When 85 or 86 is energized, the circuit between 87 and 30 close so power flows through.
So power is now passing through 86 to 85, but 85 is wired to the second relay 87a, which is the closed circuit supplying power to 30 for the other side of the motor.
87a is closed when no power is applied to 85 or 86. Now you have back flowing power into the second relay preventing your motor from turning because it is getting power to the motor in both directions.
