the space between the three bars before the headset was a waste and thought that it would be a perfect space to put a gas tank. I debated on whether to put the tank on the top bar like a regular motorcycle and blend it into the frame or to use this "wasted" space as my gas tank. The size of the tank is approximately the same as the stock tank that came with the kit.

After removing the stock tank using the correct sockets, I held up a piece of cardboard to the area that will be the tank. I used a sharpie to create the profile of the bottom bars. Then I held it in the same position and copied the profile of the top bar using a sharpie. I then cut the shape out of  the cardboard out using a razor blade. 

Step 3: Creating the Form

The form for the gas tank is made of the green foam that you can pick up at arts and craft stores. The foam is the type that you stick artificial flowers into as a base. I don't recommend using it if you don't want to cut a hole to remove the foam. Styrofoam is the only foam I know of that dissolves with any solvent.

You need to glue these foam blocks together and use masking tape in order to put pressure on the pieces being glued together.  You then stick some dowels into the form to further strengthen the foam. After the glue has dried, remove the masking tape and then take the cardboard template you made in the step before and draw the pattern onto the foam using a sharpie. 

Use a bandsaw in order to cut out the basic shape. Make sure your table is level on the bandsaw or else you will end up with one side of your tank being a little larger than the other. Cut just outside the line you made so that you can use the rasp or 320 sandpaper to hone the material down to the shape you want.  The dowels in the foam will cause a little resistance when you reach them while cutting. 

I then found the center line of the tank on the part that will be the top. I wanted to make a tear drop style tank so after measuring 1 and 1/2 inches on each side of the center line at the rear of the tank, I used a straight piece of cardboard and created a teardrop shape starting about 4 inches from the front of the tank to the two marks on the back of the tank. I then used a bandsaw to cut these two lines to create the teardrop shape.  Before sanding, it looks like a coffin as viewed from the top.
Your design for the tank as viewed from the top will be different then mine depending on the style that you want to achieve. 

After the basic shape was cut out, I used a sanding block with 320 grit and a rasp to shape the tank as I pleased. You will need to make the foam a little smaller than the final tank due to the fiberglass cloth and epoxy resin. Since my tank is inside a void in the frame, I had to make sure it was small enough to fit after the tank is created. 

Remove the wooden dowels from the form after the foam has been glued securely

Step 4: Fiberglassing the Tank

This is the main part of this instructable. It is also the hardest. It took me 3-4 days to fiberglass the whole tank with two layers of 2 oz cloth and 6 hour cure time epoxy. I put 5 oz cloth as a base on the top and bottom of the tank and found it too hard to mold to this shape. 

I can not tell you step by step on how to do this part exactly because everyone will have a different shape. All I can tell you is the best method for applying the fiberglass and some tips on how to apply it.

Using a sheet for an area is not a good idea as it will cause air bubbles in the fiberglass. The best method is to use strips of fiberglass cloth and lay them side by side. You will have to sand the fiberglass and epoxy down so having the strips overlap is not a problem. 

First thing you do is lay many sheets of newspaper down on your work surface. Next thing you need to do is get your measuring cups (I took some medicine cups from work so the epoxy measurement is accurate) and you need some stir sticks. Then you need to put on some gloves and put the foam form onto the sheets of newspaper.  

I mixed the epoxy 30cc's (about two tablespoons) at a time. 15cc Resin and 15cc Hardener. After stirring the solution, you will pour it directly onto the form. Spread the epoxy using a gloved hand or a spatula and then lay the fiberglass cloth that you cut into strips onto the epoxy. Keep pressing the cloth down onto the resin till it is completely saturated. It is better to have too much epoxy on the cloth than too little so if you think it is not saturated enough, then add some more resin on top of the cloth. If you have too little epoxy, then an air bubble will form and you will have to sand it out and replace the cloth. 

The corners of the tank need the most reinforcement than any other part. The back of my tank was the hardest part because of how small it is and the curves. For this part, I had shred the 2 oz cloth into strands and poured epoxy onto the form at that corner. I then added the strands into the epoxy so that the epoxy has some strength at that point. It helps seal it since a cloth will not fit that part. 

Between each coat (about 6 hours dry time), you will need to use a sanding disk on a drill to sand down any high points or any air bubbles that can develop. Make sure you wear a mask because the dust will irritate your lungs.  

