Don't know how well this will work with scratches. But in the process of restoring this 1990 Orange/Red K75S I wanted to clean up the windscreen. Not that it's useless but it definitely is not really meant to be looked thru. While at the paint store I spotted these little kits for cleaning/clearing up sun faded plastic headlight covers. As they were only $5.00 I decided to give it a try. The kit consists of two gloves, 1 pc of 3000 grit wet/dry sand paper(about 1/2 of what I would call a regular sheet) and two packets of a creamy substance. So I wet sanded both sides of the windscreen. It is a relatively small screen. Then I toweled it mostly dry and let it finish air drying. This is covered in the instruction sheet. Then I opened one of the creamy material packets, actually a folded wet towel with material impregnated in it and using the edge of the wet towel covered both sides of the windscreen with overlap between brushings. Waited 10-15 minutes and then used the other packet to do it again. After drying completely I found that the yellowing had been largely removed and I was able to see through it. Would not recommend this for a windscreen you need to be able to look through. But for one which you can look over and if you prefer a clear screen as opposed to painting it, I thought it did a reasonable job. Now I found this in the US but would expect something similar to be available anywhere.

J.

I have a K75S windscreen that a previous owner painted black. Looks fine and is low maintenance.

That looks really nice. I did the same with my K75C with the T windscreen. But I've been experimenting with painting and decided to see if I could restore the windscreen as well. Finding that orange/red color was a major issue. For what I paid I probably should have changed the color but it was only the fender and then the tail piece which had some major scratches. Anyway, after paying more for the paint than I did for the bike   thought $5.00 for the windscreen. Biggest issue is just cleaning the bike after it hasn't been touched since 2008.

duck wrote:I have a K75S windscreen that a previous owner painted black. Looks fine and is low maintenance.

Question, is the paint applied on the inside or the outside of the windscreen?

Both. It's a really good paint job so I suspect he had it done at a paint shop. I don't think it's rattle can.

It's very easy to clean. Since it's paint I just use cleaner wax on it.

I'm reminded of the small "flyscreens" once commonly fitted to racing bikes in olden times.
They were literally made with insect mesh.
Racers would "get down to it" with their chins on pads on the fuel tanks (now you know).
They could be seen through, and hardly ever cracked or got foggy.

Another way to clear up yellowed windscreens (or plastic car headlights) is to slice in half that large orange you've left in the fridge for too long. Pour a good shake of baking soda onto the fleshy part of the orange. Grasp the half-round orange in your palm and with a circular motion firmly wipe the citrus and bicarb against the plastic, occasionally wetting the surface with clean water. Rinse and repeat. One orange will do both sides of the 'screen and it will come up clear and scratch-free. If left outdoors or used heavily, after three or four months' time you'll have to repeat the process as UV rays will return the originally clear lens to yellow. No harmful chemicals are used which if left to run down the road into the gutter and further on to harm the little fishies that are afterall just trying to swim to clean water where they'd like to lay their eggs.

Autosol followed by toothpaste. I'm serious.

Dai wrote:Autosol followed by toothpaste. I'm serious.

Yeah, but seriously the cheapest autosol is USD $19. Think the kit I picked up at $5. is a better deal.
But while we're one the subject of metal polishes, how does autosol work out as an aluminum polish? And does anyone have any comments on various ways to clean/polish the engine?

About the windscreen, the description (but not the title) makes me think that it might be a polycarb screen, rather than acrylic. 

I've used "Jiffy" a kitchen cleaning product cause it's cheaper than toothpaste, for acrylic, but that won't work for polycarb, it will only make scratches.

You can remove scratches from polycarb with a butane torch. Adjusting for a sharp blue flame with no yellow flame held about three inches away from the screen in a circular motion. You have to look at the screen at an angle where you can see a reflection. As soon as it gets a gloss, move the torch to a different area. You want some scrap pieces for some practice tests. Also for practice, hold the flame about four inches from the screen, then move in slowly to get a feel for it.

daveyson wrote:About the windscreen, the description (but not the title) makes me think that it might be a polycarb screen, rather than acrylic.

So we don't know which BMW uses, Acrylic or polycarb? Just guessing but suspect polycarb as well. Is there a practical test to see which it is?

Can we trust AI?

• Colour: Polycarbonate has a blue edge because a bluing agent is used in its production. Acrylic is clear, but high-quality acrylic can have a soft, mixed colour. Recycled acrylic can look slightly yellow.
  
  
• Polishing: Acrylic can be polished to a high shine, but polycarbonate cannot.
  
  
• Flexibility: Polycarbonate is more flexible than acrylic and can be molded to fit. Acrylic is stiffer and more likely to crack when shaped or drilled.
  
  
• Impact resistance: Polycarbonate is more impact resistant than acrylic.
  
  
• Heat resistance: Polycarbonate can withstand temperatures of up to 240°F, while acrylic can only handle up to 190°F.
  
