Where are the vin numbers on the motor?

It can be in a variety of places, depending on the make and model of the vehicle (i'm assuming that you are inquiring about the engine VIN on a car).

Access and viability might be very difficult on a new car, as the older cars were made with more room in the engine bay (they also had less stuff in there).

Engine VIN numbers are usually stamped on the crankcase (the bottom portion of the engine). It will usually be placed in an area that has been flatted during the casting process (the manufacturing of the component), so that they have a nice surface to stamp on to. It can be any number of places: under or over the exhaust manifold, on the intake side, on top, in the front,.. with a rag (for wiping off grease, a flashlight, and patience, you'll find it.