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Discussion Starter · #1 ·
New Skill attempted this winter. (Unfortunately not spelling and grammar)

My wife bought an orphaned 2000 Triumph Sprint ST this winter. The bike was parked for some time until the owner ran into and knocked it over in his garage breaking the bodywork on both sides so she decided it needed rescue.

The cost of new body parts would have totaled more than $1,200 for the 4 parts she needed so we decided to experiment with plastic welding.

This process was interesting to learn, firs you need to identify the plastic type to see if it can be re-melted on the triumph the body is ABS plastic.

Next I needed filler rod and a plastic welder; I found an air torch type welder and ordered some ABS rod from McMaster Carr.

The process is similar to complete joint penetration steel welding; first clean contaminates from the weld area you don’t want to grind in wax or silicone and imbed the contaminates into the plastic.

Next remove the paint from the area, and then use several layers of aluminum tape on the back side to stabilize the crack and hold in detached parts.

Then with a dermal tool grind a V ½ way through the material thickness also drill a small hole at the end of any cracks to stop propagation.

Next using the welding tool and filler rod melt in new ABS plastic. This takes a bunch of practice to do this accurately. I practiced on some sheets of ABS for several hours before attempting this on the bike.

After building / melting in the filler rod I used a hot iron and the air welder to flatten the weld bead to make sanding faster.

Sand the weld area flush, and then apply layers of aluminum tape to the weld joint to help pull heat away and prevent distortion when welding the backside.

Grind and repeat the welding on the backside grind to the depth just before contacting the previous front side weld.

After the backside weld is sanded flush reinforce the area with flexible epoxy and fiberglass cloth.

The finished weld area is now homogenous with the original material, this is better than repairing cracks with adhesives that are of differing hardness and only have a surface bond.

Sand the part and prep for paint.




Keith
 

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Welcome mat out

Hi and welcome to our Sprint forum Keith R:)

Thank you for a most excellent and informative first post, great photos too thanks.:)

On the being a noob here Don and i are in the habit of asking all new members to please take time to read our forum stickies to gain an idea of how we run things here.

Thanks again and enjoy the forum.

DaveM:cool:
 

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Nice write up keith, I went the epocy route to fix my fairings. It worked great for the tabs but it was to flexible for fixing cracks so I just plastic welded my stuff together. I used some of the old panels that were wrecked and cleaned the paint off. Used an old soldering iron and did it that way. Worked great and the crack is now as strong as when it was new.
 

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Good write up!

Plastic welding seems to be the best alternative for large repairs. Of course it can also be used for smaller repairs, but any of the adhesive methods will also do fine for the smaller jobs. I prefer the ABS cement for small jobs because it is not as dependent on surface prep as some of the others. But it can be a slow cure at times. On the plus side, once the solvent offgasses you are basically left with welded ABS plastic.
 

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Discussion Starter · #6 ·
haven’t tried the solvent weld

Oldndumb

I haven’t tried the solvent weld as the damage was too severe, you can see one area in the photo that is completely broken out. This is one of the recessed pockets the bolt and grommet sunk into. This area needed to be welded with multiple passes to build up the missing material. The other crack in the photo was completely though the material and ran from the part edge through a mounting hole and several inches into the part. The other three parts had similar damage.

The crack geometry did not rematch well so I thought the solvent welding would have difficulty with the gaps. I was thinking that solvent welding would be better if the crack realigned so that it was just a hair line type situation.

As for pictures of the repaired parts they will be back from the painter next week (3-12-09) ish. Basically the parts will look like a stock bike with the decal missing but I will post them anyway just for comparison.

Thanks for your suggestions.

Keith
 

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You used the best method you could have for those conditions. And you are correct, solvent welds are better with hairlines, and not as good with buildups.
 

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Discussion Starter · #8 · (Edited)
after pictures plastic welding

For those who are interested I have posted the after pictures of the parts that were repaired with plastic welding. I think the parts turned out good considering this is my first attempt.

The pictures are of the same part and same location; note the large hole in the unrepaired part that was the recessed mounting point.

Just shows that if you have time you don’t need to give up on broken bodywork

Keith
before





after



 
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