How to mould a motorbike petrol tank

Written by chris gilliland Google
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How to mould a motorbike petrol tank
Create a new petrol tank for your bike. (Photodisc/Photodisc/Getty Images)

Fibreglass petrol tanks are in a variety of motorcycles, ranging from motocross bikes to custom-built cafe racers. Although a few of these tanks are available on the market, the determined do-it-yourself consumer can build a similar product using off-the-shelf materials. Creating the tank is done by creating a model -- or plug -- from green floral foam, which is then used to create a mould. Although this may be a slow process, using a mould to create the final product will ensure the best results. Expect to spend several days to complete this project.

Skill level:

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Things you need

  • Green floral foam
  • Spray adhesive
  • Knife
  • 220-grit sandpaper
  • Air compressor
  • Mould-release wax
  • Fibreglass cloth
  • Epoxy resin
  • Scissors
  • Small container
  • Paintbrush
  • Body filler

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    Creating the plug

  1. 1

    Select a large block of green floral foam, or glue several smaller foam blocks together, using spray adhesive.

  2. 2

    Sculpt the base of the tank first, carving the foam material with a sharp knife to fit the motorcycle's frame.

  3. 3

    Cut large chunks from the top and sides of the tank, using a sharp knife, to create a rough shape of the tank. Concentrate only on cutting the foam to right size and general shape of the design.

  4. 4

    Define the shape of the tank, using a sharp knife. Round off or square the edges of the tank and include any details as required by your design.

  5. 5

    Stop occasionally to ensure the tank is symmetrical -- evenly shaped on both sides of the tank -- and make adjustments as needed, using a sharp knife to cut excess foam.

  6. 6

    Smooth the shape of the tank, using 220-grit sandpaper. Blow sanding dust from the surface of the plug by using compressed air.

  7. 7

    Coat the plug with mould-release wax.

    Moulding the plug

  1. 1

    Prepare your fibreglass cloth and epoxy resin. Cut the fibreglass cloth to fit the shape of the tank, using sharp scissors. Mix the resin in a small container, following all directions provided by the manufacturer.

  2. 2

    Flip the plug upside down so that the bottom of the plug faces upward. Apply an even coat of epoxy resin on the bottom of the plug, using a paint brush.

  3. 3

    Lay the fibreglass cloth over the resin coat. Spread another coat of epoxy resin over the cloth, using the tip of the paint brush in a dabbing motion. Smooth out any air bubbles in the cloth or resin with a putty knife.

  4. 4

    Lay another layer of fibreglass cloth over the previous layer. Coat the cloth with epoxy resin, using a paint brush. Smooth the fibreglass layers, using a putty knife to remove any air bubbles in the resin. Repeat until four layers of fibreglass cloth are placed over the bottom of the plug.

  5. 5

    Allow the epoxy resin to cure overnight. Then pull the bottom half of the mould off of the plug.

  6. 6

    Mold the upper half of the plug following the process shown above.

  7. 7

    Remove any imperfections on the inner faces of the moulds, using 220-grit sandpaper. Fill in low areas on the surface with body filler.

  8. 8

    Coat the inner faces of the moulds with mould-release wax and create the final petrol tank, using fibreglass cloth and epoxy resin.

Tips and warnings

  • Take your time. Rushing this project will create problems that may not be repairable.
  • Don't use the polyester resin found at many hardware stores. Polyester resin will dissolve the foam plug unless the plug is covered in foil.
  • Work in a well-ventilated area to reduce the risk of inhaling foam dust and resin fumes.

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