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Normal Topic ABS luggage / bags repair: BMW touring cases (Read 212 times)
qwerty123
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ABS luggage / bags repair: BMW touring cases
06/04/17 at 20:09:18
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Hello everyone,

I thought I'd take a little time to relate how I repaired some BMW touring cases (old versions that use the flat latches w/ small luggage keys, as opposed to newer versions that use the tubular locks that take ignition keys). I have Krausers (and a set of BMW Krauser copies), but the touring cases are a little bigger and have much better latches. Obviously this procedure isn’t 100% optimal: please share tips, changes, and commentary! The more brains on it, the better. I took me a few hours, but I was figuring it out as I went. Hopefully it’d be faster with this procedure.

I was able to get a set of touring cases on Ebay for ~$150 shipped, and I already had the necessary racks. However, these (like many of the touring cases) had cracks radiating away from the rivets that hold on the latches—four between the two bags. At least on my cases the lids are ABS but the rest of the luggage (the piece of plastic that mounts to the rack) is something else--polyethylene? Not sure why BMW decided to mix plastics like that. One can test for ABS or not in this situation by wiping some acetone along an inside surface: if it dissolves the plastic (if you see black on the towel), then it's ABS (as my lid is). If it doesn't, it's not ABS.

ABS has the advantage of being easily solvent weld-able, and so it’s easy to repair. I’ve read about a few other methods of repairing these bags (fiberglass + epoxy, just epoxy, plastic welding), but this seemed the best to me (and I got to learn about working with ABS). One can have trouble getting epoxy to stick to plastics like ABS, though there are ways around it (e.g. rough up surface, clean with alcohol, then oxidize with a torch before gluing).

Anyway, I wanted to relate how I repaired the cracks and reinforced the cases so this hopefully won’t happen again.

You’ll require these things: 1) BMW, Krauser, etc. cases with ABS components needing repair or reinforcement, 2) Sheet ABS as here, 3) ABS cement (most any hardware store), 4) Aluminum tape or other tape, 5) heat gun or torch, 6) a variety of shaping tools (hacksaw, drill, files, block plane, etc.)

There are six main steps: 1) stop-drill the cracks, 2) Tape the cracks with aluminum HVAC tape on the outside of the case 3) prepare some gap-filling ABS cement from regular ABS cement 4) prepare your reinforcing patch, 5) fill cracks, 6) cement patches in place 7) clean up.

Procedure in next post due to character limit.
  
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qwerty123
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Re: ABS luggage / bags repair: BMW touring cases
Reply #1 - 06/04/17 at 20:31:38
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PROCEDURE:
Step 1: Drill a hole at the end of the crack to remove the stress concentration at the tip and so to prevent the crack from propagating. I used a 1/8” drill bit, and had no good reason for choosing that size. I’m sure there’s some theory about what’s best. However, it is important to drill the actual end of the crack. This was hard to see; I used a 5x jeweler’s loupe to find it, but you could use a magnifying glass or similar. If I had drilled where my unaided eye told me the crack stopped, I would’ve missed its tip and the hole would’ve been ineffective. The texture on the outside of the touring cases makes this harder than I think it would be on smooth plastic.

Why drill to stop the crack if we’re solvent welding to repair? I thought it’d be worthwhile because it’s tough to get solvent / glue into such a small and tightly closed area as the tip of said crack, and I figured better safe than sorry. It takes five minutes to do them all.

Step 2: Put some tape on the outside of the bags over the cracks. I used aluminum HVAC tape because I thought the solvents in the ABS cement might dissolve other tape. I worked it in to the texture on the outside of the case using a stippling motion with a small brass brush.

Step 3: I made some of the ABS cement a little thicker by dissolving little bits of ABS in it. This was because I wanted to use the thickened ABS cement to fill the cracks, and I thought the ABS cement might not be up to the task as it was pretty thin. Just take a small container that the ABS cement won’t dissolve (I used a shot glass), put in some ABS cement till about half full, and then add some bits of ABS. Cover and let sit to dissolve.

Step 4: Cut pieces of your ABS sheet large enough to cover the area of the cracks, overlapping by a significant amount, PLUS a bunch extra so you can fine tune as you make them. I cut the patches to both cover the areas where cracks were and the areas around all the rivets (i.e., the areas where cracks were likely to appear). You can cut your ABS with a hacksaw or by scoring with a razor and snapping along the lines.

Once you’ve got your bigger-than-necessary ABS pieces, heat them with a heat gun or torch until pliable. Wear gloves that’ll provide some protection from heat. Once pliable (quite floppy), push into the case in the area where you’d like the patch to be. Hold it there until it’s cooled some and set. If you’re trying to go over an inside corner like I was (some of the cracks had gotten to that area), you might want to cut a wedge out of the corner of your ABS patch so that you aren’t trying to form a significant compound curve into your ABS sheet. I did some with the wedge cut out and some just by forming, and cutting the wedge out made it faster and easier.

Now, use files, shears, sandpaper, etc. to shape your patches to fit as closely as possible to the plastic. ABS cement of the variety I used is found in every hardware store, but is designed for ABS pipe joints with known fit tolerances. It will fill gaps to some extent, but I thought it best to minimize them—so I cut reliefs for rivets etc. I also beveled the edges of the patch so that there was a smoother transition between the patch and the case so that stuff didn’t get stuck on the patch.

Step 5: Clean up your patch (no burrs or stuff sticking out) and the case (I used some sandpaper on the patch area followed by an acetone wipe). Spread some of your thickened ABS cement into the cracks with your gloved finger. Push it in as best you can. Remember, there’s tape on the outside of the cracks. Then, wipe off the excess from the inside.

Step 6: Cement the patches in place. Using the little absorbent swab thing on the inside of the can’s lid, spread some ABS cement around the area where the patch will go on the bag and ALSO on the patch itself. Put the patch in place and clamp as best you can. Wipe off excess ABS cement that is squeezing out as well. Let dry.

Step 7: Clean up excess cement with a razor blade, chisel, or similar. Smooth rough spots and you’re done!
  

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DeeG
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Re: ABS luggage / bags repair: BMW touring cases
Reply #2 - 06/04/17 at 23:31:16
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THANK YOU!!!!

I bought Max, a '73 R75/5 from a friend of mine who's had it since new (used to own a BMW dealership in Merced, CA many moons ago).  He can't ride on two wheels anymore, and I'm such a sentimental sucker, I couldn't see the bike go to anyone else, because he'd never see it again. lol

Still has the original Krauser bags on it, but they are cracked.  Thought that the bags weren't repairable.  yay!!

So, this thread gets printed and put in the R75/5 binder.   Smiley
  

Dee G
1978 R45/N  
1978 R80 w/hack
1971 R75 (swb)
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qwerty123
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Re: ABS luggage / bags repair: BMW touring cases
Reply #3 - 06/08/17 at 11:58:34
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I'm glad someone's found it useful DeeG.
  
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