Nobody likes it, but broken bodywork is a reality with today's sportbikes. Even if you baby your motorcycle, it is bound to accumulate at least a stress crack or two due to vibration or over-tightened fasteners after even just a few years, not to mention the inevitable bumps and abrasions that stress the relatively brittle plastic beyond its flexible limits.
In the past, your options were limited to bonding broken bodywork together with bubble gum and curtain rods, or perhaps epoxies and resins that were not exactly compatible with the type of plastic that most motorcycle manufacturers use. While some shops perform plastic welding, duct taping or sewing parts together using lock wire became more common (especially on race day).
More recently, to our benefit, new refinishing products have become available to support the larger automotive industry that has found applications for plastics. As a result, repairing broken bodywork just got easier.
Typically, body panels are made of one of three categories of plastics:
*Flexible (Polyurethane and thermo-plastics primarily used on dirt bikes.)
*Rigid (Polycarbonate, polypropyleneand some types of thermoplastics. ABSfits in this category, and is commonly used on sportbikes.)
*Extra Rigid (Rigid polymer alloy and nylon alloy. Fiberglass reinforced poly-ester is frequently used on race bikes, and also by aftermarket manufacturers who are able to recycle Andrew's old suits.)
Each type of plastic requires different materials to affect a proper repair, and although you may be able to use whatever you have available, often the results are less than professional or failure prone, with cracks reappearing to spoil your fresh paint job.
Since most sport bikes come equipped with ABS (Acrylontrile Butadiene Styrene, for those of you who want to be the hit of the party), the following steps apply to these types of fairings.
Remember: Work in a well-ventilated area, and wear gloves to prevent your hands from absorbing the chemicals. Many of the chemicals mentioned can be found at auto supply shops. Look for repair kits containing the items you need rather than buying large, individual containers.
Begin by cleaning the part thoroughly. Soap and water works well, but some manufacturers recommend special cleaners such as SEM 3835 Plastic Prep, designed to lift impurities out of the pores without dissolving the plastic. These chemicals do not evaporate quickly, allowing you time to wipe it up before it dries, leaving the impurities behind. Either way, start with a good bath in soap and water. |
For minor cracks, glue the ABS using methylene chloride acrylic cement (available at a plastic supply store). This clear liquid has the same consistency as rubbing alcohol and evaporates almost as quickly. It is ideal for repairing minor stress cracks without damaging the paint or leaving an unsightly glob. (Test it first, and be sure to catch any excess that runs through the crack and wipe it up immediately.) |
The cement technique worked well to repair this tail-section that shattered when an aftermarket signal light was bolted on and over-tightened, leaving a huge hole. Aside from a few marks where paint chips are missing, you would never know that almost a dozen pieces of the jigsaw puzzle were glued back together in minutes without leaving any messy residue or buildup. |
A squeeze bottle with a needle is used to force the liquid glue into the crack. The glue doesn't fill the gap, but instead works by dissolving the ABS and then allowing it to harden again, forming a bond. The dark stains in the picture are residue from the ABS that has been dissolved by the glue. |
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It's a good idea to strengthen the repair from the backside. For this repair, duct tape was used to dampen the vibrations. It has held up for a full season of abusive riding without falling apart. A better idea is to gusset the repair by gluing a sheet of ABS behind the repaired area. |
If you are missing pieces or want a stronger repair, use a two-part filler such as Duramex 4040, Worth Plasfix or other compounds from SEM or Dupont that are designed specifically for repairing rigid plastic. |
Before filling, prepare the crack using a folded piece of 80-grit sandpaper and use the edge to file out a V groove in the plastic so there is more surface area to adhere to. Go deep enough that you are at least halfway through the material and then repeat on the opposite side. |
For filling holes, work from behind and create a new surface by reinforcing the area with a mesh such as aluminum window screen material. Before applying the filler you may want to use an adhesion promoter on the plastic. (Warm up the area with a heat gun, spray on, and heat to evaporate just prior to applying the filler.) |
Once the filler sets, apply more filler to the front to bring the new surface level. To make it pretty you can use a surface putty such as Evercoat Poly-Flex. It can be applied to a finished thickness of 1/8 of an inch and sands silky smooth. Use this for your purely cosmetic repairs. Unlike regular automotive spot putties, this stuff adheres well to plastic and remains flexible (up to a 77 percent bend according to the manufacturer). |
If you are planning to do track days and haven't scratched your bike's skin yet, hang up the stock bodywork for safe keeping while you fit up a replacement fiberglass fairing. It is much less expensive and far easier to repair.
Special thanks to Jamie Richardson at St. Boniface Arts and Technology Centre, and MPS, for technical assistance.