Abstract: The cylinder head of an internal combustion engine has a bore provided with an annular shoulder. A liner "U" shaped in cross section has an outward extending radial end flange which overlies the shoulder. A valve guide is insertable into the bore and has a second shoulder overlying the end flange. The end flange is clamped between seal rings by means of a nut acting through a Belleville spring encircling the valve guide. The liner defines an auxiliary combustion chamber therein and the liner has an opening in a wall thereof which forms a flame passage leading to a main combustion chamber.