A rotary scraper comprises scraper rods, an annular support member formed with radial openings through which the scraper rods extend respectively, a position-maintaining member, and releasable clamping means for urging the position-maintaining member into contact with the support member. The position-maintaining member has non-slip surface portions against which the rods engage for securing the rods against radial movement with respect to the support member when the position-maintaining member is urged into contact with the support member. The rods are displaceable radially outwards with respect to the support member on release of the clamping means.