HOW TO: Plastic weld and paint prep

So you have a cracked plastic fairing on your bike. Most people trash it and buy a new piece.

Not anymore, you can fix it yourself easy. Here's the how to on how to plastic weld ABS plastic fairings. I start out with CBR 1000rr tail I fixed and continue the how to with the custom work I did to make an undertail.

Whether you're fixing a crack or doing custom work like me, the process is the same.

All four major bike brands: Kawasaki, Yamaha, Suzuki, and Honda all use ABS plastic Fairings on their sport bikes. ABS is weldable, and very easy to work with when heated with a heat gun, not all plastics are. You can buy extra ABS on Ebay for cheap for fixing holes or customizing. 

-Matt Behning
(Stillwater MN)

 Plastic Welding is not hard. Especially on forgiving ABS. Start with a bargan fairing off the internet like this. Just $40.

 First step is to cut into the cracked plastic to cleary expose what needs to be welded. No need to cut all the way through just enough to make a valley on both sides.

 Here's the inside of the same crack. Be sure to grind the "V" cut into the plastic past the crack to be sure the split won't keep spreading after the fix.

 Sand off the paint to help cut down contaminants. 

 All you need is a cheap soldering iron, I use these 30 watt irons. Also donor plastic of the same type to fill.

 Welding two ABS plastic parts together is possible. I bought theis 1/8" thick sheet on ebay, formed it with a heat gun and cut it to fit my 1000rr tail.

 Start out by melting both sides a couple mm

 Push the element all the way through to insure the weld is making it through all the way.

 It will creat a depression and bulge out on the other side.

 Melt off a small chunk of ABS to fill the depression 

 The chunk of ABS needs to be completely melted to prevent a "cold weld" (a false weld caused by not heating the plastics together well enough... it'll crack clean apart with little effort otherwise.

 A cold weld is nearly impossible to see until you start sanding after welding... even then it's hard

 I made this one to show;)

 Here's the cold weld from the other side.

 I went over the top of the weld to make sure the weld was fixed all the way

 Weld small sections at a time. I heat and melt up both sides through and then add extra plastic to the weld.

 After the slurry of the weld is complete you can level out the puddle by passing back and forth.

 If you weld good enough the back will only need to be leveled out with the soldering iron.

 Here's the finished weld with the soldering iron alone. Next step is to sand with a sanding block and 80grit.

 You can use a typical palm sanding block like this bondo one or a piece of wood works.

 Here's some sanding done with 80grit cuts a lot down without gouging too much. Change directions often and never sand in circles.

 Sanding in this direction with 80 grit will form the curvature. Get it perfect because once painted every ripple and lump will show.

 Here;s some sanding with 220 since deep sanding with 80 was done.

 Here's the piece ready for thin work with bondo then filler primer, etc. 

check out the follow up posts on how to pain your motorcycle fairings you welded.

-Matt Behning
Stillwater MN