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Spindle Motor Sealed Bearing Grease


Feb 19, 2019
I'm replacing the spindle motor bearings on my mill. I removed the motor from the machine, removed the pulley and spacer, and removed the lower bell housing from the motor. It looks like the grease over time ran out of the bearing, and there's lots of it in the bell housing. It almost looks like there's more grease in the bell housing than there could have been in the bearing to begin with.

The replacement bearings are sealed and thus pre-lubricated. They're also the bearings speced in the Mitsubishi manual, so they're getting replaced with the factory recommended bearings.

My question is should I clean out all the grease that's at the bottom of the bell housing? Should the new bearing go in clean and dry? Or should there be grease in the bell housing between the bearing and the wavy washer?

Pictures here: Spindle Motor Bearings - Google Photos

I realized there's no good picture showing how much grease is in the bell housing. I'm going to go out and take a picture of that and add it to the album in a few minutes.
Sealed bearings need no extra lubrication. However your photos show shielded bearings which are not the same. The shields are not leak tight and only meant to prevent dirt ingress.
I am not sure what is the factory recommendation, but with shielded brings I like to pack some grease in front of the bearing.
Yes, you're right, they're double shielded, not sealed. The bearing on that side is a
NTN 6408ZZC3 and on the other side
NTN 6310ZZC3

So I'm guessing I should clean that old grease out and put fresh stuff between the bearing and the housing? Any particular grease I should use?
If you're using sealed bearings, the only reason to use additional grease is for corrosion protection if there's a risk of condensation buildup in the housing (and it's cast iron). Maybe a little on the OD of the bearing to allow slip fit into the bell.

Otherwise I'm not seeing any benefit to extra grease.