Ford Motor Company
Device and thread gauging method for ensuring spark plug orientation

Abstract:

A method of operating a measurement device to check an internal thread of a spark plug bore for proper orientation of a spark plug includes positioning a cylinder head relative to the measurement device and measuring a seat surface z-position. The seat surface is configured to seat the spark plug within the spark plug bore. The method includes measuring at least one set of coordinates. Each set of coordinates is at a major diameter of a corresponding threadform of the internal thread. The method includes determining a pitch of the internal thread. The method includes calculating a thread start location where the major diameter of the internal thread intersects the seat surface based on the coordinates of the at least one set of coordinates, the pitch of the internal thread, and the z position of the seat surface. The method includes comparing the thread start location to a reference location.