Method of repairing or modifying the firing deck of an internal combustion engine

A method of repairing or modifying an internal combustion engine having a coolant jacketed engine body including at least one combustion chamber having a firing deck surface with a critical area surrounding an ignition device and subject to thermal stresses, the ignition device being sealed from the coolant jacket by a generally tubular shaped wall structure, comprising providing said firing deck area with a recess encompassing the area subject to the greatest strain during operation, said recess being disposed axially of the ignition device, and drilling an axially disposed internally threaded bore extending into the tubular wall structure from the bottom surface of said recess, providing an insert comprising a circular body to be nested in and to conform to the recess with peripheral clearance and to cover at least a portion of the critical area of the firing deck surface, the diameter of said insert being sightly smaller than that of the recess with the peripheral edge of said insert spaced from the peripheral wall of the recess and providing the peripheral clearance as an expansion area for said insert to accommodate absorption by said insert of heat and strain independently of the engine body, and a centrally disposed externally threaded boss of reduced diameter extending axially from the inner surface of said insert body and threadable into the internally threaded bore in said engine body for securing the insert and body together, inserting said insert boss into said internally threaded bore and rotating said insert to thread said boss into said bore until the inner surface of said insert body firmly engages the floor of said recess, the thickness of said insert being substantially equal to the depth of said recess with the exposed surface of said insert generally contiguous with and conforming to said engine body surface surrounding said recess, said boss having an axially disposed opening therethrough and including a portion defining a set for said ignition device and an opening for exposing said ignition device to said combustion chamber, whereby said insert body is centrally fixed by said boss relative to the point of combustion in said chamber but is free to expand radially from said boss as it absorbs heat of combustion without stress or strain,

• drilling a bore through the enging body from the exterior thereof to the circumferential recess wall and into the periphery of said insert radially of said recess and insert, and inserting a dowell pin into said bores to secure said insert against rotational movement,
• said engine body having inlet and exhaust passageways therethrough and opening into the area encompassed by said recess, determining and marking the location of the centers of said inlet and exhaust openings on said insert, and drilling holes through said insert in alignment with said holes,
• machining the exposed firing deck surface of said insert and the surrounding contiguous area of said engine body to be substantially co-planar,
• said engine body having compressed air inlet opening into said combustion chamber within the area of said recess, drilling a bore through said insert in axial alignment with said compressed air inlet, counterboring said air pressure bore through said insert to provide a flange portion adjacent the base wall of said recess, and inserting a bushing having an outer radial flange overlying said insert flange through said latter bore and into said air inlet with peripheral clearance between both said air pressure bore and counterbored portion and said bushing.