|06-07-2010, 12:17 PM||#1|
Joined: Dec 2009
Repairing ABS fairings and Parts etc
Repairing and Working with ABS Plastics
Acrylonitrile butadiene styrene (ABS) is a common thermoplastic (melts when heated) used to make light, rigid, molded products.
Personally, I find ABS to be one of the easiest plastics to work with as it is easy to build small structures with. eg. I built a mini dashboard for my KLR650 which houses my Voltmeter, Ammeter, 12 Volt outlet and two blinker repeaters and is fitted just behind the windshield.
ABS is easy to mold and bond together to create a strong and easily painted structure.
Sheets of ABS (usually grey in color) can be obtained from Hobby Stores at up to 1/8th inch thick. Plastruct part #91008
If you want thicker sheets it is easy to bond layers together using Acetone as the solvent.
PS. In these days of re-cycling, manufacturers have to mark what plastic was used on the inside of the molding. This makes it much easier to identify the plastic type and how best to repair it.
In the case of the fairing on the newer KLR 650s, Kawasaki used ABS instead of the Polypropylene they used previously. Polypropylene tends to be far more durable for off-road motorcycle plastic parts.
ABS is easier to paint and to mold but cracks and shatters relatively easily which means that a fairly minor dropping of your newer KLR means an expensive replacement. Good for Kawasaki, not good for the KLRer. A new complete KLR 650 fairing costs over $500 plus fitting.
You will need:
Fine small paint brush
Small glass screw top container full of Acetone
Fine sandpaper 320 grit approx.
Small container for ABS Slurry (if required)
½ inch Scotch Tape - to close up cracks and hold pieces in place
WARNING: ACETONE IS EXTREMELY FLAMMABLE
– Keep away from flames and always work in a well ventilated area. It also removes the oils from your skin. Protect yourself appropriately.
Acetone can make a real mess of paint....that is why you work on the inside and close the gaps in the cracks.
It is important, if you drop your bike, to gather all of the pieces of broken plastic, as the broken pieces are easier to put together than trying to accurately cut new pieces to insert and to match the thickness of the original material.
So, as I mentioned earlier, Acetone is the solvent we will be using. Acetone dissolves the ABS and creates a strong bond.
Carefully piece together the broken fairing. I mean REALLY CAREFULLY !!!!
Carefully, clean all parts with a mild de-greaser. I have found DAWN washing up detergent is a great de-greaser and is cheap.
Carefully inspect the fairing and find all of the cracks.
The goal is to align the parts so that there is no gap or step where the pieces meet.
This is vitally important for a really good end result. You can use Scotch Tape to hold difficult pieces together. Generally, I repair the cracks first and then add the loose pieces into the larger repaired structure. However, always make sure that you can get the pieces to fit if you glue the cracked parts first. Once you have the parts carefully aligned, and working from the inside, carefully apply the Acetone to the inside of the crack with a fine, wooden handled brush and, miraculously by capillary action, the water thin Acetone will flow into the close fitting crack. Only apply small amounts of Acetone as a little goes a long way down a crack.
DO NOT FLOOD THE AREA YOU ARE BONDING WITH ACETONE. ALWAYS WORK WITH SMALL AMOUNTS
After 1-2 minutes the join will be handleable.
Work along all cracks until the main structure is solid.
Next add the pieces that were broken off in the same way. Carefully align each piece and bond with Acetone from behind.
Why do I suggest bonding from behind? Acetone will damage the painted surfaces if applied directly to paint. Working from behind means that any damage to the paint on the inside can easily be covered with a couple of coats of paint (flat black for example)
If you did a good job, then the only visible evidence of the damage will be hair line cracks in the surface paint.
More dramatic repairs:
If the cracks you have are not close fitting you will have to make a “Slurry” of ABS dissolved in Acetone.
To make a slurry, take tiny pieces of ABS and dissolve them into Acetone. I usually use the Polypropylene cap from a Paint “Rattle” Can which holds just enough in the inner part of the cap. Note; it takes a while to dissolve the ABS in Acetone so be patient.
Apply Scotch Tape or Electricians Tape to the underside of the open crack to stop the slurry from falling through. The resulting “Soup’ can be painted into the cracks and built up layer by layer to fill the crack. Allow at least an hour between layers to allow the acetone to evaporate away before applying the next layer.
If there are major pieces missing, you will have to buy ABS sheet from a Model Hobby Store. Sometimes they have to order it in. Alternatively, you local Display Sign Company may have some.
You will have to cut (and mold) the sheet plastic to fit in the areas where the original plastic is missing.
It really does not matter what color ABS sheet you get is as you will have to re-paint the fairing after.
You can use a little Bondo to smooth out any minor mismatch. Don’t forget to roughen the ABS surface and to degrease prior to applying the Bondo. (Always roughen and degrease to remove finger oils and mold release agents)
Kinda makes you wish you had picked up all the broken pieces..huh?
Well guys I hope that helps avoid the costly expense of replacing the fairing.
Making Custom Parts:
ABS is extremely easy to work with and using solvents is easier than heat welding.
It is great to make things like mini-dashboards and switch mounts etc.
There ya go, now you know!!
kudos screwed with this post 06-07-2010 at 12:30 PM
|06-07-2010, 06:31 PM||#4|
Joined: Jan 2009
Location: Brisbane, Australia
I've always used a gas soldering iron with hot air blower attachment for repairing cracks. You need filler rods - easiest to get from plastic repairers such as bumper repair shops, but you can improvise them by cutting up old fairings or other ABS sheets.
Kind of like metal welding - vee the join, heat the material and feed the filler rod in so it all melts together nicely. after it has cooled (a few minutes usually), grind it back with a die grinder. after that, sand and prep for painting. With decent painting, pretty easy to get seamless repairs.
I've not tried using acetone before, but will probably give it a try sometime - would be really handy for little pieces (no more burning of fingers while holding it in place!) and joining sheets for additional thickness.
Any idea on what the best solvent for chemical welding polypropylene? I have had a little success heat welding it, but it is no where near as easy as ABS, since it requires so much more heat.
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