Make/mold a fiberglass full fairing?


Been Around the Block
So I was at the cafe racer festival this weekend in France, incredible event... and I got so much inspiration from the official manufacturers prototypes there,
The Yamaha Yard Build by autofabrica was astonishing...

So this gave me the idea to create a full, one piece fairing for my FJ600 Cafe racer, that will go from the headlight all the way back to the seat, (see picture and sketch below)
This will be extremely difficult and to be honnest I'm not sure I will be able to do it...
My question is: how could I make a mold for fiberglassing such a huge fairing?
I think that the tank itself will be part of the mold, especially on the top and the rear: I will fiberglass over the whole tank so the end product will fit over the tank like a glove.
But how will I be able to do the side and front fairing part??

I though of using very thin 1mm thick steel grill, that I should be able to bent like I want? or maybe using some heavy duty cardboard?? do you guys have any ideas or tips ?

Here are pics of my current FJ600 Cafe racer and the fairing project:




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For most things, in order to make a mold, you first need an original from which to make the mold. On the whole, there is only one reason to wish to make a mold in the first place; You wish to make more than just the original, which means copies. Happily, it is quite simple and easy to create an original - at least when compared to making the mold(s) and copies, especially if the shape is complex like what you are considering.
Of course "simple and easy'" largely depends on who you talk to, and everyone will have their own version - if you are familiar with working with clay or plaster, that is easiest, if you like to weld maybe steel or alloy is easiest. If you do not have a speciality already, I suggest rigid foam and fiberglass composite.
The process is called moldless construction, and if you have some model making or construction experience likely you will find it straightforward. Having a stylist's eye for creating the beautiful flowing shape you may have in your head is another matter, but this process is far better than most for being infinitely adjustable, adaptable - changeable on the fly so you have a much better chance of getting what you want than many other materials.
The basic process is simple enough. You take blocks of rigid foam and glue them together into a larger than the approximate shape of what you want and carve it into the shape you want. Cover the shape with fiberglass, sand smooth and paint. Voila! Of course for a complex part like you have in mind will take a bit more doing than that, but the process is the same. There are urethane foams of any density you like created for this very purpose, but while superb to work with they are also quite expensive. But there are much cheaper alternatives. Green florist's foam works just fine, but it is fairly wimpy structure-wise so if you have slender elements that will have to support bigger portions you may have to create some sort of temporary supporting framing from wood or metal while you work. It is ridiculously easy to carve and shape, and because it comes in blocks intended to stick flower stems into, may not be the optimum foam - it is very easy to find though. A better choice is urethane foam insulation, which comes in 4'x 8'+ sheets in most any thickness you like. This is something bought from a commercial supplier - have never seen the equivalent in Home Depot, etc. It is always tan/gold color in my experience. You want urethane foam because most other foams melt from the solvent components of the resin you will use. Speaking of which, I heavily suggest you use epoxy instead of polyester resin. It is a LOT more expensive than polyester, but is also that much superior in every way. Use fiberglass CLOTH of the lightest weight you can get. Easier to work with. Don't fool around with carbon fiber or Kevlar or anything else. Most people (even those that make beautiful looking parts) do not make lighter or stronger parts from carbon and it is much harder to work with in this technique than glass.
You can do this job right on the bike - but you have to cover it completely because the process is pretty messy. Thin plastic sheeting like body shops use to mask off whole cars and aluminum foil and masking tape will do the job. Make an armature to support your foam, or carve up the underside so it sits right on the bike. You can use construction adhesive, epoxy, I've even used Bondo - whatever you like to glue the foam blocks up around your bike. When you have enough volume, you can start carving. Insulation foam and florists foam are crazy easy to carve. A wood block with #36/40 grit sandpaper files it down so fast you have to be careful not to over do it! Switch to #80 when you get close. You can also use hack saw blades, craft knives, wood rasps, sureform planes, Bondo files, anything you like, the foam is very soft. You want to take an extraordinary amount of time to create the EXACT, PERFECT, FLAWLESS shape you are after. It is super easy to make the foam smooth, flat, curved and perfectly fair. Once you apply the glass it will NOT be.
When you think you have what you want, mix up some resin, paint the area you want to cover, wet out a small, cut to size and shape piece of glass and squeegee into place. Repeat until your whole project is covered. This is basically like paper mach'e in principle. As long as your patches of cloth overlap, and a second layer overlaps in a different spot from the overlaps in the first layer, you can consider the strength of the end result to be uniform with no weakness ant any join. If you end up with what yo want for shape and structure, all you have to do is block sand the result, then fill the weave of the cloth with resin thickened micro-spheres or any other preferred thickener. Sand smooth and finish like any other bodywork/painting project. The good news is that if you don't have the shape you want, it is only a matter of hacking off what you don't like, adding more foam if needed, shaping again and reglassing. repeat until you are happy. There is a lot of info out there on U-tube - look at fiberglass boat repairs for starters.
You can make extremely complex and detailed shapes and you can make any adjustment or change you like at any time as there are mostly no structural considerations. If you cut a floor joist 6" too short, you have to start again with new lumber, but with this process, you simply glue on another 6" - it is nearly impossible to screw up where you can't easily recover.
Below is a picture of a seat I made this way. I was out of commercial foam and used florist's foam from the local craft store. You can see the green through the glass. This was a very complex part and had a lot of iterations adding all the features and adjustments, along with embedding threaded plates for mounting hinges and the like, but each portion on its own was pretty simple. They only had small blocks of foam, and you can see the joints between the blocks. The other thing is, it is quite easy to remove the foam and then sand and fair both sides of the end result. The seat here is not finished, but is well along the way. I added a shot of the end result. The entire part only weighs a few ounces and is very strong.
Obviously there is a lot more to this, but a reasonably thoughtful and determined person should be able to get a pretty good result if the think ahead and take their time. It really is as simple as it sounds!


