Replacement of oil seal for Electric Balancer Shaft

[@andreyrybak5051]

Dear Collegue pls advise if this unit was installed initially or later on during ships service wnen vibration was obvious. And if main engine initially provided with counterrotating masses (counterweights). Thank you

[@mozirichiefengineer7916]

The main engine initially provided with the counterweights, and the electric balancer was installed initially.
I think the shipyard had already taken the electric balancer when designing the ship.
Thank you.