How to fix broken plastic bodywork (includes VIDEO)


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How to fix broken plastic bodywork (includes VIDEO)

Post by WingAdmin »



Our bikes are covered in plastic. It's great: it can be any shape, any color, it's light, relatively resilient, and (to a point) flexible.

However, it's also not tremendously strong, and a simple tip-over can cause cracks or breakage. As the bikes age, the plastic, exposed to heat (especially engine heat) can become brittle.

Replacing broken plastic can become expensive - it costs Honda a tremendous amount of money to store every plastic part, in every color, in the expectation that someone will need it - someday. That cost is reflected in the prices they charge.

Alternatively, eBay can be a good source of replacement body parts, as is our own Online Parts Store - we have tons of old bodywork on hand.

But what if the damage is not too severe? A crack is easily dealt with, but what about reconstructing a broken part?

In this article, we will be showing just such a reconstruction. We also have a video - if you want to skip to the video, just scroll down to the bottom of this article.

The broken piece in question is the right front brake rotor cover on my GL1500. There are two attachment points at the bottom of the rotor. Here is the good one:

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Here is the broken one. You can see that quite a bit of it cracked and broke away:

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We're going to be bonding to the ABS plastic. In order to do so, we first have to remove ALL paint, or in the case of the rotor cover, chrome plating. The easiest way to do this is with a small grinder in a Dremel tool:

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The chrome (or paint) on the inside needed to be removed as well.

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Now all the chrome plating has been removed:

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The tope of the piece has jagged edges that will need to be smoothed:

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This is fairly smooth, I didn't want to take too much plastic off.

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Next, we need to build up some plastic to replace what we took off (or was broken off). To do this, I use small pieces of ABS plastic. I get mine from a local injection molding factory, but you can buy a replacement ABS patch and cut it down to the size you need. It's very important to use ABS - we are going to be bonding ABS to ABS, and different plastics won't work.

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First, we start by heating the ABS with a heat gun. You want it warm enough to become soft, but NOT to where it starts to bubble or scorch.

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Start to form the soft plastic to the shape you will need. This is a trial and error process: heat, form, heat some more, form some more.

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Once the overall form is about right, I start to trim away the plastic to get it close to the shape I will need to add to fix the part.

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Trial and error again: Cut a bit, fit it, cut a bit more, fit it again.

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Lastly, once I'm sure I'm close, I will make the final cut to the piece, in this case using a cutting disc on a Dremel tool in order to get a nice, straight cut.

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The final fit:

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Now we start the bonding process. We will need ABS cement for this step. You can find this in the plumbing aisle of some hardware stores, or Amazon carries it as well. Do NOT use the combination PVC/ABS cement.

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Coat both pieces with a thin layer of ABS cement, and put the repair in place. ABS cement will actually chemically MELT the plastic pieces, so that when it cures, they become a single piece of ABS. This is why this type of repair is so far superior to other methods using glue or bonding agents. We aren't gluing pieces together, we're actually creating a new piece that is a single piece of ABS melted together.

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Next, we'll be making some ABS slurry. This is very soft ABS plastic that we can use as a paste. I start by using ABS drill shavings and cuttings.

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I put the shavings and cuttings on a piece of cardboard.

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Next, add some ABS glue to start melting the pieces together.

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MEK (available at a paint store) also works VERY well for this, and can be used to thin the slurry if it starts to thicken and cure too early.

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I start by smearing the semi-melted slurry around my repair.

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I've now coated the inside and outside of the repair in slurry, and allowed it to cure for several hours.

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Next, I take another piece of ABS, heat it up, and form it over top of the repair piece.

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Once formed, I fill it with slurry.

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Now I push the slurry-filled repair piece over my original repair.

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I repeat the process with a second piece, to give added thickness and strength to the repair.

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Lastly, I fill the outside well up with slurry as well. At this point, I leave the repair to sit and cure for several days. Normally, simple "use ABS cement to glue a patch over a crack" type repairs will cure to operational strength in a few hours. However, when you are working with slurry, it can take days before the solvent has fully evaporated and the piece has cured. Until then, the plastic will be very soft. The thinner the slurry, the longer it will take to cure.

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Once cured, I drill through the repair so the collar and screw can fit.

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I also use the Dremel tool to grind away the back of the repair, to make sure it is completely flat, so it fits snugly against the bracket to which it will fasten.

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Here is the completed repair, back on the bike. Repairs such as this normally leave the repaired part much stronger than it was originally - I don't expect I will ever have to repair this again!

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Here's our video demonstrating this repair:



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ctag
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Re: How to fix broken plastic bodywork (includes VIDEO)

Post by ctag »

Thank you for the fantastic write up, WingAdmin!

