Mechanical Lash Adjuster

A mechanical lash adjuster comprising:

• a plunger on which a pressing force of a cam in a valve mechanism acts as an axial load;
• a plunger engaging member put into thread engagement with the plunger in an axial direction to form a thread engagement portion, the plunger engaging member retained so as not to rotate in a circumferential direction of the thread engagement portion;
• and
• a plunger spring urging the plunger in an opposite direction to a direction in which a urging force of a valve spring acts;
• the mechanical lash adjuster interposed between a stem end of a valve urged in a valve closing direction by the valve spring and the cam to adjust a valve clearance,
• wherein a lead angle and flank angles of thread ridges of threads forming the thread engagement portion are set such that
• when an axial load acts on the plunger in either of a plunger extension and a plunger contraction direction, the plunger is prevented from sliding and rotating due to friction torque generated in the thread engagement portion so that the threads are made self-sustaining, and
• when a lateral load acts on the plunger, the plunger is allowed to slide and rotate at the thread engagement portion to move in an axial-load acting direction.