  
• Chemical resistance: Polycarbonate is resistant to chemicals like gasoline and acids, while acrylic is not. 
  
  

Yep, I'm impressed with that description, and with AI, I'm going to get AI installed on my phone soon.

If you have one scratch on acrylic, you can polish it out with jiff or something like that. If you try that on polycarb you end up with thousands of scratches, so only try a small area if you're not sure. 

Bend a strip of acrylic over a bench, it will get to say 30 degrees, then snap. Polycarb you can bend 180 degrees so that the two ends touch, it won't snap, just bend, twist or distort. Therefore it's much safer if you crash. If you try hard you can get it to break, but it won't be with a snap. Some say it won't even crack if hit with a bullet.

Great work AI. But is there a simple test that you can apply to an existing product without destroying it? I'm still guessing that the windscreens are polycarbonate. Just because they don't feel like the acrylic plastic I've played with in the past.

Acrylic is less likely to scratch compared to glass and other plastics such as polycarbonate. And any scuffs that mark its appearance may be able to be polished out. 

Acrylic is known to age without pronounced discoloration, such as yellowing, compared to other plastics.*

*Google Gods

Two Wheels Better wrote:Acrylic is less likely to scratch compared to glass and other plastics such as polycarbonate. And any scuffs that mark its appearance may be able to be polished out. 
Acrylic is known to age without pronounced discoloration, such as yellowing, compared to other plastics.*

TWB, I couldn't agree more:

The canopies of all Ecos were made of acrylics.
Mine was built in 1997, the canopy has some minor scratches (me bad) but no discoloration at all after all these years.
The scratches can be polished out, it just needs quite some TLC.
I got myself some polishing liquid recommended by Peraves(R).
I do have to rely on NW's aka Mr. Peraves' vast knowledge and experience of three decades.
The price tag is considerable as he took the best of the best by default.

jjefferies wrote:But while we're one the subject of metal polishes, how does autosol work out as an aluminum polish? And does anyone have any comments on various ways to clean/polish the engine?

My armchair wisdom because I'm sat in the house and can't be assd to do a full check Most of the engine is cast so you're not going to be able to really polish it. For that, some form of spray-on ally cleaner will help lift the dirt. The cam cover is the only exception and that can be either machine or hand polished. Autosol is okay for hand polishing but don't ever use it over the top of something that has been machine polished as you will simply dull the machine finish.

I have a bench-mounted polisher and while the results can be really spectacular, you've really got to want to get there because (depending on the metal) there are multiple polishing steps and hours between start and finish. With ally, apart from the end result looking really pretty, it has the unexpected benefit of slowing down corrosion because the surface prevents oxide from getting an easy grip.

If an engine is split down for a ground-up restoration, I will always advocate for vapour blasting. It not only cleans the surface but seals it as well and the slurry is fine enough to easily wash out of the oilways. I have an empty set of Guzzi engine cases that were vapour-blasted fifteen or more years ago and they look like they were done last week. Similarly, I have a Guzzi engine, gearbox and bevel drive that were vapour blasted ten or so years back, built up and then put into storage. They look like they were cleaned yesterday.

Thanks, I wondered about vapour blasting, now I know.

I know that the k100 and K1100 screens I restored had some sort of a hardened coating on them (as evidenced by gaps where old stickers had been removed). The coating is much tougher than you'd expect. I cut them back with 1000 grit wet paper, then 1200, 1500, 2000 and 3000 followed by Farecla G3 cutting compound and finished them off with a coating of Maguiars PlastPX polish which I topped up every few months. The results were very acceptable.

jjefferies wrote: But is there a simple test that you can apply to an existing product without destroying it? 

Two wheels better mentioned some differences. 

One way would be to try polishing a small inconspicuous area, like on the side facing the fairing between the mounting holes. If that results in scratches, it wouldn't be noticeable, but if you really wanted to, you could bring it back to glossy with a butane torch.

Many years ago I sent a sun faded screen off a K75 over to the UK to the late MikeP and he cleaned it up using toothpaste and then polished with a product called Autoglym super resin.

He posted a photo of it partly done so we could see the difference. MikeP seemed to be a very patient man in his high quality restorations so it may have been a slow job.

Anyway if interested it can be seen at the following thread, post numbers 122-124.

https://www.k100-forum.com/t6604p100-will-i-never-learn

Cheers

Gaz wrote:Many years ago I sent a sun faded screen off a K75 over to the UK to the late MikeP and he cleaned it up using toothpaste and then polished with a product called Autoglym super resin.

It's still available - Autoglym do a large range of different polishes.

I'm going to guess that the windscreen coating is an anti scratch polyurethane clear coat similar if not identical to the clear coat applied to factory paint jobs.  If anything it is harder because it's not intended to be repairable like a paint finish.

Polyurethane is amazingly tough stuff as anyone who has had to deal with removing polyurethane industrial adhesives will attest.