The 120F cylinder head and cylinder body together constitute the combustion space, and are equipped with inlet and exhaust valve seats and valve guide holes for the installation of inlet and exhaust valves. The 120F cylinder head also has a cooling water channel to cool the high-temperature gas. In addition, for multi-cylinder engines, the 120F cylinder head must be separated from the combustion chamber of the adjacent cylinder to prevent air leakage or cross-fire.