Abstract: An improved replaceable combustion chamber insert for two cycle engines produced by determining, positioning and measuring internal and external cylinder head dimensions of water passages, water connection, and bolt hole patterns within which said insert is to be positioned and machining said insert inner diameters, o-ring groove, dome, and outer shape to correspondingly complement said determined location and measurement dimensions and said cylinder head's bore diameter causing said insert to extend between 5 to 8 thousandths of inch below the bottommost surface of said cylinder head so as to create a compressible surface; and accommodating a spark plug aperture within said insert.