Painting your motorbike is easy if you are prepared.
Most painters will tell you that preperation is the key!
If your erecting a 4 story building and your slab isn't straight, it only gets worse the more levels you put on. This is very true for painting, think of each layer of paint as a level in a building, if your bottom level's got dings in the paint so will the top level.
Preperation is what somebody does to the existing paint so that it will accept the new layer of paint without too much disruption. I've found in my experience that paint loves to react to new coats, and bubbles start forming, which can be fun for a 12 year old boy, but its not something you want appearing.
You want a primed surface that's clean of dust and grease (grease is paint's enemy)
Sanding is used in order to remove layers of the current paint.
If you are giving your bike a new coat of paint, its recommended that you do the following:
If you are removing dings you probably would do something like:
No doubt the first time you attempt to rub back and bog up some dings you'll find yourself going through the process a few times.. This is normal
A good way of checking if your surface is ready for painting, is to run water slowly over it, water will ripple over parts that are uneven or jagged.
Once you have finished sanding back your part, its always important to use a good Primer so that the topcoat will stick to the plastic.
Usually its ok to just go to your hardware store and pick up a can of some primer, Grey is the most popular colour, but you will find that the primer can, and does, affect the colour of your top-coat. So its usually a good idea to visit your local paint Colour Matching guy and find out what base coat to use.
Priming parts that are partly sanded, ie. have some exposed bare plastic, means you ''may'' get reactions from the current paint vs the primer.
When a reaction occurs, you get unsightly bumps in the paint, which if not dealt with will make your paint job look shocking!
In my experience the best way to solve reactions like this is to prime very lightly, letting the reaction occur, then re-coating the primer a little more, sanding back a little bit, recoating etc etc...
Slowly building up the primer, whilst letting the primer fill small inconsistencies that exist due to the reaction.