After I did two coats, I added the gas filler neck that I created out of copper. To do this, I had to drill a pilot hole and make it into a 1 inch hole in the gas tank where I want it and where it will fit when it is on the bike. The copper sheet that is solder onto the coupler is a base that will be sandwiched between layers of fiberglass. So after making the 1 inch hole, I put the filler neck into the hole. I adjusted the copper sheet as necessary so it will fit flush against the tank. I then pour epoxy onto the base of the filler neck and added strips of fiberglass cloth. 

Make sure the tank still fits in/on the bike the way you want. 

Step 5: Creating the Filler Tube and Mounting Hardware

Even though copper is expensive; it is very easy to work with. For the filler tube, I used a 1.5 inch to 1 inch copper coupler and a sheet of copper I had left over. The cap is a 1.5 inch plug with a wing nut to compress a piece of rubber against the sides of the copper coupler.  The wing nut is replaced with a twist knob. 

Creating The Gas Filler Neck-
After using tin snips to cut the scrap copper sheet into a 3"X3" square; I put the piece of copper sheet between two 1/8" pieces of plywood. I taped the "sandwich" together using masking tape and then used a sharpie to create the outline of the 1 inch side of the coupler in the center of the "sandwich". I drilled a small hole in the center of the sandwich and used a scroll saw to cut the outline. You could use a drill with a 1 inch bit to create the hole, but I thought that it was easier and neater to cut it with a scroll saw.

The piece of copper that you remove from the plywood is the base of the filler tube. To hook the base to the coupler, you will need to sand the parts where each piece will be soldered. Then use acetone to clean up the dust from sanding and any residue that is still present on the pieces. Use a brush and put some flux onto the joint that will be solder. Place the pieces onto a brick and heat them up using a blow torch. After you have heated the pieces up enough, remove the torch and start feeding solder into the joint. It should flow easily into the joint. Repeat as necessary until the joint is completely sealed.

Use a scotch-brite pad to clean up any residue and make the copper piece shiny. =)

Mounting Hardware-
The mounting hardware is just a piece of copper about 3/4" wide that wraps around the two bottom bars. There is a hole drilled in the copper between the bars so that you can put a threaded rod through it to reach the nuts epoxied to the bottom of the tank. As you tighten the nut on the threaded rod at the bottom of the copper, the copper will bend causing it to tighten around the bars. This is the best way in my mind to secure the tank to the frame without drilling into the frame or showing how its mounted.  

Step 6: Inserting the Components and Removing the Foam

Making the Filler Hole-
After the tank is completely fiberglassed, you will need to put it on the bike in the position that it will be and mark the hole for the filler neck with a pencil. Drill a small pilot hole into the foam and then use a dremel to slowly grind the fiberglass to the needed size.  Wear a mask for this part because fiberglass is bad for your lungs.

Removing the Foam-
I was going to use acetone in order to dissolve the foam after I installed the filler neck. This did not work out because the green foam DOES NOT dissolve with any solvent. I even tried using a steam cleaner to remove the foam. I found that styrofoam is the only type that dissolves with any solvent.

So in order to remove the foam. I cut a little "door" in the front of the tank and used a dremel with a wand attachment and a brass brush to clear out the foam. I had to switch out the brush for a sanding drum a couple times because the epoxy had filled up the holes that the wooden dowels had formed. 

After vacuuming the material out and blowing it out with a compressor, I used epoxy on the inside of the tank in order to seal the little bit of foam that was left over so that it won't end up in the carb of the motor. This also helps seal any of the air bubbles that may have formed on the inside of the fiberglass. 

To installed the spigot, I drilled a hole and threaded the spigot into the fiberglass. I put masking tape over the end of the spigot that is inside the gas tank and epoxied the fitting into place from the inside.  After it was dry, I decided to fix the hole that I had to make to remove the foam. I used a slightly larger piece of heavy fiberglass cloth and epoxied it to the piece I cut out. I then allowed it to dry and carefully shoved the piece into the tank so the heavy cloth will bond to it on the inside. I put epoxy onto the area needed to seal the hole and placed the piece in place. I then used a brush through the gas filler hole to push the cloth onto the epoxy. After it was soaked, I allowed it to dry. The area around the spigot will need to be sanded a little to blend into the rest of the tank.

Gas Filler Neck-
To insert the Gas Filler Neck you created in the previous step, you will need to cut the 3"X3" base down so there are two flaps left. Insert the neck into the hole you made for it and use epoxy on the flaps to glue it to the tank. Then I laid fiberglass cloth on the flaps to sandwich the copper sheet in between two layers of fiberglass. This area will need to be sanded to blend into the rest of the tank.

