I have a belt drive whole house fan. I replaced the entire unit after a motor failure. I wish to take my old fan and fit with a new motor and use the fan for other purposes. I have tried an washing machine motor, a drill press motor and other types. All quickly fail or turn off due to overload/thermal protection I think. What type of motor do I need for this application?

30 inch fan with pulley and belt. I am even re doing pullies to turn it much slower and can't find motor to run it. I know nothing about motors.

On the motor there should be a nameplate that has can tell you the motor type, horsepower and needed voltage

Also, if you know the manufacturer of the fan, you might be able to track backwards and find the parts list for this fan motor.

You could "match" the motor that came out of the old unit if you still have it or call the manufacturer. Electric motors have ratings much like a car motor does. In horsepower. Also they have optimal rpm's. There should be a sticker or plate on the motor with the specifications on it.

Sounds like either the motors you are trying aren't powerful enough to operate the fan blade, although a washing machine motor is fairly sturdy. Can you freely turn the fan blades with your hand, and when you stop turning it does it keep turning? If the blade doesn't free wheel, that could be part of your sizing problem.