Repairing cracks in fairings? | Page 2 | GTAMotorcycle.com

Repairing cracks in fairings?

GreyGhost said:
Think about the surface area inside the crack. That's why people grind it out, you can triple your effective area to give the adhesive a chance. If you don't grind it out, you could build it up, but a)doing that on the outside would look terrible and b) the crack will still exist behind and serve as a stress riser to crack your patch.
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So best to do it from the inside then?
 
MaksTO said:
Is that photo just the acetone/plastic combo on the back? I was thinking either exhaust tape inside, epoxy outside, or maybe this can work too. Just not sure what the proportion of plastic to acetone should be? I would assume until its just a goop of sorts?

I also see it's common to dremel out the crack sometimes on the outside for filler, but I hope that with the acetone solution that might not be needed? Just maybe sanding the outside before touching up the paint if I do so.
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yes the white and black stuff you see that is gooped on is the slurry, add enough acetone to melt the ABS/Lego and make it almost a paste consistency

here is the front view, with some bondo work and primer

1985 YAMAHA FZ750 Rebuild Project

and the finished part now painted

1985 YAMAHA FZ750 Rebuild Project

.
 
Every plastic weld attempt I ever seen on a trials bike fender failed quickly, stitches pull the damaged parts together, that's why they work.
So if you weld it and it breaks again there, just stitch it together with about a 20 cents worth of zip ties.
 
Here's how I do fairing crack repairs, stitch and glue method:

1) Prepare the crack. Clean the back side using acetone then sand approx 1/2" on each side of the crack. Find the end of the crack then drill a 1/6" hole from the outside of the fairing though the crack. This is to stop the crack from running any further.
2) Mix ABS slurry (as noted above). 30ml acetone to same quantity of ABS. I like using lego because you can get close to the base plastic colot of the fairing. Black ABS looks a bit rough when applied. The slurry should be the consistency of white glue. If it ends up too thick: add acetone and mix. Too thin: leave the container open, stir every few minutes -- the acetone will evaporate and the slurry will thicken.
3) Spread the crack using the blade of a knife, press the slutty into the crack and the drilled hole from the back side of the fairing. I use a latex gloved finger to push it into the crack. Remove the knife, clean up excess from the finished side then hold the plastic in alignment for a few minutes. Let the ABS dry.
4) Stitch: Prepare stainless steel T5 staples by separating and trimming tangs to approx 1/16" (ling enough to bit into the plastic, short enough to not poke thru. Using forceps and a soldering iron, heat the staple legs until they be pressed into the back side of the fairing.
5) Build up a patch 1" wide and a 1/6" thick on the back side using the remaining abs slurry.

I've repaired lots of fairings this way, some that were blown to pieces. If the finish side isn't too scraped up you can get away without paint.
 
Trials said:
Every plastic weld attempt I ever seen on a trials bike fender failed quickly, stitches pull the damaged parts together, that's why they work.
So if you weld it and it breaks again there, just stitch it together with about a 20 cents worth of zip ties.
Click to expand...

Street bikes don't go through the same stresses as your trials bikes , so typically the slurry will hold up for a long time, usually the part breaks in a whole different area, and not where the repair was done.

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... and possibly the fairing is way better supported with brackets, but if it does break there again, the stitches will work.
 
Mad Mike said:
Here's how I do fairing crack repairs, stitch and glue method:

1) Prepare the crack. Clean the back side using acetone then sand approx 1/2" on each side of the crack. Find the end of the crack then drill a 1/6" hole from the outside of the fairing though the crack. This is to stop the crack from running any further.
2) Mix ABS slurry (as noted above). 30ml acetone to same quantity of ABS. I like using lego because you can get close to the base plastic colot of the fairing. Black ABS looks a bit rough when applied. The slurry should be the consistency of white glue. If it ends up too thick: add acetone and mix. Too thin: leave the container open, stir every few minutes -- the acetone will evaporate and the slurry will thicken.
3) Spread the crack using the blade of a knife, press the slutty into the crack and the drilled hole from the back side of the fairing. I use a latex gloved finger to push it into the crack. Remove the knife, clean up excess from the finished side then hold the plastic in alignment for a few minutes. Let the ABS dry.
4) Stitch: Prepare stainless steel T5 staples by separating and trimming tangs to approx 1/16" (ling enough to bit into the plastic, short enough to not poke thru. Using forceps and a soldering iron, heat the staple legs until they be pressed into the back side of the fairing.
5) Build up a patch 1" wide and a 1/6" thick on the back side using the remaining abs slurry.