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Hi Mobius,
Wow, thanks a lot for this very detailed explanation, this will definetely help me A LOT,
I think I misused the "mold" term, what I had in mind was an original creation like you are mentionning with the foam and not a copy indeed.
I think the florist foam method will be the way to go!
What I had in mind first to build a kind of "structure", from thin metal parts and apply fiberglass on it, but it would have been extremely difficult to get both side perfectly even.
Now that you explained me all of this, I think I will use foam as much as possible, I did not think foam was so easy to carve!
The best solution for my all-in-one fairing will probably be to stick foam directly on the fuel tank, carve it so the fuel tank part looks nice, then maybe create a small metal structure going up to the front headlight to stick foam blocks onto it, then carve everything, I might even be a able to mount some temporary supports on the forks tubes or triple clamps so the foam can rest onto it.
The tricky part may be the "junction" between the foam and the stock fuel tank. As mentionned above, I want the fiberglass to have the exact shape of the tank on the top, so I can just lay the fairing on the tank and the stock tank will completly disapear under the all-in-one fairing. But hey I guess I will how it works out with foam.
Thanks also for the suggestion on the fiberglass cloth and resin, I will go with the lightest fiberglass clotch I can find!

Your custom seat looks incredible!! there is no way I could tell the final product has been made this way, the cowl looks so perfect and simitrical it looks it was molded in a factory!

Too bad I have to wait to receive my new clip ons bar before I can model everything on the bike as the position of the bars will determine the holes in the fairing, but I'm already going to order a ton of florist foam blocks :) any kind of glue will do the job to stick the foam blocks together?
Thanks again!
The idea of making a cover for the tank that will largely support the fairing sounds like a good idea. You could stretch some plastic (like a garbage bag) smoothly and carefully over the tank and have a really good fit. Fit up some foam along the sides with either some temporary support or even hot glue and do a layer of glass over the tank and onto the foam to get a supporting base started. A little pre planning will go a long way, but once you have a starting point you can always cut away what you don't like later. Getting as base to work off of is sometimes a bit tricky, but the beauty of this process is that it is easy to create temporary portions that you intend on removing later. The downside would be damage to the paint on the tank down the road as grit will tend to get in between and grind on the paint. Sort of like a tank bag that you leave on the bike all the time or a bra on a car. You could also support the front of the fairing with some extra foam blocks, build the whole thing and cut the blocks off when you have it complete enough to remove from the bike. You could then remove as much inside foam as needed to make a structural mount to the frame and add lights etc. You can use anything you like (that works) to glue the foam blocks together. It is a good idea to try to just put a blob of glue in an area that you won't cut into, as the glue is usually harder than the foam, and when you try to shape contours over the joint, the harder glue tends to make a ridge that stands proud of the contour. not a real problem as after your first layer of glass, you can block sand the shape fair and the problem disappears.
The plastic bag over the tank is a good idea! I though of wrapping the tank with 3 or 4 sheets of saran wrap in order to protect it and be able to fiberglass over it and even stick some foam blocks directly onto the tank which will make thing easier.
However I didn't about starting to fibeglass the tank first, to use this as supporting base for the side and front fairing! I though of doing all the fiberglassing at the same time but this is a great idea!
I think that wrapping the tank in several layers of saran wrap should protect it enough from fiberglass scratchs?
Another idea I had for the front part was to have a lot of metal (or even wood) sticks mounted on the fork tubes and pointing outwards so I could just put the foam blocks onto them, guess I'll try many ways and see what works best :)
I've already ordered 20 small blocks of florist foam and a can of neopren glue spray :)
This was what I tried to do with few carboard pieces before posting here to give you and idea ;D

Hum... looking at this picture again I'm thinking... would it be a crazy idea to make an all-in-one fairing/tank/seat & seat cowl piece ?! ;D
I mean just imagine if the whole bike was only one fairing piece... absolutely no junction between the headlight and the seat cowl, just one huge fairing with integrated seat?!! this migh be even more difficult and the seat part could probably be made and added after the front part is finished by sticking it with fiberglass to the front fairing...


