Abstract: A leakage tester for identifying defective piston assemblies in a diesel engine includes an adapter fitting for connection to a compression relief valve port on a selected diesel engine cylinder, a fixed length of air conduit having a preselected inside diameter connected at one end to the adapter fitting, and an orifice meter having an air inlet and an air outlet. The orifice meter includes first and second pressure gauges for measuring air inlet pressure and air outlet pressure, respectively, the air conduit having another end connected to the air outlet. In use, the tester is connected to the compression relief valve port and the air inlet of the orifice meter is connected to a source of pressurized air. With the engine advanced to position the piston in the selected cylinder at top dead center, a preselected pressure is applied to the orifice meter. Cylinder leakage is then determined directly from the pressure reading on the second pressure gauge.