Hi guys,
I have a 1990 BMW K100 LT. Some time ago, I was outside the 10 cm high asphalt line , was not able to recover, and the bike very slowly turned over in the ditch.
I had almost come to a complete stop, however, the weight of the bike made the lower side panel crack into two large and one small piece. 

Could someone tell me me what they are made of? Is it polyester and glassfiber, or epoxy/glassfiber? If it is the first, then I should repair it with polyester, epoxy will not stick for long. I also plan to add carbon fiber on the backside of the panels, to strengthen them. Here too, it is important to know if it is polyester or epoxy that have been used.

BR, Sigurd

standard fibreglass epoxy resin and fibreglass matting seems to work well ...but make sure there is a lot of overlap

the fairing material is like a powdered form of fibreglass , so whilst strong there is no lateral strength ...which is a real pain

ive done quite a few fixes using fiberglass



good luck

Hi Charlie, thanks a lot for your speedy reply.
Sigurd

Hi Sigurd, +1 to what Charlie says. I too have had a visit to the scenery wrecking the same panel on my LT . I used fiberglass kit to repair it too. 

Instead of heavy glass mat I use 3 layers of surfacing tissue to get a good strong ply effect. Be sure to sand off the paint and rough up the repair area well for grip of the epoxy and overlap as Charlie says. Once you have the panel back together working on the inside you can use epoxy body fillers on the outside after dremeling out the cracks.

Here's a pic of the Repair to My K1100rs windscreen surround done the same way:

good advice Will

All that frizzy stuff at the break is perfect for reattaching the broken bit.  I just push the parts together interlinking the strands.  After carefully aligning the parts I liberally apply thin CA glue followed by a catalyst.  This will hold the parts in alignment while I make the rest of the repairs.

The panels are made of bulk molding compound(BMC) which is also used in other familiar items like the agitator in a washing machine.  Polyester resin is the best choice because it not only is very compatible with the BMC, but it cures much faster than epoxy which helps avoid resin runs and sags as well as creeping mat as it cures.  With polyester a complete repair can be done in a couple hours where with epoxy it will take a couple days.

For the reinforcement, I use several layers of 3/4 oz cloth which is sold to model makers in hobby shops.  It is very easy to work with, it saturates easily and molds to the surface shape readily.  It is thin enough that a layer or two can be applied to the outside of the repaired part after grinding the surface down a bit.

For filling in cracks after using a Dremel(or a sharpened beer can opener) to open them, I use a product called DuraGlas which is a polyester filler reinforced with glass fiber.  It has a greater resistance to cracking than regular filler so that for minor cracks no fiberglass is required on the outside.

The process to follow to make repairs to the panels is outlined in Chapter 4 of West System Epoxy's Fiberglass Boat Repair & Maintenance.

OK, call me stupid but, why isn't anyone just 3D printing these things??

I spent £50 on a couple of side panels for my 1979 Suzuki GSX750 (there were none to repair) hate to think what I would have to cough up for genuine BMW ones  but in my head I can't see why someone hasn't set themselves up in a little workshop somewhere just making whatever is needed! 

I'm sure there is a reason but......

I've repaired a fair amount of K Tupperware using a fiberglass repair kit from the auto parts store.  Works fine.

Prior to applying the fiberglass, I rough the area up with sand paper or a Dremel and then clean that with rubbing alcohol so that the fiberglass resin has a good clean surface to adhere to.

Here's a smashed up K75 belly pan that I repaired using fiberglass:

I used to do fiberglass repairs in a boatyard.  When I started, we used the West System, but gradually went back to polyester because the working properties were better with polyester.  Epoxy simply cures too slowly and flows too much requiring strategies to keep things in place while the stuff cures.  Epoxy also develops a blush as it cures that must be removed before secondary operations are done like paint or further reconstruction.  In my experience, the only thing the West System has to offer is the ease of getting the correct ratio through the calibrated pumps and the fillers for specific functions. 

The only place I have used epoxy in fairing repair is to reattach mounts.  For this I use a good 5 minute epoxy in two stages.  First to attach the mount, and then a second stage where I build a fillet around the break with epoxy mixed with a quantity of very short chopped glass strands cut from a 2 oz cloth.  All the surfaces the fillet touches are roughed thoroughly with 80 grit paper and cleaned with alcohol and left to dry for 10 minutes minimum.  I try to make my fillets at least 1cm and larger to spread the load as much as possible.  Even with 5 minute epoxy the fillets are a pain to make.

The information in the West technical bulletins is good, but applies primarily to stressed hull and deck structures.  There is little stress in the parts I have so far had to repair on my fairings.  As such, a lot of the West technique is overkill.