Mounting Hardware-
For mounting hardware, I used two threaded rods, a couple nuts,  and a hand made bracket. I epoxied one of the nuts onto the bottom of the tank towards the rear of it, one towards the front, and used a wooden dowel to keep epoxy out of the threads.

Step 7: Finishing

The finish can make or break the look of you project. Painting and sanding any project takes a long time. Sanding  and painting my tank took about 2 days.  You need to paint the fiberglass because epoxy can break down when exposed to sunlight.

Body Filler-
Body filler is the best method for smoothing out the fiberglass and epoxy. I covered the whole tank in a thin layer of body filler and allowed it to dry. I then sanded it down to make the piece smooth. Any small dips and small scratches on the tank can be seen easier by spraying some primer onto the tank. To fill the small scratches and dips in the surface, I used some finishing putty. Of course I had to still make sure the tank still fit in the position I want it. Take the gas cap out and fill the gas filler neck with masking tape so paint will not enter the tank.

Priming And Painting-
After applying the body filler and sanding it smooth, I sprayed two thin coats of primer onto the tank. I then sprayed 3 thin coats of flat black spray paint onto the tank. Doing thin coats will help eliminate paint drips and over spray. Since gasoline is a solvent, most spray paint is not gas resistant and will be stripped from the surface. So to keep gas from dissolving the paint, I bought some automotive clear coat from a local shop to seal the paint from damage.

Putting Tank onto Bike-
After letting the paint and clear coat cure, cover the tank in tape in areas that may be scratched when installing the tank. Damaging a fresh paint job is the worst thing that can happen when your so close to finishing. Also apply tape to any area on the bike that will come in contact with the tank. Put the tank into the position you want and secure it to the mounting brackets that you made. After you are sure it is secured, remove the tape and install the fuel line. 

Fill the tank with a tank sealer because the ethanol in gas can eat through epoxy and fiberglass. You do not want that stuff in the carb of your motor.

Fill the Tank and your ready to ride.

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4 People Made This Project!


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16 Discussions


8 years ago on Introduction

Another thing that is highly recommended is to use a product from POR-15 called US standard tank sealer because the ethanol in gas can eat the epoxy and fiberglass. I only found out today and placed an order for this product.


3 years ago

Ohmigod. That's the tank I've been looking for! You should get a patent and get some manufacturer to make those. (and good luck because I think that Big Oil controls the entire Corporate landscape, and COULDA put that out years ago. Seriously love it- I might like to see it just a bit thinner and smaller, but I've searched regularly on ebay and the net for years to find a plastic tank that fits in the crux of a modern cruiser, and/or one that hangs under the top tube of a diamond vintage frame and that would save some weight too!


8 years ago on Introduction

Nice. I will be doing the same for my motored bike


8 years ago on Introduction

Cool. You do great work. I'm looking at building one of these for my son's, where did you come up with the motor set up?


Reply 8 years ago on Introduction

- got my motor kit from before they raised the price. It was $180 shipped and now they sell them for $230 +shipping. You can probably find them cheaper on ebay or from another supplier.


8 years ago on Introduction

Great 'ible'. I have one of these motor kits and the gas tank rusted in just a year. So I will use your creation to make a contoured one for my bike. I was thinking about somehow using pvc pipe painted to the same color of my frame and making it look like it was part of the frame as a fuel tank.

If I can use a large enough diameter it would hold more than a gallon. So out to the shop I go.


Reply 8 years ago on Introduction

Sounds good. Need to seal the tank. I made the mistake of not venting the gas cap and the side of the tank collapsed.


8 years ago on Introduction

Great instructable!

I might make a tank using this technique.

Too bad i wasn't able to join the contest, i'm making a custom chopper motorbicycle but can't enter now =(


Reply 8 years ago on Introduction

Thanks. Glad you like it.

You can always work on the instructable for your chopper motorbicycle and then decide if you want to publish it if you see a contest prize you want and have a chance at getting.

I hope to see the chopper when your finished.


8 years ago on Introduction

very nicely done, I was going to mention that gasoline has bad effects on fiberglass but you covered that in your comment, you may want to add it as a step to your ible though


Reply 8 years ago on Introduction

I used a "fuel safe" epoxy resin called Z-POXY Finishing Resin. I have used POR-15 products on a car restoration and loved it. I figure its better to be safe than sorry to seal the tank because I don't want two weeks of work to go down the drain.

Kaptain Kool
Kaptain Kool

8 years ago on Introduction

Cool, about a week ago, I bought an engine for my bike that looks just like that one, Great Job.


8 years ago on Introduction


Thanks for sharing this instructable.