How to repair broken plastic

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frog357
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How to repair broken plastic

Post by frog357 »

One of the hardest things I tried to do on my spree was repair cracked plastic. Without having a plastic repair kit, or even knowing what kind of plastic this is, I tried whatever I could find in my garage.

I found a trick where you put stitches around the crack just like the doctor does when you get cut. Using a very small drill bit and 25lb fishing line, the crack is holding together good as new now. I didn't want a buldge on the side panel so I tried using other methods.
Description and Images of stitches trick


Things that work sort of:
Model Glue, it melts the plastic if you use to much so you need to use very small amounts and take your time. The problem with this is lack of strength. It bonds but it's not strong enough to witdhstand any stresses of twisting the panel. (i picked it up and turned it over and it cracked).

JBWeld, works if you make something for it to hold on to. If you try to use it on a smooth surface it'll come right off. I sanded the edges on a 45degree angle on both edges of the crack and that gave it a gap to sink into which helps make it stick. (like a V on the crack, back side of panel, keep front looking better).
This is where I got this idea (Taillight repair)


Bondo Spot Filler works good for filling scratches and for covering the stitches on the bad cracks. It works best in very small amounts, and take your time! Be sure to sand after each use, and re-clean the area before the next application.


All this being said, there must be a better solution, I know one exists, I've been told to stop waisting my time but that's all the help I got!

Ebay has panels but all I found were already cracked.


This is the stitches technique with bondo to cover, if you look close you can see a few of the stitches coming through still.
Image


This is the inside of the right panel. It was giving me a very hard time and I decided to put lots of JBWeld on it. If you wonder why I used this, it's all I had at the time!
Image


This is the outside of the right panel. I decided to use spot filler for smoothing out the high parts on the damage. So far it's looking good, I just don't know if it'll hold up for long!
Image
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Post by Spangoo »

...Dr Frankenstein. I love the way it looks with the stiches exposed. Thanks for the great tip.
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Post by Spangoo »

'stitches' - sorry
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Post by scootoe »

The back side panels are a PCABS( Poly carbonate/abutyl styrene mix) which can be melted and or fused with methel ethel keyton (MEK) from hard ware. Be careful. its toxic and could mess up the panel. A two part 5 minute epoxy on the lightly sanded back side of side panels would also work well. Bondo can be used to hide front side scratches

I believe that the kick plates and front plates( not around speedometer) are a polypropelene base plastic. This means that at a molecular level they are similar to a dense type of wax. Sometimes talc is added as a filler before parts are molded. To get bondo and adhesives to stick permanently poly propelene a primer similar to what is used in the automotive industry should be first applied. It is made by PPG or 3M and cold probably be bought at a body repair shop or auto store. You might find that bondo sticks well to it at first, but you will probably find it tends to lossen or chip after periods of vibration and panel flex.

I used to be a plastics injection molding engineer in a past life.

peace. :)
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Post by Jim »

... too many poly words :roll:
86 Honda Spree - Lawn Ornament
83 Suzuki GS450E - Sold
92 Honda CBR600 F2 - Current Daily driver
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Post by noiseguy »

The flexible plastic parts are some sort of thermoset, which means that large creases can be taken out with a heat gun and pressure if you're carefull. I used this to straighten out the knee guard and fender on mine. Heat gun and hands protected with leather gloves to smooth out the bumps.
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