I havea Chessie F9 diesel loco,but dont have amtrak engine right now. My question is can i use my Chessie F9 engine for my amtrak cars until i can find a amtrak diesel engine. Gary
No. It is one of the laws enforced by the Railroad Police that this is not allowed and you can, in fact, be prosecuted for such illegal activity.
It won’t look very convincing…so try to find an Amtrak locomotive soon. There are several different models out there.
LOL
Seriously, when Amtrak started in '71, many of their locomotives and cars came from other roads–it wasn’t uncommon to see cars from say, BN…being pulled by Penn Central engines. Eventually, many of the older engines got repainted or retired when Amtrak bought new power in the '70s. With that said, a Chessie F unit wouldn’t be out of place–I don’t think Amtrak had any in Chessie colors though. If not, you could always say it’s a lease unit 
If you’re modeling in HO scale, the Bachmann Spectrum F40PH is a good locomotive, as is Athearn’s GE P42. Kato also makes an F40PH, but it’s more expensive than the Bachmann one.
You might as well, it’s your railroad, and since Chessie didn’t have any let Amtrak use it. There was never any Fs painted in Chessie colors, but it sure is a great paint scheme.