One of the side cases I got with my motorcycle has some fairly significant cracks, and the previous owner's shitty repairs were shitty and didn't work. I don't want to spend $500 on a replacement set of bags, and replacement parts are no longer available.

This piece is stamped with PP-TX20 which seems to mean that it's Polypropylene with some talc mixed in.

What would be the best way of repairing this for it to be reasonably strong and not look too too ugly?

Plastic welder, filler material of same plastic type, and screen door mesh cut to shape (melt the metal mesh inside the plastic bridging the crack for strength).
Add plastic and sand back to shape.
Finish will look fucky. Paint can help.

>>2923354
So far so good, I'll just have to see if it holds up.

>>2923923
Nice, anon. Some type of rubberized coating like flex seal or an automotive undercarriage coating would probably even it out and make it look not bad.

>>2923923
a soldering iron works well for this. can be done without mesh or filler if needed you just use it to melt and move material to where its needed and then you work it into the surroundings. obviously not all plastic is melt and formable like this.

>>2923923
neat

Another update, the bottom crack is fully taken care of, I'm only able to pick away at this when I have a few minutes here and there.

Initially I was going to just leave the crack on the outside and only do my repairs on the inside, but I figured I might as well try it out on this area that's not visible when they bags are installed on the bike, it's... Okay. I've read about adhesion promoting primers that can work with polypropylene that will actually allow bondo to properly stick to the surface, so I may try that out if i need to make the top side a little ugly.

>>2924809
Here's a before of the outside

>>2923923
BONDO
O
N
D
O

:^)

Started into the second crack, have it tacked in place for the moment, still needs more filler and smoothing - I've been using window mesh and then steel wool on top of it, but the crack is closed up and stable now, which will let me get into the real tight spots

Nice work OP. Are the repairs holding? Motorbikes shake a lot so I'm curious.

>>2926345
I haven't fully re-assembled everything yet, but I'm pretty well done the plastic welding bit, there was an additional crack I had to fix up, and a screw hole I needed to rebuild, but that's all done and it feels really solid though.

I also riveted in a piece of aluminum to reinforce the bottom mounting holes that join the inner shell to the outer shell and hinge.

here's another view of the repaired crack. I'm probably gonna get some plastic polish or something to try and smooth it out a little more.

You can also see the screw hole and tab that I needed to rebuild here, don't have a good pic of that yet.

>>2926679
From the other side - you can see that one of the plastic holes had ripped out, and two others were stretched and almost ready to break, I'll probably throw a tiny bit of paint on these so they don't stick out as much.

here's the rebuilt tab and screw hole.

Turns out tim Hortons ice cap cups are actually polypropylene, and as such, are compatible for use as a filler material.

Using a hot air gun, a soldering iron, and a putty knife I was able to melt down a large cup and knead it enough to become a solid, void free lump of plastic, about twice the size of what I needed. I also added in some steel wool to the molten plastic to kind of turn it into a composite, along with some of the black filler rod for colour, once it was fully kneaded I was able to get it hot and smush it down into a reasonably flat piece which I then cut and sanded to approximately the right shape, and then I welded it in using the same window screen, soldering iron and plastic filler rods method as I used for the cracks. It feels quite solid now, and I can knock it down with a file as needed if the latch for the case down quite go.

All done

I used some plastic polish to get the repaired area on the top to about the same lustre

>>2927703
Looks good! There's too much shit broken on my bike that I don't have the motivation to fix it.

>>2923346 (OP)
Heat gun set to a proper temperature and a PP welding rod. Before welding, make a groove with a mini grinder (use low RPM!), at least 1/2 of material thickness deep. Use your heat gun to melt the welding rod and put it into the groove to create a seam. Set the temperature just enough for the rod to push a wave of plastic melt forward. Wait a few minutes for the seam to cool down. Remove the extra plastic from the seam and polish it with the grinder.

NEVER use soldering iron. NEVER use steel wool, wire, etc. NEVER use glue. Neither of that will last.