I'll try to clear this up a bit.
Yep, the newer, inverted Bearing use-require grease.
The older, non-inverted, well type bearings used Oil.
When Mike at VPI suggested-recommended an Oil such as Mobil 1, either 5-50W, or 10-30W, he wasn't haphazardly guessing. These synthetic Oils have very good properties making them ideal for use for their Platter Bearings.
If Thom Mackris of Galibier Design were to chime in, or if you went to Galibier's site, you'll get some basic explanations about bearings, basic properties, and that tolerances can often dictate what viscosity of Oil will be needed.
As Thom would probably tell you, with very tight, precise tolerances, one would never be able to successfully use a relatively heavy viscosity Oil, the Bearing would take forever, and a day to fully seat.
That tolerances will dictate what viscosity will ideally work per given bearing. In the case of a VPI conventional non-inverted bearing, when brand new, a lighter Oil may suffice. if the Bearing"s thrust-bushing surfaces have worn, one then might find the need of a slightly heavier viscosity, to lessen rocking-play of the bearing shaft in the well.
There must be a science to this, in that too light, or too heavy just isn't going to cut it. In every instance-application, one will no doubt need to find the Oil that works "just right".
For me, with my VPI MK-IV Bearing, either Mobil 1 10-30W, or 5-30W works just fine. An oil such as 50W, or heavier in my particular Bearing, would never work, unless I sit on the Platter to get it to seat, and you certainly don't want to do that! Mark
