[itsme]

Hi,

Thanks for the replies.

The shaft is ground, and the bearing is not a sliding fit on it. I haven't measured it, but I'd say it feels just about right. Again, the housing fits haven't been measured, but they feel about right.

As for the discolouration, on closer inspection it seems that the brown colour is only on the surface. There is a matching black/grey deposit on the shaft where the bearing sits. This black deposit scrapes off into a fine powder. Could it be an oil/grease film on the parts that has turned into a carbon deposit with the heat? I have also run a different bearing now with the same result, only worse, and the deposit on the surface was a lot more obvious.

I will probably go with shielded bearings on the next attempt because of the friction concern - thanks for that advice. As far as preload is concerned, these are not the main spindle bearings (they are on a sub shaft), and therefore don't have any preload applied.

The bearing bores are going to be measured up on a CMM today to determine if they are concentric/parallel etc.