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Discussion Starter #1
Over in my TR7RV restoration diary I mentioned that I was trying to restore the plastic air filter covers.

I bought this:

I've used the ali and chrome versions of this with mops on my bench grinder very successfully, but not had much success with the plastic.

They are the '73 on covers, so without the flutes, just a plain surface. I can buy repro covers cheaply enough, but I would like to get the originals back to be near the quality of the powder coated side panels.

The covers are fine structurally, no cracks or significant gouges. They do seem to have a streaky pale grey 'stain' to them - which I think is oxidation. The plastic polishing kit does work to a point in that it will produce a shine, but there's still the grey streaky marking to get rid of.

I suspect I need to sand back (wet and dry) the covers to a clean plastic, with say 380 and then 800 grit, before trying polishing again.

I did give them a good sanding with 800 grit, then thoroughly cleaned with acetone before trying plastic paint. Useless. the paint rapidly crept away from numerous points to leave a surface reminiscent of the surface of the moon. I suspect, that no matter how much I clean them, there are very small point sources of oil accumulated in tiny pores over many years. Painting isn't going to work.

Anyone done this before and if so did you get a good finish? Given the amount of work involved, I may be better off cutting my losses and buying new, but I would like to keep the originals if I can. Any ideas?
 

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Hi Andy, Do they still fit tightly around the alloy housings? Air leaks, gaps around edges is a serious problem with these. They tend to warp in many ways & areas.

Hard to tell how deep the grey goes. Fine wet/dry used wet can help. Finally buffing to shine like you think. Depending on black you painted tin covers it may never match. different shades of black. I find Kylon Gloss black is a good match.

You could try painting covers also. Specific gloss black for plastic paints are made. Call some auto body supply shops if needed.
Sadly there was a rumor floating around some years ago about aftermarket alloy smooth covers. I could never find a listing. I doubt they ever existed.
Don
 

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Discussion Starter #3
Hi Don, I've tried painting but I think there's so much very small spot oil contamination It's not going to work. Polishing is my only option, unless someone knows different. I just need to work out how to get that polished finish with the kit I've got.

They do seem to fit well, and they are fairly undamaged, no cracks, splits, bits missing or gouges. If I could make them look something like I'll re-use them. I'll accept they'll never match the new glossy black powder coat on the metal side panels, but hey, this is a rider not a no-oil-or-pistons museum piece.
 

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What about finding some alloy covers and either having them powdercoated to match, or if possible, sand/machine off the flutes or even fill if the flutes are lower/deeper than the base?
You could use the fluted ones and mask off the fluting as a contrast?
 

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I had the same problem. I ended up sanding them down to the plastic, using JB Weld to fill any pitted places, priming them and then shooting a coat of base coat and clear coat on them. Then I buffed them out and they look like new.
 

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Acetone as a panel wipe probably was not the best idea. If you want to paint them you will need to use an adhesion promoter before applying a filler primer.

Rod
 

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Discussion Starter #8
Hi Redmoggy, I used a Rustoleum paint product, for direct to plastic, no primer required. I'm convinced the paint didn't apply well because there's muck in the moulding that I can't shift.

I have just tried polishing the seat catch knob, with some success. I used the finest of the 3 waxes I bought, and the finest mop, and that seemed to work - hadn't previously tried these 2 parts of the kit. Got quite a good finish, much better than when I used the other 2 waxes (coarser) and their mops. I think the filter covers will polish up, I just need to work out how to do it.
 

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I would be inclined to think that your issue was the acetone. Acetone is an aggressive solvent that will remove most paint finishes, it will also attack plastics. My guess would be some of that acetone got a good bite into the your freshly sanded surface and remained long enough to react with your paint. I've done a few plastic and GRP covers and they really only require scrub with hot soapy water. Use of an actual panel wipe solvent will remove oil left over from skin, waxes etc.

Rod
 

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Discussion Starter #10
Hi Rod,

That's interesting. I'll try again and this time use some panel wipes, or some cellulose thinners maybe - I have plenty of that.

I've plenty of isopropyl alcohol too - that seems to be the ingredient of panel wipes.

Many thx for the tip.
 

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I painted my plastic side covers once with Krylon for plastic , matte black or flat black. It adhered well and I’ve never had to refinish them. paint is probably 5 years old.
 

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A friend of mine has shown me pictures of motorcycle parts that he has cleaned with his soda blaster and there were a lot of plastic items. The results were really good. There were all kinds of plastic parts, even old plastic oil tanks from jap bikes that came out really nice.
 

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Hello Andy, Just read thorough your restoration, beautiful build! As for the plastic side covers, I have done quite a bit of restoring of plastic fenders, tail lights, turn signals, and side covers. It takes a lot of time to do them right. Can’t say the discoloration of your side cover will be removed with this process.

Fill a bucket with tepid, soapy water, turn on some music, and start with the least course sandpaper you think will remove the heaviest scratches, then dip the part and sand in one direction. Keep both the sandpaper and part wet and clean, use lots of water. The part will now look awful. Use the next finer grit and sand 90 degrees from you previous sanding until you can see that all of the previous scratches are gone. On some parts I have had to start with 220, but normally start with 360, 400 or 600. I will normally go through this process and finish off this stage with 2500 or 3000.

Then on the buffing wheel with a loosely stitched buffing pad and a rouge for plastic, carefully buff the part. Soft pieces like fenders and side covers can melt while buffing. Yes, I have done that and had to start over. If you do your lenses, care must be taken so any part numbers, etc don’t get sanded.

If done well, you parts will look like they did new in the 1970s. If not, then back to the plastic paint.

Good luck and enjoy your beautiful bike!
 

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Discussion Starter #16
Thx to all and especially jpj for taking the time to respond. I've realised that I'll have to really flat them down with wet and dry and then just lightly polish. I've had a play with a very soft buffing wheel and the finest wax that I could buy, and that did make a difference, but getting a good finish on the two panels is not a quick job. But, I'll have a go. Fortunately they are not scratched, just generally scruffy.

If I really screw it up, or just can't' get a reasonable finish, I'll have to buy new parts- they are at least available.
 

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Discussion Starter #18
Apologies - I solved the problem but forgot to post on this thread.

Painted them and they look good. A friend suggested that the bullseyes I was getting was because the plastic was insufficiently keyed, so I spent some time with 400 grit wet and dry getting them well keyed. Then several thin coats of the plastic paint primer, followed by a rub down with wet and dry 1000 grit, then several coats of top coat. I am very pleased with the result but will give them a couple more coats in a few weeks. I can do better but am waiting for the paint to fully cure before a final flatting. The pic is before I fitted the blanking plugs in the covers where the twin carb intake would be.

The paint was Rustoleum Direct to Plastic and the matching primer.

Thx to all for all the help and advice.


20200205_174417.jpg
 

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The only success I have with painting metal or plastic is using base coat clear coat applications. I sand down to the plastic, apply a primer coat and then apply the bae coat clear coat. Works great for me.
 
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