use the copper glow plug washer inserted into the exhaust port to lock the piston while removing the nut.this is suggested technigue by clearance lee.i have used the hydraulic lock method when tightening rotors on ducted fan engines where there is no aceess to the exhust port due to the pipe being installed..just make sure all the fuel is drained out before trying to start with an electric starter,turn it over by hand a few times to make sure