A cylinder head for an internal combustion engine in which any of a plurality of valve guides for guiding intake and exhaust poppet valves provided with valve lifters can be press-fitted in fitting holes of the cylinder head with a substantially uniform press fit force. The magnetic layer includes a plurality of regions, a first region having a first magnetic anisotropic energy and a second region having a second magnetic anisotropic energy. The screw rod has a lower end mating a biased member to accurately adjust the interval of a first electric contact of a movable strip and a second electric contact of an electrode thereby to control electric connection or break. A microcontroller receives feedback signals which adjusts polarisation controllers so that the polarisation states of the counter-propagating signals can be controlled to match the amplitude andor phase of the output signals. The method comprises channeling a portion of airflow entering an inlet to the propelling gas turbine engine through a fan assembly and a bypass duct such that the air bypasses the core engine, and channeling a portion of airflow from the bypass duct towards the auxiliary power engine.