Gas engine with spark plug and bore-cooling holes

A gas engine comprising:

• a spark plug that is configured to ignite fuel gas supplied into a pre-combustion chamber, the fuel gas sent out from a solenoid valve arranged at an upstream side of a fuel inlet connecting piece, and flown through a fuel inlet passage formed inside said fuel inlet connecting piece, being supplied to the pre-combustion chamber via a mounting hardware piece for mounting the spark plug with which said fuel inlet connecting piece forms a joint, said mounting hardware piece being arranged above the pre-combustion chamber;
• said spark plug fitted on a seat surface of said mounting hardware piece igniting the fuel gas in the pre-combustion chamber by spark discharge,
• wherein a pre-combustion chamber forming-piece is fixed to a bottom wall of a cylinder head, the pre-combustion chamber forming-piece being surrounded by a water chamber and forming the pre-combustion chamber inside, the mounting hardware piece for mounting the spark plug being fixed to a top side of the pre-combustion chamber inside the pre-combustion chamber forming piece,
• a plurality of bore-cooling holes is arranged in the mounting hardware piece in a manner such that the bore-cooling holes surround the seat surface on which the spark plug is seated and extend parallel to a center axis of the spark plug, each of the bore-cooling holes being provided with an inlet side lateral bore-cooling hole and an outlet side lateral bore-cooling hole at a bottom and a top of the bore-cooling hole in a direction of the center axis, respectively, such that a height level where the seat surface is positioned is between a height level of the inlet side lateral bore-cooling hole and a height level of the outlet side lateral bore-cooling hole,
• a check valve insert hole is formed parallel to the center axis of the spark plug inside the mounting hardware piece,
• a junction of said fuel connecting piece and said mounting hardware piece is positioned in an axial section between the height level of the inlet side lateral bore-cooling holes and the height level of the outlet side lateral bore-cooling holes;
• a first check valve which is configured to open with the fuel gas flow toward the pre-combustion chamber, is positioned inside the check valve insert hole and in an axial section between the height level of the inlet side lateral bore-cooling hole and the height level of the outlet side lateral bore-cooling hole;
• and
• said plurality of bore-cooling holes is arranged along a hoop direction around the spark plug so that the plurality of bore-cooling holes surrounds the spark plug in a radial direction and the first check valve in a circumferential direction in a same horizontal cross-section so that cool water from the water chamber flows from said inlet side lateral bore-cooling hole to said outlet side lateral bore-cooling hole via a vertical bore-cooling hole in between so as to cool said seat surface and the first check valve.