Wish I'd known about this a long time ago! I've been using JB Weld's "plastic bonder" epoxy.. It works OK, but I'm definitely going to give this ABS repair a try next time!
"Voshkie" - 1985 GL1200 Aspencade
tonycpdev@gmail.com
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Re: How to fix broken plastic bodywork (includes VIDEO)

Post by tonycpdev@gmail.com »

I have no wish to start a contradictory thread. I have read everything i can find on this topic and Wingadmin’s is the best anywhere. To say I am grateful for his knowledge, input and time, is an understatement.
I am in Australia and our retail market is very different to the USA. ABS products are not impossible to find but certainly not as common as PVC. The majority of our piping, electrical conduits and plumbing are pvc and use that wonderful blue pvc glue. I can source the composite PVC/ABS glue but as wingadmin advises, you should use ABS specific glue.
I just discovered and purchased a butane gas heatgun/solder iron. I was amazed to find it had attachments for “plastic welding” and supplied ABS welding rods. These ABS rods are fed into the ‘welding’ attachment that melts the abs into the crack. They also supply a thin wire mesh that can be melted into the bond to secure large cracks.
I literally just ordered the product. I have no experience with it.
I have an ancient ‘83 GL1100A and I have spent an obscene amount of money repairing it, not rebuilding, literally repairing. I have long cracks in the fairing inside surface and several in the pannier bags. I promise to thoroughly document the repair attempt and results but in the mean time, as the welder works purely with heat I was wondering if it will be as effective as the chemical bonding described in wingadmin’s plastic repair posts.
Knowledge is preferable but opinion is welcomed.
AaronzDad
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Joined: Thu Aug 25, 2016 1:40 pm
Location: Muskego, WI USA
Motorcycle: 1987 GL1200A Aspencade

Re: How to fix broken plastic bodywork (includes VIDEO)

Post by AaronzDad »

I posted this on your YT video and thought I'd share it here as well.

I've been doing this for years. A few things I do differently:

1) Acetone seems to work just as well or better than MEK and isn't quite as dangerous or volatile.

2) I use a small pill bottle to mix up my slurry. The bottle is HDPE plastic so it won't melt from the acetone. I can just cap it off when I'm done and if it's dried out months later when I need it again I can simply add more acetone and wait a day or two for it to all melt down.

3) I dab acetone on the edges/surfaces to be joined keeping them wet for a couple minutes to soften up the plastic allowing the chemical melding to get a little deeper. I'll sometimes soak the patch piece in acetone to get it seriously melted and slimy before sticking it onto the part needing repair. I'll fold a small piece of aluminum foil into a shallow pan to make an acetone bath and keep adding a little as it evaporates off. Naturally this has to be done in a well-ventilated area. If I can get both the patch piece and the repair part soaked enough to make them slimy like a bar of soap left in the water too long then I don't even need the ABS cement as the melted plastic is it's own cement.

4) Lego blocks are ABS and can make a fantastic structural patch/reinforcement. I used a 1x8 block (anyone familiar with Lego knows what I'm talking about) to patch the crack in the front fender next to the mounting bracket. That's a notorious problem for GL1800s with the little fender skirt attachment.

5) Window screen - fiberglass or aluminum - makes a great reinforcement layer for problem areas. This only works on small areas as it doesn't' flex or expand the same as ABS and a large piece would likely separate eventually.
AaronzDad
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Joined: Thu Aug 25, 2016 1:40 pm
Location: Muskego, WI USA
Motorcycle: 1987 GL1200A Aspencade

Re: How to fix broken plastic bodywork (includes VIDEO)

Post by AaronzDad »

tonycpdev@gmail.com wrote: Fri Feb 07, 2020 7:15 am ...
I am in Australia and our retail market is very different to the USA. ABS products are not impossible to find but certainly not as common as PVC. The majority of our piping, electrical conduits and plumbing are pvc and use that wonderful blue pvc glue. I can source the composite PVC/ABS glue but as wingadmin advises, you should use ABS specific glue.
I just discovered and purchased a butane gas heatgun/solder iron. I was amazed to find it had attachments for “plastic welding” and supplied ABS welding rods. These ABS rods are fed into the ‘welding’ attachment that melts the abs into the crack. They also supply a thin wire mesh that can be melted into the bond to secure large cracks.
...
Knowledge is preferable but opinion is welcomed.
Testing plastic to see if it's ABS is easy. Pour some acetone on a paper towel and wipe the piece in an inconspicuous spot. If it's ABS you'll get some plastic smeared on the towel. Make sure you're hitting bare plastic and not a painted surface.
Lego Blocks are ABS and work great as patches or to make the slurry.
The slurry Scott shows in his video above essentially IS ABS cement. You don't need to go buy anything special. The stuff you get in cans is ever so slightly better than the slurry but not enough to make a realistic difference. I've been using my own homemade ABS cement for years without any problems.
Your heat gun will work great as long as you have the patience for it but using acetone or MEK is much easier since you have a few seconds or minutes to get everything positioned together. The chemical process will give you a stronger bond also as it'll be deeper and more thorough.


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