Building a Custom XS750 Cafe Racer Seat

Right, this is a quick guide to making a custom seatpan and is no means a professional attempt, although this is really just a way to make a decent cast/ mould. The seatpan we’ve made is ok but with all the filler trying to get the correct lines etc.. its become a bit heavy so making another seat using the original as a mould should produce a better (and cheaper) seat.
If you can get a custom seatpan for £80-100 for your bike then do it as this is a bit intensive and cost about the same to build, however if anyone wants an XS750 seatpan like the one pictured leave us a comment etc.. on here and we can build one.

So getting started you’re going to need a few things:

  • A generic seat that fits the XS750 (Or whatever bike you have)
  • Fibre glass resin & hardener
  • Fibre glass mat
  • Aluminium mesh
  • Gaffa tape
  • Fibre glass filler
  • Fibre glass/plastic primer
  • An electric sander (best thing ever!) and other power tools (cutters, drills, dremel etc..)
  • Clamps
  • Sandpaper
  • Expanding foam
  • Lots of paintbrushes
  • Lots of tea, help and patience

First of all we’re using a generic seatpan that fits the bike pretty well, cost £40 but we’ve got an adequate base to work with. So we trim that down to fit the front of the tank. The fibre glass materials cost us about £60 from Halfords but you can probably get that cheaper elsewhere. You’ll need a stack of really cheap paint brushes as I doubt you’lll want to go through the effort of cleaning hardened resin off of them.

Next after taking a few measurements we know how far back it needs to be and the width at the widest point to cover the frame, also using someones arse we could see where we needed the foam to end and the cowl to start. Using some card and a marker pen we plot the measurements and draw the base curve for the rear of the cowl. Securing the pan to our template we start to cut and add the aluminimum mesh and tape to build a rough shell and surface to fibre glass on to. It only has to be rough since we’ll be using filler to get the proper lines and curves.

Now we fibre glass this shell. Few things/ steps to note with fibre glass and help you avoid the mistake we made:

  1. Cut small strips  of fibre glass mat – large strips can be a pain to keep stuck in place
  2. Too much hardener in the resin mix will produce a fast setting resin, which turns to a jelly (not great)
  3. If using a brush to apply resin don’t do brush strokes – dab it on.
  4. Apply some resin mix to the surface you want to stick the matting to first.
  5. Place the fibre glass strips on to your surface and dab some more resin on the top.
  6. The fibre glass mat should go clear-ish as it soaks the resin.
  7. Keep dabbing it to get it properly stuck to the surface – if you use brush strokes you’ll tear the mat and produce shards
  8. Try to apply a couple of layers together and then leave to dry/ cure.

Once you’ve done the basic cowl, fit the seat on the bike and check your lines. Turns out our’s was too high and needed adjusting – the beauty of fibreglass is you can cut a panel and refit it with moree fibre glass (and gaffa tape).

First attempt is too high

Kev cutting the seat down

Gaffa tape for the win!

Nearly done with the fibreglassing

After adjusting the sean pan and fibre glassing the top to get our lines right next thing was to make sure it was secure with the rest of the sat pan – so we fibreglassed the inside of our cowl and made sure it joined/ covered the inside of our seat pan. Afterall we were going to mount a light to this and it needed to be strong.

Clamping the layers together

Turns out that aluminimum mesh and gaffa tape don’t like to be fibreglassed and we had 2 separated layers of fibre glass. We remedied this by mixing some mroe resin and pouring it between our layers and then using several clamps we forced the layers together while the resin set. So we now had a rough and sturdy shell – already weighing quite a bit.

Expanding foam DOES expand!

Next we slapped on a whole tub of filler to work up the lines and curves and filled the gap between the seat and the cowl with expanding foam so that we could fix the seat foam in place. When this all set we sanded it down – however trying to sand the stuff manually is not the way forward, do yourself a favour and get an electric sander as the cost is worth the time and effort you will save – Seriously, if there is one main tip it is this one!

First coat of filler on the seat

Ok so the filler is sanded down, best bet is to leave it with someone else to do all the work – hey I fibreglassed the damn thing so make the other guy do all the sanding. So keep applying filler and sanding it to get the curves then use the plastic primer to coat and help identify blemishes – also to allow you to spray paint the cowl.

The making of the light hole is pretty obvious – cut a square out, drill a couple of holes to mount the fitting. Although the genius move is to cut the rear light lens (the red plastic bit) and mount that inside the fibreglass with some glue.

For the seat covering – see this post here (It’s the same pan): http://bikearama.com/motorbikes/seat-upholstery/

Lastly I spray painted the cowl – however I would recommend a coat of grey primer first and not leave the yellow plastic primer to spray on as it turned by midnight blue paint to a purple – still it looks pretty good.

Finished seat pan

What we learnt:

  • Aluminimum mesh and gaffa tape, although quick to fabricate something are crap for sticking fibreglass to.
  • Build a mould from scratch to build a lighter seat.
  • Fibre glass is really itchy so use gloves and overalls.
  • Its pretty itchy stuff in the lungs and eyes so when cutting it, protect yourself.
  • It took us a few weekends to produce and cost about the same as buying a seatpan (but we couldnt find any decent ones for the XS750)
  • Expanding foam really does expand more than you would expect – it also bonds to skin really really well.
  • Building seatpans is good fun and worth the effort.

So there we have it, a finished seat pan. However it weighs a fair bit because of all the filler and we’ve found that its a bit wide at the moment, so next stage it to use it as a mould to create a better pan and fixings for the the seat cover – if you want one let us know and we can sort one out for your XS750.

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