Repairing plastic body work.

I've repaired any number of motorcycle side covers and fairings over the years up until now I always had to settle for an epoxy or glue that only did a fair job of adhering to the plastic. Not even JB Weld will actually ahere to ABS. The best you can hope for is a mechanical connection where you roughed up the surface you're trying to repair. I know there are epoxies that claim to be able to repair plastic. To test their effectiveness I use denatured alcohol to clean the surface of the plastic and then without roughing up the surface I apply a drop or a dab of whatever product I'm testing and let it cure. So far, I've found no epoxies that will actually bond to the plastic.

Currently I'm repairing a chopped down fairing for my 85 1300. It has several large stress fractures that I think are caused by flexing. I could see that the PO had applied some sort epoxy filler in futile attempt to reinforce the cracks. His effort failed when the epoxy filler split at the same locations. I used a wood chisel to split most of the thicker sections of his epoxy off of the plastic and cleaned the area with alcohol. In the past at this point I has usually resorted to fiberglass fabric and JB Weld, which probably would have sufficed this time except that this effort was going to consume way more JB Weld than I had ever used before. I knew that whatever I tried would have to incorporate some sort of fiber reinforcement. I also knew that the plastic was ABS. It took a while but I finally realized that there was no reason why I couldn't use fiberglass fabric for the reinforcement and black ABS pipe cement for the adhesive/resin. It worked great!

Yep. The largest single mistake in plastics repair made by shadetrees is thinking that any adhesive-based process is going to match the elastic properties of the original piece. ABS, polystyrene, polypropylyne, polyethylyne, PVC, etc., all have different elastic properties inherent to the material and merely attempting to glue them together is essentially re-creating the original weak link.

There are "welding" processes available for the different types, and a kit is available from:

motorcyclecity.com/tools/welders.htm

...that pretty much operates like a hot melt glue gun.

While that's the best adhesive solution, it still doesn't adress why a particular part failed in a particular place - and that's stresses placed upon weak spots due to contours, materials, or both.

While fiberglass re-inforcements work pretty well, they still suffer from differing adhesion and flex absorbtion properties from the original material, often winding up in a separation failure near or at the original point.

The best patching process I'm aware of is to reinforce the area with a patch whose thickness is determined by the need for flexibility or stiffness, welded as a backing plate to the original.

Complex-contour patches - like side cover edges - can be made by making a cast of the original piece with quick-set concrete, then taking a piece of the patch material and gently heating it with a propane torch and forming it to the contour.

Like Pterosaur mentioned, I like the plastic welders. AFAIC, they're the "bees knees" when it comes to solid plastic repairs.

It's amazing how well the welds hold, and with the proper prep work and a good repainting are almost not even noticeable (at least from the outside).

I had the badly damaged fairing on the GPz I once owned plastic welded and repainted (with NOS decals) at the Kaw dealership I used to work at, and at less than half the cost of buying new!
The only noticeable sign that it had been repaired was the thin black lines (the color of plastic "welding rod" used) on the inside of the fairing.


Plastic welding kits are listed on eBay all the time, ranging from about $40 ( WELDER WELDING KIT FAIRING PLASTIC PVC ABS 50 Sticks ) up to about $150 ( MINI-WELD AIRLESS PLASTIC WELDER 5500HT AUTO/MOTORCYCLE Best Known/Most Popular Professional Weld Kit! w/VIDEO! ) depending on the quality of the kit and what's included with it.

Here's what I use at work an ABS and other plastic parts. 3M makes a product foe repairing plastics that comes in a tube that may be easer to use. The Duramix uses a gun to push the material out. You can get either from an automotive paint store.
Mark

Post edited by: Mark Wing, at: 2006/06/03 22:29

Sorry Guys,
I had to sign off earlier before I was able to resize the pics.

I like this system because it maintains the flexibility of the base material.

Bill

The forum software doesn't seem to like my pics. I'll put em up myself and link to them.

Post edited by: KZCSI, at: 2006/06/03 19:15

Maybe this time.

Here's the crack before I went after it.



Here it is with the fabric bedded into the glue.



And with a topping coat worked into the fabric.



Here's the inside surface.





The glue cured up smooth and hard in about an hour.

Bill

Mark Wing wrote:

Here's what I use at work an ABS and other plastic parts. 3M makes a product foe repairing plastics that comes in a tube that may be easer to use. The Duramix uses a gun to push the material out. You can get either from an automotive paint store.
Mark<br><br>Post edited by: Mark Wing, at: 2006/06/03 22:29

Sorry here's the stuff

This 1000 tail was missing most of the mounting areas. I used part of a Saturn car outer door for the plastic and the underside isn't that pretty but it's strong. I use a plastic mesh as a bridge sort of like the mesh dry wall tape.
Mark

Post edited by: Mark Wing, at: 2006/06/03 23:37

Here's how it looked after I painted it, never know it was in pertty bad shape to start with.
Mark

if it is ABS you can use PVC/ABS cement that you get at the hardware store in the plumbing area, you can also mix some shavings off a abs plastic and make a putty to fill in gaps,