The centre bearing has a seal as an integral part of the bearing which would create a bit of friction.
The seal is fixed to the bearing outer ring.

See this post for a picture:
http://nsr250.net/forums/viewtopic.php?p=72125#72125

or just click here and wait for the picture to download.
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...