Seal Bore readings are the Rotor Centering readings with respect to the Bearing Pedestals.
It is measured by means of inside micrometers from the oil guard Seat surface to the surface of the rotor Journal. At each location it is measured at the three points, Left, Right, bottom
Seal bore readings are the reference readings for any correction and normally should not change.
But over a period of time due to change in foundation characteristics it can lead to change in seal bore readings.
1.) Ensure inside micrometers used for taking seal bore readings are calibrated.
2.) If the seal bores reading are very awkward during Dismantling, same can be improved upon during the finalization of Alignment and slope. But in the end Alignment is the Top priority.
3.) If there is no margin of improvement of seal bore then contractor should be asked to demonstrate the removal of bearing from the rotor.
4.) If the bearings come out then it is OK . But if there is problem then one has to go for pedestal rectification by offset machining for ease of bearing removal.