I've repaired lots of fairings this way, some that were blown to pieces. If the finish side isn't too scraped up you can get away without paint.
Click to expand...
Sounds like about a days project. definitely like the sound of this method. Thanks for being so thorough.

So just to be clear I will need:
- Acetone
- White lego (for my white fairings)
- Knife
- Drill + 1/6" bit
- T5 Staples / cutters / pliers
- Soldering iron or some other heating mechanism
- Sand paper
- Latex gloves

That list was more for myself than anyone else. This sounds like a fun rainy day activity haha.
 
One thing I am curious about regarding cleaning with acetone and sanding - I assume there's a risk of the acetone melting a bunch of the plastic off if I don't wipe if off quickly after?
 
Or do an ugly repair, grind it off smooth and cover it with 3M shrink wrap. <- helps hold your repair together too ;)
 
MaksTO said:
One thing I am curious about regarding cleaning with acetone and sanding - I assume there's a risk of the acetone melting a bunch of the plastic off if I don't wipe if off quickly after?
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it won't eat it up that fast......LOL

melting the Lego will take a better part of a half hour, give or take....
 
I had a similar problem when I may or may not have drifted my car into a snowbank a few years back. Good suggestions here albeit a bit complex. This worked for me (and has survived a few more snowbank collisions)

Pull damaged parts off
Sand backside for better adhesion
Find something for a backer – I used somewhat flexible ABS sheeting
2 part quickset epoxy on each part
Stickem together and align the crack.

I guess it would depend on how the part broke. In my case I think it was cold enough out that the plastic broke pretty cleanly and the paint stayed in place. Once it was aligned you couldn’t tell it ever happened. YMMV
 
r3r3r3 said:
I had a similar problem when I may or may not have drifted my car into a snowbank a few years back. Good suggestions here albeit a bit complex. This worked for me (and has survived a few more snowbank collisions)

Pull damaged parts off
Sand backside for better adhesion
Find something for a backer – I used somewhat flexible ABS sheeting
2 part quickset epoxy on each part
Stickem together and align the crack.

I guess it would depend on how the part broke. In my case I think it was cold enough out that the plastic broke pretty cleanly and the paint stayed in place. Once it was aligned you couldn’t tell it ever happened. YMMV
Click to expand...
If I feel lazy this sounds like a good option too. Though its on the top of the fairing so very curved. Might be hard to attach a piece of plastic to that unless its very thin.

Seems like I am off to the lego store sometime in the near future.
 
I usually drill a tiny hole at the end of the crack to keep it spreading and then plastic weld with a scrap faring bits or other ABS material.
 
I use super glue from the hobby store , along with backing soda as filler/ harder.
Cyanoacrylates harden almost instantly when dripped on baking soda. Put a tiny amount of baking soda in the crack and drip on the glue from the back. Then backup the repair with a little bit of fiberglass cloth. Fill the weave with the soda and drip on the glue. Watch out for the puff of vapor when it sets, it can sting the eyes a bit.. I have been using this method for about 30 years . You want the thinnest glue you can buy , not the thick or the jell ones.
 
I like the crazy glue idea except that it is water soluble.
 
Trials , are you sure ? People used to use it to apply fg cloth to paddles and to seal up wounds .
It hardens into acrylic plastic , a rando quote below ..

Cyanoacrylate glue is actually an acrylic resin, not a traditional adhesive in the mold of water-based school glues. Some crafters or automotive repairmen may be familiar with other acrylic resins such as bondo, the clear liquid used to embed small objects. Usually an acrylic resin consists of two separate liquids, one for pouring into the mold and another used sparingly as a hardener. In the case of this type of glue, the hardener is water.
The main ingredient in super glue is called cyanoacrylate. If glue made form cyanoacrylate is placed on a perfectly dry surface or certain plastics, the chemical cannot form a bond with the surface. But if there is even the slightest amount of water present, including moisture from the air, the molecules of the glue have a chemical reaction and form into tight chains between the two surfaces being bonded. This reaction happens within seconds of the water and cyanoacrylate making contact. Traditional white glues rely on evaporation to form their bonds, but cyanoacrylate glue generates its own heat for faster curing.

I have never had an issue
 
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