There's much debate on this, with some claiming success from a rebuild and others a spate of failures from a rebuild. The problem is the middle bearing which is an odd size for the speed rating.

See here for info on the correct bearings:

http://www.nsr250.net/forums/viewtopic.php?t=201&sid=d0c0880b0cbb71b13ee8e3a89974d578
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