GAS ENGINE AND ASSEMBLING METHOD FOR GAS ENGINE

A gas engine includes a cylinder head (30), a prechamber cap (43) that projects into a main combustion chamber (33) by being inserted into an insertion hole (38) formed in the cylinder head (30), that internally has a prechamber (41), and that supplies a flame generated in the prechamber (41) to the main combustion chamber (33), and a prechamber holder (42) that is disposed inside the cylinder head (30) so as to hold the prechamber cap (43). One of the prechamber cap (43) and the prechamber holder (42) has a concave portion (47) which accommodates an end portion (43a) of the other of the prechamber cap (43) and the prechamber holder (42). An outer diameter of the end portion (43a) is set to be smaller than an inner diameter of the concave portion (47), thereby forming a space (S) between the concave portion (47) and the end portion (43a) at least in a radial direction orthogonal to a central axis.