What flexible filler to use on motorcycle fairing panels?

[mangocrazy]

I've recently acquired a damaged top fairing from an Aprilia Falco, so I can modify it without feeling guilty about damaging an increasingly rare original item. The fairing has some crash damage (it slid down the track and abraded one side) . At one point it has gone through the panel, but most of the damage is surface abrasion, to a greater or lesser degree.

I'm looking for recommendations for a filler which will stick well to plastic and is genuinely flexible. Even to mount the fairing to the bike it has to be flexed over the inlet 'snorkels' that feed the airbox, so any filler will have to cater for flex. And I'd also like it to be fairly easy to sand...

Any suggestions?

 

[Kram]

First thing, what is it made of? If your lucky it will be ABS as repairs are very easy and good as new with a solvent weld filler. Use as much solid sheet abs as possible and only solvent slurry to glue it on.

Nylon can only be heat welded which is quite difficult to get right. It is easily overheated due to the narrow melting range, which turns it brittle.
Nylon can be used as a mould for ABS slurry/sheet which can then be epoxied on the back, also works on fibreglass. Epoxy can be brittle so not ideal.



Before and after. Cracks glued up and reinforced with abs, near ears added on the mirror mounts. All holes filled and redrilled for extra strength and some unused holes filled in.

 

[Ruffian]

If light scratches then fantastick is a cracking filler or there was a

Plastic repair paste made by upol and cant remember.

 

[tigdlo]

Lidl currently have a digital temperature conrolled hot air gun for £20, heat welding may not be the best route though....

 

[Kram]

Lidl currently have a digital temperature conrolled hot air gun for £20, heat welding may not be the best route though....

Nowhere near accurate enough for good results. A decent temp controlled soldering iron or modified 3d print head would be my choice for nylon.

 

[Matchless]

I used to use a tube of FPRM but don't know if it is still sold,

 

[mangocrazy]

Photographs show it more clearly than I can explain. First off, the damege on the RH side of the top fairing:

As you can see, there is surface abrasion, but one spot where the damage goes through the skin.

One of the headlamp mounts is broken and there are a few screw holes that have been enlarged and damaged and will need re-work.

There is a >PP< stencil on the inner fairing, so I presume that means the material is Polypropylene.

 

[Kram]

PP cant be solvent welded and very little sticks to it, rules out most glues. It may need a special primer when you paint it.

PP is said to be one of the easier types to hot weld. Its a common recyclable plastic so find some and do lots of testing on scrap to make sure its not brittle.
Clip lock food containers and lathe insert trays are both PP, also most plastic parts in spray equipment - gun pots, measuring cups.

It may be better to buy an unpainted ABS replacement panel, Ive found they are quite good and may save a lot of time.

 

[sg66]

First thing, what is it made of? If your lucky it will be ABS as repairs are very easy and good as new with a solvent weld filler. Use as much solid sheet abs as possible and only solvent slurry to glue it on.

Nylon can only be heat welded which is quite difficult to get right. It is easily overheated due to the narrow melting range, which turns it brittle.
Nylon can be used as a mould for ABS slurry/sheet which can then be epoxied on the back, also works on fibreglass. Epoxy can be brittle so not ideal.
View attachment 327044
View attachment 327045

Before and after. Cracks glued up and reinforced with abs, near ears added on the mirror mounts. All holes filled and redrilled for extra strength and some unused holes filled in.View attachment 327048

Where do you get said filler and slurry from?

Cheers

 

[mangocrazy]

PP cant be solvent welded and very little sticks to it, rules out most glues. It may need a special primer when you paint it.

PP is said to be one of the easier types to hot weld. Its a common recyclable plastic so find some and do lots of testing on scrap to make sure its not brittle.
Clip lock food containers and lathe insert trays are both PP, also most plastic parts in spray equipment - gun pots, measuring cups.

It may be better to buy an unpainted ABS replacement panel, Ive found they are quite good and may save a lot of time.

The only part I'll be hot welding is the headlight mount. Everything else will be filled. Which is why I asked for recommendations for flexible filler that can be used on plastic - PP in this case,

 

[Kram]

I dont think fillers will adequately stick for the amount of flex you need, except for hot welding to build it up then sanding back to shape.

