Retaining the factory-equipped seat is considered a major faux pas for a custom motorcycle. While the lines of these specially-constructed machines can often be considered works of art, the bulky and unattractive stock seat can detract from the motorcycle's overall appearance. To work around this, custom builders often resort to metal work or fibreglass to construct a seat pan that is better suited to the custom work. Fibreglass is usually the material of choice for most home-base DIYers, who don't often have access to metalworking tools. With a little preparation, fibreglass can yield incredible results.
- Skill level:
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Things you need
- Painter's tape
- Expanding spray foam
- Bread knife or electric carving knife
- Aluminium foil
- Clothes pins
- Fibreglass resin and mat
- Disposable container
- Paint brushes
- Sandpaper (coarse, medium and fine grit)
- Body filler
- Spray paint
Remove the stock seat, either by unlocking the seat or unbolting it from the frame.
Prepare the motorcycle by laying a sheet of cardboard over the exposed frame. Tape the cardboard to the frame using painter's tape, covering it completely. Continue to place a layer of painter's tape along the frame, gas tank and rear fender to protect the motorcycle from the fibreglass.
Apply a thick layer of expanding spray foam over the taped-off area on the frame, forming the crude shape of your intended seat pan. Allow the foam to cure for at least 24 hours. Shape the foam with a bread knife or electric carving knife once it has cured. Work slowly, carefully sculpting the foam until you have formed the seat pan to your liking.
Wrap the foam seat pan with aluminium foil. Place a sheet of fleece over the seat pan and pull it down tightly to stretch the fleece over the pan. Secure the fleece to the motorcycle's frame with clips or clothes pins.
Lay the fibreglass mat onto the seat pan. Cut the mat into shape with scissors and set aside. Prepare the resin according to the manufacturer's directions in a disposable container.
Brush a layer of resin onto the fleece with a large paintbrush and lay the first layer of fibreglass strips onto it. Dab another layer of resin onto the fibreglass with the tip of your paint brush, coating the entire layer of fibreglass. Continue to lay the fibreglass layers, dabbing another coat of resin over it, until you have built up the thickness of the fibreglass to your liking. Ideally, you should have at least three to six layers. Allow the fibreglass and resin to cure for at least 48 hours.
Trim off the excess fibreglass from the seat pan using a grinder. Pull the fibreglass seat pan off of the foam seat pan. Sand the surface of the fibreglass seat pan with an coarse-grit sandpaper to smooth it out. If the seat pan is not intended to have exposed fibreglass, install any mounting hardware and have the seat upholstered at this time.
Finish the fibreglass seat pan by sanding with a medium-grit sandpaper. Fill in any low spots in the fibreglass with body filler. Apply a coat of primer once the seat pan is smooth and sand again with a fine-grit sandpaper. Paint the seat pan and coat it a layer of protective clear coat paint.
Attach any mounting hardware and have the seat upholstered.
Tips and warnings
- Take your time. Rushing can lead to irreversible mistakes.
- Always wear gloves, eye protection and a respirator when working with fibreglass to prevent skin, eye and lung irritation or injuries.
- Follow all manufacturer provided instructions when mixing or working with fibreglass and resin.
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