as Dave says, check bearing make. I rebuilt a square 4 engine for a customer, he suplied the bearings he sourced from an Ariel specialist.
cases heated up old outer fell out, dropped the new one in and left to cool. on turning the case over the bearing fell out. RHP, Timken, SKF are my main choice at a push Koyo (oem for Japanese superbikes).
the main thing is C 3 class of fit, tighter tolerances. the ones for the square 4 were chinese and .003thou under size on outside diameter.