Will running the Semi-Scale O-27 Hudson N 4-6-4 without smoke fluid cause any damage to engine?
If it is meant for smoke fluid, you can burn out the smoke unit's heating element.
To replace will be around $40.00.
There might be a switch to turn off the smoke unit, look on the bottom of the steam engine, otherwise you can open the engine(remove the top from the engine with about four screws) and remove the wiring harness from the circuit board and that will quit sending power to the smoke unit.
Lee F.