Ally,

Even if your building is underpressure, so should the generator inside and out.  Your problem sounds like it could be the result of blocked air passages within the bearings that are meant to equalize the pressure on both sides of the bearing.  When bearings are rebuilt, it is not uncommon to have gasket material and/or poor assembly cause these passages to become cut off.

Ron Brook

Thanks for your input!

Absolutely right you've said.

Problem is solved and there was no problem with the machine bearings..

Problem was the underpressure in the building. 

Cooling air was taken from the building and blown out thru the wall.

Machine use 9000m3 of air in sec.. and airflow in to the building was not sufficient so underpressure occured. And baffle in tank was also a issue breather on "wrong"side of return oil from machine in to tank..