Honda CRF 50 pit bike how to port and polish head

new 125cc engine motor 4 stroke motorcycle dirt pit bike for honda crf50 xr50 ca. Rated Power 5.6 kW/7500r/min±375r/min. Lubrication SAE15W/40-SE, 4-stroke gasoline engine oil. Max Torque 8.0 Nm/5000r/min±250r/min.