The Shimano press fit BB spacer comes inserted into one of the bearings and is marked left/right yet I didn't see left/right on the bearings. Does it matter which way it's installed? If so, is this a rotational or wear concern? FWIW, I installed it left/right properly in case. Thanks.

Most all bearings are not directional (campy Bb cups excepted for their spindle hole rifling) WRT rotational direction. Some cartridges do have seal or fit reasons to be installed a certain way. The Shimano press fit ones that we have dealt with are all bidirectional/mirror images and not side dependent. Andy.

Hi Andy, Thanks. This is an XTR mtb BB. The old one I removed was also marked left/right but it was installed reversed. Not only that, it was a narrower road BB and so the spacer didn't even connect to the other side. In fact, it was floating loose as ride vibration has shook it from the one side it was inserted with. Doh.