6101154130. I use many of these each month. If you are testing the motor with a battery, use one with about 5 volts left in it. Many guys hit the motor with a 9 volt motor and insist the motor is good. At 9 volts, you can sometimes get a bad motor to spin a bit. Today, Lionel uses this as the primary motor that fits just about everything. The same goes for the reservoir/fan chamber. That motor and reservoir/fan chamber is used in the high end locomotives and LionChief Plus. I am a fan of this set up. No longer do we have to be concerned with the resistor hitting the side of the chamber and shorting out. Even at retail pricing, the smoke fan motor is very cheap. You are going to pay shipping so you should throw in one or two extras to have on hand. Being the Lionel Tech for Charles Ro, we order them in batches of 25 often. This is a good post as it reminded me to get an order in as I am down under 10 on hand.
FWIW, to get a stock Lionel smoke unit to smoke it's best, throw away the fiberglass pad and use the eight inch rope style wicking (reaganized) part number 691SMKP008. If you have to replace the resistor, seat it down a bit lower in the bowl to push the wicking down. This is so the incoming air from the fan motor does not get blocked in any way by wicking sitting high in the chamber. . You want to get all the air flow you can get to push the smoke skyward.
If you are a fan of a big smoke show, contact GRJ and he can get you hooked up with equipment to get the job done.