TOOLBOX BY: DAVID STARK
TIPS
REPAIRING COMPOSITE MOTORBIKE PARTS
RS 125 Seat - Before:
This RS125 tail section was repaired using the techniques and materials in this article.
Fiberglass gas tanks, fenders, belly pans and fairings are on virtually every motorcycle at an AHRMA event, off-road or roadrace. This means almost all vintage or modern competition motorcycles have at least one composite part that will need maintaining, repairing, or fabricating. The techniques and tips in this article are based on 20 years of experience fabricating, maintaining and repairing composite seats, fenders, fairings and belly pans for vintage and modern racing motorcycles and teaching and sharing those skills with other AHRMA racers. My personal mentor is an FAA-certified aircraft mechanic, inspector and instructor who has owned and maintained composite sailboats and aircraft for more than 50 years. He’s also an AHRMA racer who has fabricated and repaired parts (including entire gas tanks) for his roadracing and trials motorcycles. (Thanks for the lessons, Dad!) As with other fabrication and repair work, such as welding, painting and machining, there are many philosophies and techniques as well as favorite products. The tips and techniques in this article are not the only way to work with composites and we welcome input from the ARHMA family about how you approach designing, fabricating and maintaining your composite parts. A composite part is simply a component that consists of different materials. For this article, “composite” refers to motorcycle parts made from a combination of fiberglass mat or cloth and the adhesives that hold the part together. Successfully working with composites requires two skills shared by painting and welding: safety and cleanliness. The catalyzed adhesives we use are toxic and prolonged exposure 32
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can be fatal. Residue from sanding composite parts creates dust that, at a minimum, will irritate exposed skin and, more ominously, may have dangerous consequences if inhaled. We ALWAYS wear nitrile gloves when handling resin and catalysts and wear a respirator and protective clothing when cutting or sanding composite parts. This is particularly important when working with carbon fiber parts. Oil- or gasoline-soaked composite parts are difficult, if not impossible, to repair correctly. We use a variety of solvents including isopropyl alcohol and Coleman lantern/stove fuel to clean parts before starting a repair and immediately before applying new cloth and epoxy. The Coleman fuel is inexpensive and will not leave residue that will contaminate the epoxy. Our molds also get a quick wipe down with one of these liquids. In this article, we’ll focus on using fiberglass cloth and “epoxy” adhesives. We have successfully used these materials for years and they work great for vintage motorcycle parts. The strength, flexibility and durability of a composite motorcycle part comes from layers of either mat or cloth working together with an adhesive. Too much, or too little, of any component can make the part heavy, brittle, inflexible, weak or even all of the above. To ensure a longlasting and high-performance composite part, use the right combination of cloth and just enough adhesive to keep the part together. Slopping on epoxy to wet-out a section of cloth quickly and then leaving puddles of excess adhesive adds
AMERICAN HISTORIC RACING MOTORCYCLE ASSOCIATION
NOVEMBER 2020
