Abstract: A blow-by gas treatment device causes blow-by gas in a space defined by a cylinder head and a head cover in an internal combustion engine to flow back into an intake pipe. The blow-by gas treatment device includes a pipe joint and a blow-by gas pipe connected to the intake pipe. The pipe joint includes a basal end connected to the head cover, a distal end, a sensor-connected part connected to the pressure sensor, and a constriction located closer to the basal end than the sensor-connected part. The blow-by gas pipe is connected to a position of the pipe joint closer to the distal end than the sensor-connected part.

Abstract: A blow-by gas treatment device causes blow-by gas in a space defined by a cylinder head and a head cover in an internal combustion engine to flow back into an intake pipe. The blow-by gas treatment device includes a pipe joint and a blow-by gas pipe connected to the intake pipe. The pipe joint includes a basal end connected to the head cover, a distal end, a sensor-connected part connected to the pressure sensor, and a constriction located closer to the basal end than the sensor-connected part. The blow-by gas pipe is connected to a position of the pipe joint closer to the distal end than the sensor-connected part.

Abstract: A leak check device is for a seal structure of a junction between a first component and a second component. The seal structure is configured such that a fluid passage is defined inside the first and second components connected together, a seal member is attached to the first component, and the seal member prevents leakage of a fluid through the junction. The leak check device includes a test plug configured such that (a) the test plug includes an attachment portion to which the seal member is attached, (b) the attachment portion is connected to the second component separated from the first component, (c) a closed space is defined by an inner peripheral surface of the second component, an outer peripheral surface of the seal member, and an outer peripheral surface of the attachment portion, and (d) the test plug includes an introduction portion through which a test fluid is introduced into the closed space.