I think it's a synchronous motor, it plugs straight to 110VAC and drives a fan blade.. Motor hums but doesn't turn when powered.

It has a cap rated 2uF, I replaced it still doesn't move. I replaced it again with a 4uF and can get it to move when I spin start it with my fingers. Q: Is it ok to double the cap to 4uF like that?

Also, can I oil the gap in between the rotor and the stator? I did that and seems fine as it's spinning now. But should that gap not be oiled?

 

That gap should be a gap. It never needs oil because nothing touches. Apparently, it does touch. Fix the gap.

And put the capacitor back to the size it's supposed to be.

Trying to fix a mechanical problem with electrical experiments will only result in a quick failure.

 

And put the capacitor back to the size it's supposed to be.

OK noted! But what might be somethings to watch out for in this case with the motor where I doubled the cap from 2uF to 4uF? Thanks!

 

Inappropriate current amount.

 

I think it's a synchronous motor, it plugs straight to 110VAC and drives a fan blade.. Motor hums but doesn't turn when powered.

It has a cap rated 2uF, I replaced it still doesn't move. I replaced it again with a 4uF and can get it to move when I spin start it with my fingers. Q: Is it ok to double the cap to 4uF like that?

Also, can I oil the gap in between the rotor and the stator? I did that and seems fine as it's spinning now. But should that gap not be oiled?

Post a picture if you can. If this is the style I'm thinking. The rotors should never touch on any motor. Did you check the bearings? Many use a bronze bushing. They dry out and wear, then the rotor rubs and won't start. If oiling made a difference then it's likely worn out. Check the laminations. There should signs of rubbing if I'm right. It's possible to replace the bushings if you can find a new one or salvage a good used one. Usually it's better to replace the motor.

 

Press in new bearings, or Oilite bushings.