The study summarizes an experimental investigation on the running-in o
f water-lubricated journal bearings and shaft sleeves made of 10 diffe
rent commercial silicon carbide materials. In each test the sliding su
rfaces became polished and the sliding conditions were transformed fro
m boundary or mixed lubrication to full film lubrication within a rath
er short sliding distance. The initial surface roughness strongly infl
uenced on the initial dynamic coefficient of friction, and on the runn
ing-in distance required to reduce the coefficient of friction from a
level typical of boundary or mixed lubrication to a level typical of f
ull film lubrication. The initial surface roughness of the shaft sleev
e was more slowly removed than that of the bearing, and therefore the
surface quality of the shaft rather than that of the bearing governed
the running-in distance required for the polishing. The initial surfac
e roughness of the bearing practically only influenced the dynamic coe
fficient of friction at the beginning of the running-in procedure. In
comparison with the influence of the surface roughness variations, the
material properties of the silicon carbides studied had a limited inf
luence on the running-in behaviour, which was principally related to a
tribochemical surface polishing process.