Compression Testing

Compression testing is a way to determine the condition of piston/cylinder. Low readings can be caused by worn/stuck rings, head gasket leaks, worn cylinder, or holed piston, among others. High readings can be from excessive carbon deposits, modified heads/cylinders, head gasket thickness, among others.

Readings should be obtained with use of a compression gauge without adapters as they may cause low readings. Insert gauge into sparkplug hole and kick over the engine, holding throttle wide open, until maximum gauge pressure is obtained.

 Compression Specifications

Altitude Correction Factor Table
for Compression Testing

Expected compression tests are specified at sea level. Altitude has an effect on readings obtained and a correction factor must be applied to expected readings taken at other than sea level.

For example: Specified compression = 150psi, Altitude = 2000ft, (150 x .943 = 141.5psi expected@2000ft)