I have purchased a sewing machine motor from aliexpress. The issue is that it spins in the wrong direction. I opened it and only see 2 wires going to the brushes.
Electronic – Reverse universal motor from a sewing machine
acmotor
Related Solutions
Your motor is 'timed' to operate in one direction by advancing the brushes. This is clearly visible in picture #2, where the brushes look to be rotated anticlockwise by about 12ยบ relative to the stator.
Advanced timing increases rpm in one direction, but reduces it in the other direction. A motor that is 'neutral' timed will go the same speed in both directions.
The timing on your motor does not appear to be adjustable. You could try removing the brush holders and springs from the board and drilling new holes for them, but it may not be worth the effort.
It looks like Charles' point that you can't get to the windings is the case. There looks to be three wires coming from the windings and no starter switch. so you have this case:
So it looks like the white/orange is tied to the two windings, main and aux, (the lower line). So unless you can reach into the windings and reverse one of those, you can't reverse it. If you can, you want to bring another wire out so you can separate the connection from main and aux. from the white/orange.
Best Answer
Summary:
Disconnect the wires from the two brushes.
Reconnect the wires to the brushes that they were not connected to before.
(A little extra wire will probably be required).
Done.
Universal motors are what is known as "series wound" - they have the whole motor current flowing in series in both the field coils and the armature.
When the AC supply reverses the current flow to both field and armature also reverse so the same relative polarity is maintained.
To reverse the motor direction you thus either need to swap the wires to either the brushes or to the field (but not to both). eg
Wire previously going to brush A now goes to brush B.
Wire previously going to brush B now goes to brush A.
There is a chance that the motor is designed mechanically to work better one way than the other but if there is no prospect in using the motor as supplied reversal may still be acceptable.
As @BrianDrummond notes -
Brushes optimised in position for one direction of rotation may be slightly off position in reverse.
As @Charles Cowie notes -
This is electrically the same as swapping brush leads but may be easier. It's unlikely to be possible in the present case (based on the photo).