Abstract: Valve spring assemblies are checked for proper assembly of keys by ultrasonically scanning a plurality of assemblies along a path crossing the stem, keys and cap to acquire profile data; compensating for temperature effects by determining the average time of flight to the stems, which are nominally the same distance from the ultrasonic sensor, and searching for each individual stem in a window centered on the average time of flight; then defining windows for the keys and cap offset from the measured surface of each stem; and searching the data for points within the respective windows to determine proper positioning of each element. The apparatus includes ultrasonic equipment, a scanning manipulator to move the ultrasonic sensor over the part, and a computer interfaced to the ultrasonic equipment and manipulator for control and data analysis.