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.

 

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