Rotary jar

In a rotary jar for connecting in a pipe string to produce a sharp upward or downward force on the pipe string when the pipe string becomes stuck in a well bore said jar comprising, an inner tubular mandrel member and an outer tubular anvil member for connecting in a pipe string for limited longitudinal movement relative to each other, impact shoulders on the members limit the relative longitudinal movement of the members, a plurality of laterally spaced rollers attached to the outer surface of the mandrel, longitudinally extending grooves on the inner surface of the anvil, each groove intersecting a U-shaped laterally extending notch formed with curved outwardly flaring walls on the inner surface of the mandrel, and resilient means urging the tubular members to rotate relative to each other in the direction to move the rollers into the U-shaped notches and to allow the roller means to move out of the U-shaped notches when a longitudinal force is imposed on the jar sufficient for the flared walls of the U-shaped notches to provide a lateral component of force on the rollers that will overcome the force of the resilient means and move the rollers out of the U-shaped notches into the longitudinally extending grooves allowing the mandrel to move longitudinally relative to the anvil until the impact shoulders engage and produce a sharp increase in the force exerted by the string when the string is stuck in the hole, the improvement comprising longitudinally extending serpentine grooves that convert a portion of the relative longitudinal motion of the mandrel and the anvil into angular motion tending to rotate the anvil back and forth relative to the mandrel.