If the soil is damp and scrapers are needed, a disc without scrapers is worthless until the soil dries out and can be used succesfully. If the soil is dry and won't pack in between the discs, scrapers aren't necessary. Properly installed scrapers don't require adjustment or maintenence unless the disc is run in roots, sticks or other foreign objects. Generally speaking, only very old or very cheap disc harrows do not have scrapers.