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Integral Bag Repair

Integral Bag Repair

By Jonathan Jefferies
March 1995

Mike Clark asked about Repairing BMW Side cases:

Can any president out there offer a suggestion for gluing a broken segment of a BMW side case? I have a half dollar size hole and matching section (approx the size of a 50p coin for those in the U.K.) of one of my side cases that needs to be glued together. This is on the black plastic cases that go with a ’93 K75S (cases manufactured in ’92).

The case appears to be made with ABS plastic (sez “ABS” on the inside.) I tried ABS solvent weld cement, the kind used for ABS pipes and fittings, but it was inadequate.

Ah, yes the side cases. We need a super FAQ about these. I assume you mean the saddle bags, aka side cases, aka hard bags as opposed to the side panels that are actually on the bike. I have found by experimentation that there are possibly two different plastics or two variants of the same plastic. I have had some luck with the outer case using PVC/ABS glue. The inner case – the part that hangs onto the bike – does not respond well and it’s usually the piece that breaks. Anyway it can be plastic welded. This requires the use of a soldering iron with a flat tip – available from Wellar Industries. The professional versions have a temperature control rheostat. And requires the use of plastic welding rod from the Urethane company, 1-800-633-3047 There are 7 different types of plastic rod/stock and costs range from $14-$24 /30 feet of rod.

Now that said, unless you’re a confirmed “do-it-yourself” person, that you go to the local bike shops and ask for someone who can do plastic welding and pay $25 or so to have a skilled person do it. But this is an art form and you need to scout around to find an “artiste” type.

Jonathan Jefferies (jeff@Mri.com)


By Tracy DesLaurier
September 1995

Regarding plastic welding/repairs to your bike parts:

K-bike bags are made from two different types of plastic – the inner sides High Density Polyethylene (HDPE), and the outers Acrylonitrile Butadiene Styrene (ABS). Don’t try to repair them using the same materials. HDPE needs to be welded by using a device similar to a hair dryer, but it provides a much hotter and more directed source of heat. The heat gun may force air through it while warming up or cooling down, but it is imperative that the air supply be switched to nitrogen before attempting the weld or it will not stick properly.

The ABS side can be repaired using a “bodied solvent”, but this type of repair is probably suitable only for very small holes, or to reinforce an area with another piece of ABS stuck to its backside. ABS can also be hot air welded, and nitrogen is not absolutely required, but better results are achieved by using it.

Three years ago I had a bag fall off on me and repaired it myself using these techniques at my dad’s plastic business. The bag is holding up 100%. BTW, for repairs to fairings, do not use these techniques, as they are primarily fibreglass. Use conventional fibreglass repair techniques, but substitute epoxy resin for polyester resin on major repairs.


Super Glue and Baking Soda … and Repairing Plastic Saddlebags

From: Jeff Dunkle <dunklej@bellatlantic.net>
Date: Fri, 14 Jan 2000 04:53:10 -0500

Robert S. Atkinson wrote, in part, to a thread I started:

> The application is correct. The baking soda is ‘filler'(?) & the load
> is light for airplane models.
> Is there belief that the baking soda shortens the cure time? This
> is the part I’m interested in!

I asked Paul Burns from the Classic Wings Club list if I could repost a piece he wrote there. He said…..

Sure thing… (I hope the Beemer folks are as pleasant as the CWC people.) The only caveat that I have is that this was written based on my knowledge of the GL1000 — I can’t say for sure what materials BMW has used where.Best regards,
Paul Burns

(here’s a copy of what he wrote to that list – based on some professional background)
If anyone is interested, there is a reason that the superglues work well with the side cover repairs: The covers are molded out of ABS (Acrylonitrile-Butadiene-Styrene polymer or plastic). Most of the superglues on the market are methacrylates of one kind or another, and are particularly good at bonding to the acrylonitrile. Someone mentioned earlier about using baking soda in conjunction with Crazy Glue. The baking soda is a base (as in acid-base) material that causes the methacrylate to “kick” or cure quickly. As a rule, it isn’t a recommended practice for the material as, if it cures too quickly, the bond that develops isn’t as strong as when you let it cure more slowly. Also, be careful of using methacrylate glues around polycarbonate (like helmets, visors, etc.) as many of them can cause crazing and cracking of the polycarbonate (not too good for appearance and absolutely a time bomb for strength of the polycarbonate).

The folks who are advocating welding using a soldering iron — that is probably about as good a structural bond as you’re going to get. If those of you who are so inclined can get your hands on some ABS sheet (check with spa, plastic fabrication, or sign shops in your area — they will sometimes let you get between the workbench and the trash can, if you know what I mean), and have the patience for it, you can make a welding tool suitable for the job out of a piece of 1/4″ or thicker bar stock — stainless is best, but cold roll steel will work. The method you are going to perform is called hot plate welding. You need to put a decent polish on it (400 grit or finer emery paper). Get a piece that is as wide as the tab and long enough that you can clamp one end in a vise and still have at least five or six inches sticking out like a blade itself. Next, heat the bar until it is hot with a torch or heat gun. If you have a way of measuring its temperature, you want to heat it to around 350 to 400 F. (If you don’t have a way of measuring it, put a drop of water on top of the bar; heat until it boils off. Keep heating until water dropped on the bar “dances” or skids around or off like a ball. For the culinarily inclined, kinda like the temperature you want a skillet at when you are going to fix pancakes.) Remove your heat source and push the pieces to be bonded from opposite sides of the bar until their surfaces soften — probably less than 15 seconds. If it takes much longer than 15 seconds, the bar was probably too cold. Be careful not to heat the cover portion so much that it causes the outside to move or deform. When the parts are good and soft, pull them away from the bar and press them together, making sure the parts are properly aligned with each other. Now, hold that pose. After a while, the plastic will harden and, voila — the welded assembly.

Whew. This may have been more than any of you really wanted to know! Hopefully those interested enough to make it this far might like to know where all that came from — in my misspent youth I attended University and obtained a degree in Plastics Engineering, of all things. I knew it might come in handy someday! ;-P (<— tongue firmly in cheek!)

Paul Burns
Lake Elsinore, CA
Senior Member, Society of Plastics Engineers
Big Blue, ’78 GL1000, Dressed

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