One of my winter mods this past season was modifying my aftermarket undertail. It contoured the lines of the subframe but I wanted it to follow the fairings instead, giving it a new leaner look.
Before...
This is the way I did it, it may not be the best way but it worked.
1. Cutting the undertail
To match the lines of the rear side fairings the aftermarket undertail needed to be trimmed a few inches. Finding just where to trim was the tricky part. I found that by removing the stock undertail plastic (all of it) it was a lot easier to determine where to cut. Once the stock parts are removed (ECU, battery and rectifier included) you should be able to see where to cut. The cut itself is going to contour the lines of the fairings and is not a straight cut. At the end of the day I just eyeballed it. Now that I think about it a piece of string tapes to one fairing then moved across to the other side could give you a good line to mark.
2. Prepping for the glass work
Remove the subframe from the bike! I wish I had done this the first time; it would have saved me several weeks of work. With the subframe removed put the plastics back on it. This left you know exactly where things are going to and where to mark for cutting trimming later on. It also allows you to cut the glass to shape (see 3 and 5)
3. Figuring out how it's going to work.
My solution may not be the best but it worked. First I used glass cloth and placed it OVER the edges of the surrounding plastics including the cut undertail. This gives you the contour of the bottom. Stretch and shape as needed then hold in place (tape). Sort of like in the picture below but using a lot more tape to hold the sides in place. You may want to use a thin tape to protect the fairings too.
4. The first coat of resin.
With the contour you want apply the first coat of resin. Make sure you only go past the area where it meets the original undertail a few cm, same for the edges. Don’t worry about the curve at the front too much, you’re going to need to trim it anyway (that comes later). Once is dry, remove nothing! You will need to trim the sides of the hard glass flush to the side fairings. Take your time on this. Mistakes here are hard to fix.
5. The second layer of glass.
Now that it’s dry flip the thing over so you can see in the inside. Here I used glass mat, not cloth. The glass needs to be trimmed fairly accurately because it’s what’s going to hold it in place. It also needs to extend up the existing undertail a few inches (it’s what’s holding it on). Place a coat of resin on the new part and on the part of the undertail it’s to mate with, then lay the glass on top of it then coat the second layer so it’s soaked. Make sure it’s tight to joint with the undertail.
6. Things to look out for and trimming.
The visible side of the undertail is going to need some work at the joint with the original undertail. Trim what you can with scissors, blades, ect, then start sanding. Since the resin more than likely warped the cloth while drying you’ll need to use a Bondo like product to smooth it out. It also helps with the joint area. Sand it, then sand some more and when you can’t do anymore… sand some more. Looks like shite, but it worked…
7. What and where to trim.
Obviously you have to get it in and out of the subframe so you’ll need to play with it a bit to figure where to trim (have a look at the above shot again). Once that is all done it’s time to put the bike back together and figure out what else needs to be trimmed. The tip-over senor is one area and where the wire loom comes through on the right side is another. This is also were you see it maybe easier to just cut it back a bit (I did).
8. Get it painted.
Having it professionally painted made a world of difference.
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9. The other things
The battery had to be relocated. It’s now on the left side of the bike down where it’s located on the TLR. The rectifier was another item that had to be moved. With two ‘L’ brakets from the local hardware store and a tap I placed it on the subframe. The ECU and wire loom needed a new home. It can be seen in the picture with the rectifier.
10. Done.
Fun with fiberglass (Undertail).
Linear Mode
