Failure Mode Analysis and Rebuild of a Ford Model T Engine

Abstract

The purpose of this thesis was to characterize the failure mode of the crankshaft from a 1921 Ford Model T. In order to do this, we needed to develop an understanding of the crankshaft’s material properties, derive a model for the forces transmitted through the shaft, and complete a thorough examination of the fracture surface. What we discovered is that the Model T crankshaft failed after an extensive crack developed due to fatiguing of the metal under cyclic loads which were well under the material’s threshold for plastic deformation. The crankshaft was not undersized, but instead doomed from get-go due to selection of a hardened steel with poor fracture toughness which allowed a fatal crack to develop. Recommendations for preventing the type of failure that manifested itself in the crankshaft include either improving the manufacturing processes in order to eliminate surface defects that could nucleate under engine loads or selecting a crankshaft material that was more resistant to the surface defects known to be present in the crankshaft.