We are often asked to repair plastic petrol tanks and motorcycle windscreens. In the case of the former we say no even though we have in the past repaired one. We only did it as an experiment to see if it could be done and the customer had spare tank material we could use to plug the holes. Did it work? As far as we know; we tested it with water in the workshop with no leak but petrol is another matter. We are happy to try another as a test to see if it works or not. BUT the material has to be identical to the tank you want repaired.
As for motorcycle windscreens we can repair them as long as they are made from Polycarbonate and the crack or piece broken off can not be seen when repaired. There is nowhere to hide with clear materials as you can see from the picture. Once repaired and prepared the plastic go’s a milky colour. Imagine how that would look running down the middle of your screen.
On a more serious note, in some cases broken screens are less expensive to replace than have repaired.