A method and apparatus for determining the average clearance between closely fitting cylindrical parts by determining electrical capacity between the bore and cylinder across a dielectric of known characteristics. The method and apparatus is useful to obtain an accurate measurement of diametral clearance between a piston and bore of a fuel injection pump. In the present invention, an electronic circuit is used to rapidly measure the capacitance magnitude during intermittent and unpredictable periods of nonshort between the piston and bore as the piston is moved inside the bore. The areas of the piston and bore are known and therefore the average clearance therebetween can be calculated.
Harvey S. Benson;