turn threadingly engage the spark plug 24 it is also within the scope of the invention that the spark plug carrier 28 be clamped into the head 10 frictionally retained in the head 10 welded or adhered in the head 10 or otherwise the spark plug carrier 28 is of a tubular configuration and open to the combustion chamber 14 at one end to communicate fluids into the interior of the spark plug carrier 28 the spark plug 24 has a seat 32 that abuts and substantially seals against a shoulder 30 in the interior of the spark plug carrier 28 the shoulder 30 serves to position the spark plug 24 in relation to the carrier 28 the spark plug carrier 28 has a shoulder 34 that abuts an interior of the open space 26 to position the carrier 28 in relation to the head 10 and thus the wall surface 12 of the combustion chamber 14 the position of the shoulder 30 of the spark plug carrier 28 and the shoulder 34 of the head 10 are chosen to position the ignition source 18 a predetermined distance from the interior of the combustion chamber 14 and create a protected area 36 within the protected area 36 at least the area about the ignition source 18 is substantially quiescent fig2 depicts an alternate illustrative embodiment incorporating a shielded type spark plug 40 in the spark plug carrier 28 and head 10 arrangement discussed above the shielded type spark plug 40 includes a shield housing 42 surrounding the ignition source 18 the shield housing 42 defines a shielded area 44 coinciding with at least a.