How to fix crack in CX500 plastic rear fender?

[Krisby]

Allo, I've just noticed a crack in the plastic rear fender of my CX500, where it mounts to the frame.  There are two holes for the securing bolts, and one has an obvious crack, and the other hole is just starting to develop a crack.  Any ideas how to remedy these fractures?  It would help if I knew exactly what kind of plastic these fenders are made from, so that I can search for some compatible glue.  Has this ever happened to anyone else?  Please see photos below:
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[CX PHREAK]

If you can find a source for the parent material {spare fender liner etc.} this stuff can be welded with a soldering iron.

i have modified one for a bike I'm currently building this way.
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[82 Turbo & 2000 Valkyrie]

see this link - how I did my blinker lens

https://www.australiancx.asn.au/forum/index.php?topic=12363.msg154332#msg154332

it's not really difficult and if you want to strengthen the area - just get some similar material from an old fender and weld it in place

[Mins Man]

I haven't got a clue what type of plastic they are, but I found cable ties worked pretty good for repairing the dash pieces on my turbo.

[CX PHREAK]

There's cable ties and there's cable ties. I guess not all are the same plastic. But this is where I started with the guard above and it didn't work for me. The bond was weak and the material inflexible after trying to bond it.

 I ended up cutting strips of the parent material with an angle grinder to use as filler rods.

 

[Joolstacho]

I believe the only way to do a PERMANENT repair on a job like this is to laminate both sides with a wide strip of Epoxy resin impregnated glasscloth.
Plastic welding is a temp solution at best, it'll always fail at the edge of the weld if there's any tension or vibration.

[CX PHREAK]

Maybe .... but I actually did try to tear the fender liner above apart.

[Krisby]

Hmm, plastic welding seems the way to go, as long as the appropriate filler material can be sourced.  From what I've seen online, preparation of the surface is important, and not unlike that of metal welding.  If the crack is sufficiently "V"ed, and the plastic rod filler is of the right stuff, then the strength of the repair should be as good as was the original condition.

Joolstacho:  When you mention "Epoxy Resin", is that the same as "Styrene",  which is the resin usually used with fibre-glass cloth?  If so, will it really bond with the subject plastic fender (assuming the surface is roughed up in preparation)?  I believe Styrene is also used in plastic body filler compounds.

Well, it looks like I'll have to do some experimentation...............

[CX PHREAK]

Polyester is generally used for fibreglassing {it may also be called styrene, I don't know} Alternatively epoxy can be used. It is stronger but more expensive.

 Polyester generally won't bond to waxy plastics like the fender liner but epoxy may.

 But I've always found welding with the parent material best.

[Joolstacho]

No, forget Polyester resin if you want good adhesion. Epoxy resin is the only way to go. And roughing up surface prep is all-important.
Ships Chandlers often stock West Systems Epoxy resin, that's the stuff.

[VC3]

Why not just buy a good used inner fender and be done with it?


ps - make sure you have the fender plate, #9 in this schematic:

https://www.partzilla.com/catalog/honda/motorcycle/1978/cx500-a/rear-fender-i

[DR CUSTOMS]

Hi all,
There are different types of plastic used for fenders by OEM manufacturers.
The 'hard' type is usually ABS (Acrylonitrile Butadiene Styrene) widely used for motorbike side covers, some fenders and farings. Not the modern dirt bikr 'flexible' fenders.
The best repair method is to use an ABS liquid (better than epoxy, fiberglass, etc. - i've tried them all) as it is an identical compound to the parent material to be repaired.
ABS sheets are available on ebay for $8. Acetone dissolves the ABS to a liquid - ratio 1:4. Break ABS into small pieces. Place in a jar with acetone for 1 hour.
Sand the parent plastic with 400 grit. Apply ABS liquid. Add plaster mesh tape for reinforcement. Allow 24-48 hours to cure.
Perfect bond, no delamination, very cost effective, paintable.
Cheers
DR CUSTOMS

[jhovel]

The inner guards are not ABS. I suspect they are polypropylene. If that's the case, no resin - epoxy or otherwise- will make a permanent repair. Plastic welding - done properly - is the only realistic option. Scraping the oxydised edges and cleaning with acetone of the work AND the filler immediately before the job is essential. It is best done  with hot air rather than a soldering iron because the oxides from the iron will recontaminate the weld. That's why they crack again later on....
Chemical welding as I do a lot with ABS is not possible with propylenes.

Cheers,

Joe