Verbrennungsmotor mit einer permanenten Massenelektrode und austauschbarem Mittelelektrodenelement

An internal combustion engine (12) includes a cylinder head (10) and a permanent ground electrode (30) and a replaceable centre electrode element (60) received in a cylinder head bore (20). The permanent ground electrode (30) is affixed to the cylinder head (10) at an inner wall (16) thereof and protrudes into the combustion chamber (18). The ground electrode (30) preferably has a cup-like configuration defining an electrode-receiving hollow (44) in the combustion chamber (18) in registry with the bore (20). The centre electrode element (60) comprises a centre electrode (61) and an insulator body (62) having a shoulder (76) for engaging a seat (32) in the bore (20). The insulator body shoulder (76) is clamped against the seat (32) by an annular retainer nut (82). When the centre electrode element (60) is so clamped, the centre electrode (61) is received in the electrode-receiving hollow (44) defined by the ground electrode (30) in the combustion chamber (18) so as to co-operate with the ground electrode (30) in defining a spark gap (G) therebetween.