Assist gas fuel injection mechanism for 2-cycle internal combustion engine

In an assist gas fuel injection mechanism for 2-cycle internal combustion engine comprising a chamber (21) communicated to a combustion chamber (19) through a communicating passage (30), a rotary valve (40) provided in the communicating passage (30) for controlling the opening and closing of the communicating passage (30), and a fuel injection device (34) provided in the communicating passage (30) between the rotary valve (40) and the chamber (21), such that a highly compressed gas from the chamber (21) and a fuel from the fuel injection device (34) are mixed with each other and a concentrated mixture gas is supplied to the combustion chamber (19) through the communicating passage (30), to minimize the clearance between a valve body (42) and a housing of the rotary valve (40), to reduce leakage of an assist gas for injection, and contrive a reduction in the size of the assist gas fuel injection mechanism. An assist gas fuel injection mechanism for 2-cycle internal combustion engine characterized in that a protective layer is provided on the outside surface of the valve body (42) of the rotary valve (40) by using a material which is softer than the valve body (42) of the rotary valve (40) and the housing of the rotary valve (40) and which is susceptible to plastic deformation.