This paper analyzes the failure of a transmission gear in a rotary tiller. The failed gear was examined, the reasons for the failure were determined and preventive methods were explained. The failure types were abrasion and plastic deformation. The reasons for the failure were design errors and material faults. Selection of the gear material was wrong (the material was not hard enough) and the tooth profile was not correct. (C) 2004 Elsevier Ltd. All rights reserved.