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Very nice looking XJ to begin with! Keep the thread updated on your progress.


Sent from my LG-H873 using Tapatalk
Started to prepare the bike and see what I Can do with the foam, this is gonna be more diffucult than expected ;D


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Ok so I'm starting to have something that looks a little bit like à fairing!!!


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Well I'm not making any changes to my basic cafe XJ so I'll bé able to Swap from the naked and faired version just by poping on or off the fairing and swaping the headlight :)

Maritime said:
Cool. slop on some bondo and sand, sand, sand and you will be able to glass something up!
Some bondo ? You mean I can't Glass directly on the duct tape ? But have to put something in between??
Oops I didnt know about that step ;D
Well you can go directly on the duct tape, but you'll end up with having to bondo/fill the end product a lot more. the smoother the mold the smoother the final glass product and less filler needed at the end. If you fill over the tape, sand it smooth, prime it, you can put mold release wax on it and make pulling the final glass product off a lot easier and smoother. If you don't want to do that, I've used a couple layers of aluminum foil over the tape. The glass sticks to it instead of the tape and makes it easier to get the glass off after cure, then you can sand out the foil after.
Hum that's really nice to know thanks!
I though I could just glass it and sans the imperfections on the Glass later on.
I now have to find how you call that bondo filler on french to find it on stores here lol.
But I'm afraid of the gigantic quantity I'll need seeing how huge thé fairing is.
But the aluminium foil sounds great toi, but I guess it won't smoothen imperfections like the bondo dors.
This may sounds stupid but could I use plaster like they use on walls instead of bondo? I'm thinking it may be way cheaper and easier to find, but would it be easy enough to work with? especially to sand?
Remove ALL the duct tape. The idea is to create the EXACT thing you want purely out of the foam. The foam is super easy to carve and shape, though this works against you in being very easy to damage as you work. Don't use any bondo either as although it is easy to sand, it is super hard compared to the foam and you end up grinding away a lot of foam around the bondo ruining the shape. if you have small cracks or joints ignore them as the glass will span over them. The vital thing is to have a very precision shape out of the foam so the glass will take on this shape. You will be able to do body work on it after you have the shell made up in glass, but make every effort to have it perfect in just the foam. Once you have a couple layers of glass on it, you can easily carve out the foam from the inside. You can either remove all of it, or create an interior shape and then glass over that. The foam is quite light, and having some in an interior void will vastly increase the strength and stiffness of the end product. Once you have this done you can add mounting points by glassing in some brackets. I commonly use aluminum plates with threaded holes to bolt to.
If you can't get your foam perfect as Mobius said, you CAN fill it. However, duct tape is not a good surface to lay up glass on. Use packing tape instead to cover any areas of porous material, and get it as smooth as possible. In fact, I cover just about anything foam related that I use as a plug for fiberglass in packing tape. It is easy to apply release wax to and allows for easy removal of your final part from the mold.

Depending on the shape of your mold, you may actually NOT be able to remove the plug afterwards and may need to dissolve the foam with acetone.
Dang... I used a lot of duck tape because it is part of thé structure. I have a lot of very tiny foam pieces and I'm having a lot of trouble gluing them together so I can't imagine taking the duck tape off.

Can I just add a lot of packing tape over the duck tape then apply some release wax? I just bought some release wax.

Glassing aluminium bracket is an awesome Idea too !

Packing tape is that clear transparent plastic tape right?
tahitianrider said:
Dang... I used a lot of duck tape because it is part of thé structure. I have a lot of very tiny foam pieces and I'm having a lot of trouble gluing them together so I can't imagine taking the duck tape off.

Can I just add a lot of packing tape over the duck tape then apply some release wax? I just bought some release wax.

Glassing aluminium bracket is an awesome Idea too !

Packing tape is that clear transparent plastic tape right?

Yes. I dont see why not. But keep in mind that the straighter your mold is, the straighter your part will be.

You can always glass/epoxy over glass, but be sure to rough the surface up very well (80-120 grit) and clean it with acetone or similar. Epoxy does not bond well to smooth/glossy surfaces.
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