System cases are durable, but they can be scratched, scuffed, and are prone to fade over time. There have been several threads over the years offering various ways to deal with the cases. I bought a bike that had a Givi top case that was looking pretty rough. Feeling I had nothing to lose I decided to try to refinish the case. The results were very satisfactory.
I decided to use the same techniques on a set of BMW system side cases. I've since done an additional set of BMW system side cases and a BMW top case all with good results. While this hardly qualifies me as an expert the results were more than satisfactory for a DIY project. Here is the procedure I've been using.
I removed the lids from the cases in all instances. It made the job much easy and will result in a better final result. As you have heard before, preparation is key to a good finish, and this applies here as well. If you try to spray a coating over scratches or dry bug guts they will still be very obvious. Here is some of the damage I needed to repair prior to coating.
To deal with this part of the job I purchased Bondo Bumper Repair Kit.
This is a two part epoxy with an applicator that makes it easy to mix small amounts. It dries quickly and is easy to sand down. Prior to using the epoxy be sure the surface is clean. I washed the cases, let them dry, and then sanded the surfaces lightly with 220-320 grit wet/dry sandpaper to remove any stubborn dirt or scratches that left material above the surface. You might find a straight razor blade is useful for slicing off plastic sticking up at edges of deep scratches. The sanding also helps remove any residual film from products like Armor All or Back to Black. To fill scratches mix the epoxy in very small quantities and apply with the spreader included in the Bondo package. It dries quickly so you do not want to be trying to work on too many scratched areas with a single mixture. The double tube dispenser makes it really easy to mix small portions. After the epoxy dries sand it down with a 220 grit paper If the layer of epoxy wasn't deep enough just add additions layers as needed. I followed up the 220 with a light sanding with 500-600 grit sandpaper. Keep in mind, any imperfections in the surface will show up in the final finish.
With the scratches, scrapes, and gouges filled rinse the case/lid with running water. Mask off any areas you do not wanted coated. I wanted something durable that had the same basic look. I did not want a thick built up finish like you get with a commercial truck bed liner spray. I found Rust-oleum Truck Bed Coating to be ideal for the task.
It is easy to spray, not too thick, dries quickly, and is quite tough while still being easy to work into a good finish.
Be sure to protect areas from over spray. Following the directions on the can you will lay down a nice even coating. The product is quite forgiving so if you are too close and get a run it should just blend in on its own. If you miss a spot or are too thin just go over it with an additional spray. The coating dries quickly and will be ready for the next step in short order.
At this point the finish looks pretty nice. It is very uniform but quite rough, like 150 grit sandpaper. You might be tempted to leave it as is, but I think you'd eventually find out that the rough surface will become an issue. As an experiment I ran a high quality wet paper towel across it as you might do if you were cleaning a dirty area. As you might expect the towel shreds after a short time and now you have shredded paper to brush out of the finish.
The approach I took was to wet sand with 500-600 grit wet/dry sandpaper. You just want to knock off the sharp peaks. Some might want to stop at this point, but I found that the finish was still too rough. I followed up wet sanding with a 1000-1200 grit sandpaper.
Again, you are only taking down the roughness so use a light touch. Feel the surface as you sand until you get a uniform smoothness. I did not worry too much about a super smooth finish on the back side or the bottoms, but you do want to remove the roughness of it will attract and hold dirt. All that remains is to wash the lids and cases with running water and re-assemble.
A good thing about this procedure is that you can stop at any level of smoothness you desire. If you stop before getting to the 1000-1200 grit, and you determine it is too rough, you can always do some additional sanding later on.
Here is a before and after:
Here is a link
to additional pictures.
If you haven't sanded anything for a while keep in mind that you want to try and sand using hand pressure rather than just finger pressure for the wider areas. This will leave you with a smoother and more uniform finish and will prevent removing too much material. Another general sanding tip is to use care at all edges where it is easy to sand too much due to the small surface area.
Feel free to ask questions, comment, or add your suggestions. If you think this is beyond your skill/available time, send me a PM so I can give you some ideas on what this might cost to have it done locally.
I've placed this thread here in Oilheads because this section gets more traffic than the DIY section, and I wanted the greatest number of interested parties a chance to see it. The thread will be moved to DIY after a time. We'd like more people to become aware of the DIY section. We encourage people to contribute your own procedures. We have a wide spectrum of readers, so just because you are not an expert or as skilled as others on the board, that does not mean you don't have valuable tips and information to share in the DIY section.