When you arrive with your motorcycle you will need the following documents:
1. A valid foreign (non-Greek) passport which will be valid for at least 6 more months from the date you arrive in Greece.
2. A valid registration from the particular "Department of Motor Vehicles" which issued the license plates for that particular motorcycle.
3. A valid International Motorcycle Driver's license. You probably can get one of these from your local AAA.
4. A valid Insurance policy. Check with your insurance broker to make sure that your insurance company will cover you while you are driving in Europe. Especially make certain that you are coverred against theft. In Greece you need liability insurance that will cover you up to $1,200,000.00.
If you have these you should have no problem. The Greek customs officials will place a stamp in the back of your passport which will indicate that you brought the bike into the country as a bonafide tourist. That stamp will allow you to use the motorcycle in Greece for up to 6 months. Before those 6 months have expired you must take that bike out of the country.
You must also have and use a helmet.
I hope this information will help you.
See also: International Driver's Licenses
Regards from sunny Athens, Tom Mazarakis