However google suggests these

Home - U-Pol

U-POL is a World leader in automotive refinishing products specializing in fillers, coatings, aerosols, adhesives and paint related products.

www.u-pol.com

Novol Professional Repair Kit for Car BUMPER Trim FIX Filler 500g Putty Plastic : Amazon.co.uk: Automotive

Novol Professional Repair Kit for Car BUMPER Trim FIX Filler 500g Putty Plastic : Amazon.co.uk: Automotive

www.amazon.co.uk

Where do you get said filler and slurry from?

Cheers

Use a sealable small glass jar/pot and add your choice of acetone or MEK solvent, add scrap ABS until consistency is like mixed epoxy.

 

[sg66]

Could bond a thin skin of aluminium to the rear to give it strength, I've done that in the past with thin plastics.

 

[ajlelectronics]

Instinctively, I would be using glass mat and epoxy resin behind the hole to brace it and then fill from the front with more mat and epoxy resin, before skimming with Dolphin Glaze. West systems make some kits for the repair of specific plastics And they seem to be the experts in that field.

The rest of it needs a coat of epoxy primer or two before skimming, again with Dolphin glaze. Get West's advice though for your specific application.

 

[optima21]

this is the stuff that I'm using on plastic model kits. I was originally using milliput epoxy putty, but that kept cracking and falling off as it was too rigid.

I was worried what it might have come up with when I googled "big boy filler"

in the past I've used Plastic Padding Elastic filler on plastic car bumbers, it was fine until some crashed into the car

 

[mangocrazy]

Thanks for all the suggestions/tips. Rather than replying individually I'll try and cover it all in one post.

1. Replacement panels are simply no longer available. A good copy would have been my preference, but they are also non-existent. It's for that reason that I refuse to cut up my OE panel and looked for one that I could cut about without feeling too guilty. I need to modify the top fairing to accommodate higher bars which in turn are needed for my ageing bones.

2. The section that has the hole is problematic, as immediately behind that (and in very close contact) is a snorkel leading to the airbox. If I add extra material inside the fairing that will push it out of line and put all the fairing and screen mounting holes out of position on that side. So I need to find a way of sealing that hole without encroaching into the internal space.

3. Before posting I did a search on Ebay looking for flexible plastic filler and there appear to be a number of options. Most of them claim they are formulated for bike fairings and car bumpers, but I always prefer a personal recommendation rather than just manufacturer's claims. One that did get my attention was Upol Plast X 6 'highly flexible body filler for plastics'. Upol are a major player in the paint/filler game so I'd hope it would do what it says on the tin.

https://www.u-pol.com/uk/en-uk/prod...st-x-highly-flexible-body-filler-for-plastics

 

[Morrisman]

Upol is the only filler I’ve used for years and years, it sticks like the proverbial to a blanket, and is flexible. I’ve used it on both metal and glass fibre and never had a problem.

Just removing it from the plastic filler spreader I use requires a sharp chisel, once it’s set. Flexing the plastic doesn’t work.

 

[the snooper]

I would plastic weld anything that needs is, from there give it a bit of a flat to remove any fluffy bits of plastic, from there a coat plastic primer followed by some epoxy primer, then filler, most is quite flexible when used quite thin shape it another coat of epoxy and ready to paint

 

[ajlelectronics]

I would plastic weld anything that needs is, from there give it a bit of a flat to remove any fluffy bits of plastic, from there a coat plastic primer followed by some epoxy primer, then filler, most is quite flexible when used quite thin shape it another coat of epoxy and ready to paint

If you use a plastic primer, there is no point using an epoxy primer as the surface has already been compromised. One or the other, preferably epoxy primer.

 

[ajlelectronics]

2. The section that has the hole is problematic, as immediately behind that (and in very close contact) is a snorkel leading to the airbox. If I add extra material inside the fairing that will push it out of line and put all the fairing and screen mounting holes out of position on that side. So I need to find a way of sealing that hole without encroaching into the internal space.

Once repaired, you can flat the repair patch on the inside. It is there for stabilising the repair whilst it goes off.

 

[the snooper]

If you use a plastic primer, there is no point using an epoxy primer as the surface has already been compromised. One or the other, preferably epoxy primer.

But plastic primer is there to promote adhesion between the plastic and other paints, the epoxy on top gives you a base to fill on with less chance of going back through the plastic primer