Fairing Repair

By Richard Pass

From: Richard Pass <richard.pass@anu.edu.au>
Date: Fri, 14 May 1999 08:50:18 +1000

How I repaired a broken K100RT fairing.

Following a low speed drop on the dirt, my upper fairing was broken between the turn indicator through the lower part of the mirror mount to the edge. Because this fairing had been repaired poorly a number of times before, a chunk of the bulge below the mirror mount had broken off and disappeared when the bike went down.

Also both the upper mounting points which hold the fairing on the bracket had snapped off. The outside of the fairing showed deep cracks over these mounting points on both sides. There were a couple of deep gouges along the right side of the upper fairing. The vent of the right lower was cracked and the lower part of the right lower, just in front of the footpeg, was mangled into the crank case and cracked right through. The radiator surround had deep scratches along the right side. The mirror casing had split along the seam but was repairable. The mirror itself didn't break until I prised it out just before painting. The right pannier was gouged and scratched.

All in all, pretty sad. I got several quotes.

Adam, the guy at a local paint and shop had only resprayed the bike 3 weeks earlier and I think he took pity on me because he showed me how to fix it.

He took me to the local fibreglass supplies shop and pointed me at a kit which contained about a square meter of matting, a half a litre of resin, a little bottle of hardener, some acetone for cleanup and a wooden handled paint brush for applying the resin. I also bought some filler. All up it was around $45.00 and I still have about half the stuff left. Also get some of those disposable rubber gloves and a breathing mask which fits reasonably well. Fibreglass dust tickles the lungs, makes your hands and arms itch and definitely isn't healthy.

Preparing the Surfaces

(Put the gloves and mask on.)
The suggested repair method was to sand and remove any paint from the inside of the fairing behind the cracks/breaks and to "V" out the crack on the inside before applying an internal bandage. I noticed that several cracks on the outside of the fairing appeared to have been old cracks which had opened up on flexing. While I followed Adam's method I also decided to add some fibreglass to the outside after scraping it back so the contours would not be altered. To remove paint, glass, etc., I used 80 grit sand paper, knives, screwdrivers, chisels and whatever would do it. I'd probably have used an angle grinder if I had one.

One of the previous fibreglass bandages (in fact, the one under the major break) was not well done and came off in one piece quite easily showing that the old paint hadn't even been sanded off before the glass was applied. I removed all the dodgy previous "repairs" (about half of them) and rough-sanded each area inside and out. I removed enough glass to make room for the patches on the outside using a carpenter's rasp.

The upper bracket mounting points had been fixed on numerous occasions and were in several pieces but stuck together with what looked like chewing gum (probably filler) so I removed all that using a small screw driver like a chisel and reglued with high strength Araldite (the 3 day stuff). I used blue-tac as formwork to stop the Aradite running away. Plasticine would work. If you have lost a mounting point you can make a new one out of one of those blind nuts that hold the corner of the windshield in the fairing. (Tip courtesy of Anton Largiarder). If your fairing is badly broken you may need to insert plates and screws to hold it together "a la orthopedic surgeon". They can be removed when the glass has set. I did under the mirror mount. If you're going to fit a new mounting bracket you might want to bolt it in place as a splint.

Applying the fibreglass

(Safety gear again.)
Make sure the surface is well roughened to give the resin something to hold on to. Cut the matting to size. Allow an overlap of 1 to 1.5 inches from the edge of the break if you can. Mix the resin according to the instructions on the kit. If you do it right and the day is not too hot you'll probably have around 10 to 20 minutes before it starts to harden so don't mix too much. I found about 10 to 20 ml was right for what I was doing.

Paint a generous layer of resin on the inside in the shape of the matting. Place the matting on the wet surface and paint another coat of resin over the top. Stipple it well with the brush to remove any air. If you have a metal roller you can roll out any trapped air if the surface is flat. Allow the first layer to harden an hour or two before applying subsequent layers. On the inside you shouldn't need more than 3 layers and maybe only two. It sets strong. On the outside, to preserve the original lines so you should have removed enough of the existing surface to accommodate the repair. A little under 3/4 mm depth per layer of glass. Two layers is plenty. I mostly did one except for the spots above the bracket mounts. The glass should be cut to fit neatly inside the hole you've dug without overlap. Technique is the same as on the inside but try not to build up above the original contour. If you do you'll just have to sand it back later.


I used a high flex filler and mixed it according to the instructions on the tin. If you don't get the ratio of hardener right it will either set in 2 or 3 minutes or never set properly. Apply it with the little paddle that should come as part of the package. Or a palette knife, a piece of card or plastic. Its probably easier to apply a couple of thin layers than try to do it in one until you're practised. I spent ages trying to get the shape of the bulgy bit missing from under the mirror. I eventually mounted the mirror on the fairing and covered it with plastic food film and sculpted the filler hard up against it. Worked a treat.


Sanding is where you finally start to get convinced that this might just work. I started with a fairly coarse grade of paper (80 grit or so) to get it down to the approximate shape then 150 and then finished it with 300. As well as sanding back your repairs you should remove all the old clear gloss so the paint will stick. Deep scratches should be sanded, filled and sanded again. This worked well on the panniers as well as the various fairing scratches. Where the surface you have filled is supposed to be flat or convex use a sanding block to get the contour regular and run your fingernail gently across boundaries to check for raised edges etc. You may find numerous other cracks while sanding. Best to fix 'em now. Don't be in too much of a hurry (unless its winter, of course). Don't think the paint job will cover any blemishes. It won't and there are two tiny ones on my bike but you probably wouldn't notice them unless I pointed them out.

You may want to venture into painting but I didn't. The paint job cost me $250 and was worth every cent. The repair saved me $650 and took parts of several relaxed weekends last summer. Probably 15 hours max. I enjoyed the freedom of a K100 for a while, but its great to have an RT again now that winter's here.

Richard Pass
1984 K100RT - Bermuda Blue
Canberra, Australia

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