Exhaust port liner for multi-cylinder internal combustion engine

A multi-cylinder internal combustion engine system comprising:

• an engine block having at least two cylinders;
• a plurality of pistons slidably disposed in said cylinders, respectively, for reciprocal movement;
• an engine head securely attached to said engine block to close said cylinders and cooperating therewith to form a plurality of main combustion chambers within said cylinders, respectively;
• said engine head having a plurality of auxiliary combustion chambers connected to said plurality of main combustion chambers, respectively, by respective nozzles which are formed within said engine head;
• means for supplying a lean air-fuel mixture to the main comcombustion chamber during the induction stroke of each of said pistons, which is formed within the cylinder having therein said each piston and a rich air-fuel mixture to the auxiliary combustion chamber connected to said main combustion chamber;
• a spark plug havng its electrode exposed to each of said auxiliary combustion chambers to ignite the rich air-fuel mixture therein thereby to cause a torch flame to propagate through the nozzle toward the main combustion chamber to initiate combustion of the lean air-fuel mixture therein;
• said engine head having an exhaust port passage which has two exhaust intake ends openng to said main combustion chambers, respectively, an exhaust discharge end and a wall defining said exhaust port passage;
• a port liner fixedly mounted by casting within said exhaust port passage and having two exhaust intakes adjacent to said exhaust intake ends, respectively, and an exhaust discharge adjacent to said exhaust discharge end;
• exhaust valve means for closing each of said exhaust intake ends, said exhaust valve means having a valve guide sleeve projecting into said exhaust port passage and a valve member cooperating with one of said exhaust intake ends, said valve member having a stem slidable extending through said valve guide sleeve;
• said port liner having two apertures for permitting said valve guide sleeves to extend, respectively;
• said port liner having a multiple walled construction formed by at least two metal tubes which are partially spaced from each other to form a continuous space therebetween, said space surrounding substantially all areas on the outer surfaces of an inner one of said metal tubes, said metal tubes being joined at areas adjacent to said exhaust intakes, at areas adjacent to the edges of said apertures and at an area adjacent to said exhaust discharge thereby to close said space, said port liner being cast into said engine head when assembled, said port liner having an end portion at each of said exhaust intakes thereof which is embedded into said engine head, the end portion of said port liner at each of said exhaust intakes of said port liner terminating in an outwardly extending flange, said engine head having a plurality of spacer portions projecting inwardly into said exhaust port passage, an outermost one of said two metal tubes having areas which are fixed, by casting, to said spacer portions, said two metal tubes being joined with each other at the area adjacent to said exhaust discharge of said port liner, said last-mentioned joined area being spaced radially inwardly from said wall defining said exhaust port passage, in which said outermost metal tube and said wall defining said exhaust port passage cooperate with each other to form another space surrounding substantially all area on the outer surface of said outermost metal tube, in which said another space is continuous, and in which said another space communicates with an exhaust flow passage defined by said inner metal tube through said apertures.