You can over grease a motor bearing which can cause damage eventually to the motor especially if it's an electric motor being over greased.
If you over grease an electric motor it can cause the electric motor to overheat and cause bearing failures and even damage to the electric motor windings, especially if the excess grease comes into contact with the electric motor windings.
Over greasing the electric motor bearings allows grease to be forced out of the bearing seals and into areas that it shouldn't be in like the windings which can affect the electric motor's insulation and performance and could cause the electric motor to start smoking when it's in operation and could even potentially catch fire.
Electric motor grease is often blue in color although some electric motor grease may be red or have a milky white translucent appearance to it.
Electric motor bearings should be greased every 3 months to every 6 months or sooner if the electric motor sees a lot of use or heavy use.
When greasing an electric motor you grease the electric motor using the grease ports and a grease gun where the grease is injected into the grease ports which are located on the ends of the motor where the shaft or shafts extend out of the motor.
The grease then greases the bearings that the electric motor shaft spins on.
The best grease for electric motors is a grease that is synthetic GIV, PAO base oil grease with an NLGI 2 or 3 consistency is often the best lubricant for electric motors that require grease.
For electric motors that take oil for lubrication often 3 in 1 motor oil or SAE 20 motor oil is the best lubricants for most electric motors.
When oiling an electric motor you put between 2 to 4 drops of oil into the electric motor for each bearing, depending on the size of the electric motor.
Generally you can just put the oil into the electric motor a drop or two at a time until the oil reaches the top of the oil port.
Avoid over oiling the electric motor though as it can cause damage.
Electric motors require oil if the electric motor has oil ports which are located on each end of the motor housing where the motor shaft exits the motor.
Some electric motors have sealed bearings and don't require any oil and if there's no oil ports or grease ports the electric motor does not need any oil or grease.
But if the electric motor does have oil ports or grease ports they need oil or grease to keep the bearings lubricated.